Add c[lt]z idiom recognition
This recognises the patterns of the form:
while (n & 1) { n >>= 1 }
Unfortunately there are currently two issues relating to this patch.
Firstly, simplify_using_initial_conditions does not recognise that
(n != 0) and ((n & 1) == 0) implies that ((n >> 1) != 0).
This preconditions arise following the loop copy-header pass, and the
assumptions returned by number_of_iterations_exit_assumptions then
prevent final value replacement from using the niter result.
I'm not sure what is the best way to fix this - one approach could be to
modify simplify_using_initial_conditions to handle this sort of case,
but it seems that it basically wants the information that ranger could
give anway, so would something like that be a better option?
The second issue arises in the vectoriser, which is able to determine
that the niter->assumptions are always true.
When building with -march=armv8.4-a+sve -S -O3, we get this codegen:
foo (unsigned int b) {
int c = 0;
if (b == 0)
return PREC;
while (!(b & (1 << (PREC - 1)))) {
b <<= 1;
c++;
}
return c;
}
foo:
.LFB0:
.cfi_startproc
cmp w0, 0
cbz w0, .L6
blt .L7
lsl w1, w0, 1
clz w2, w1
cmp w2, 14
bls .L8
mov x0, 0
cntw x3
add w1, w2, 1
index z1.s, #0, #1
whilelo p0.s, wzr, w1
.L4:
add x0, x0, x3
mov p1.b, p0.b
mov z0.d, z1.d
whilelo p0.s, w0, w1
incw z1.s
b.any .L4
add z0.s, z0.s, #1
lastb w0, p1, z0.s
ret
.p2align 2,,3
.L8:
mov w0, 0
b .L3
.p2align 2,,3
.L13:
lsl w1, w1, 1
.L3:
add w0, w0, 1
tbz w1, #31, .L13
ret
.p2align 2,,3
.L6:
mov w0, 32
ret
.p2align 2,,3
.L7:
mov w0, 0
ret
.cfi_endproc
In essence, the vectoriser uses the niter information to determine
exactly how many iterations of the loop it needs to run. It then uses
SVE whilelo instructions to run this number of iterations. The original
loop counter is also vectorised, despite only being used in the final
iteration, and then the final value of this counter is used as the
return value (which is the same as the number of iterations it computed
in the first place).
This vectorisation is obviously bad, and I think it exposes a latent
bug in the vectoriser, rather than being an issue caused by this
specific patch.
gcc/ChangeLog:
* tree-ssa-loop-niter.cc (number_of_iterations_cltz): New.
(number_of_iterations_bitcount): Add call to the above.
(number_of_iterations_exit_assumptions): Add EQ_EXPR case for
c[lt]z idiom recognition.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/cltz-max.c: New test.
* gcc.dg/tree-ssa/clz-char.c: New test.
* gcc.dg/tree-ssa/clz-int.c: New test.
* gcc.dg/tree-ssa/clz-long-long.c: New test.
* gcc.dg/tree-ssa/clz-long.c: New test.
* gcc.dg/tree-ssa/ctz-char.c: New test.
* gcc.dg/tree-ssa/ctz-int.c: New test.
* gcc.dg/tree-ssa/ctz-long-long.c: New test.
* gcc.dg/tree-ssa/ctz-long.c: New test.
This commit is contained in:
Andrew Carlotti
parent
0419b9b800
commit
4798080d4a
10 changed files with 517 additions and 0 deletions
72
gcc/testsuite/gcc.dg/tree-ssa/cltz-max.c
Normal file
72
gcc/testsuite/gcc.dg/tree-ssa/cltz-max.c
Normal file
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@ -0,0 +1,72 @@
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/* { dg-do compile } */
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/* { dg-options "-O2 -fno-tree-loop-optimize -fdump-tree-optimized" } */
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#define PREC (__CHAR_BIT__)
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int clz_count1 (unsigned char b) {
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int c = 0;
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if (b == 0)
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return 0;
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while (!(b & (1 << (PREC - 1)))) {
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b <<= 1;
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c++;
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}
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if (c <= PREC - 1)
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return 0;
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else
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return 34567;
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}
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int clz_count2 (unsigned char b) {
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int c = 0;
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if (b == 0)
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return 0;
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while (!(b & (1 << PREC - 1))) {
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b <<= 1;
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c++;
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}
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if (c <= PREC - 2)
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return 0;
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else
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return 76543;
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}
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int ctz_count1 (unsigned char b) {
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int c = 0;
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if (b == 0)
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return 0;
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while (!(b & 1)) {
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b >>= 1;
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c++;
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}
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if (c <= PREC - 1)
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return 0;
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else
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return 23456;
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}
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int ctz_count2 (unsigned char b) {
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int c = 0;
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if (b == 0)
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return 0;
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while (!(b & 1)) {
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b >>= 1;
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c++;
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}
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if (c <= PREC - 2)
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return 0;
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else
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return 65432;
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}
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/* { dg-final { scan-tree-dump-times "34567" 0 "optimized" } } */
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/* { dg-final { scan-tree-dump-times "76543" 1 "optimized" } } */
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/* { dg-final { scan-tree-dump-times "23456" 0 "optimized" } } */
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/* { dg-final { scan-tree-dump-times "65432" 1 "optimized" } } */
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34
gcc/testsuite/gcc.dg/tree-ssa/clz-char.c
Normal file
34
gcc/testsuite/gcc.dg/tree-ssa/clz-char.c
Normal file
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@ -0,0 +1,34 @@
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/* { dg-do run } */
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/* { dg-require-effective-target clzl } */
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/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
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#define PREC (__CHAR_BIT__)
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int
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__attribute__ ((noinline, noclone))
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foo (unsigned char b) {
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int c = 0;
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if (b == 0)
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return PREC;
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while (!(b & (1 << (PREC - 1)))) {
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b <<= 1;
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c++;
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}
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return c;
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}
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int main()
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{
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if (foo(0) != PREC)
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__builtin_abort ();
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if (foo(1 << (PREC - 1)) != 0)
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__builtin_abort ();
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if (foo(35) != PREC - 6)
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__builtin_abort ();
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return 0;
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}
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/* { dg-final { scan-tree-dump-times "__builtin_clz|\\.CLZ" 1 "optimized" } } */
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34
gcc/testsuite/gcc.dg/tree-ssa/clz-int.c
Normal file
34
gcc/testsuite/gcc.dg/tree-ssa/clz-int.c
Normal file
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@ -0,0 +1,34 @@
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/* { dg-do run } */
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/* { dg-require-effective-target clzl } */
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/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
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#define PREC (__CHAR_BIT__ * __SIZEOF_INT__)
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int
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__attribute__ ((noinline, noclone))
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foo (unsigned int b) {
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int c = 0;
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if (b == 0)
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return PREC;
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while (!(b & (1 << (PREC - 1)))) {
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b <<= 1;
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c++;
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}
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return c;
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}
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int main()
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{
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if (foo(0) != PREC)
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__builtin_abort ();
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if (foo(1 << (PREC - 1)) != 0)
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__builtin_abort ();
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if (foo(35) != PREC - 6)
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__builtin_abort ();
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return 0;
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}
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/* { dg-final { scan-tree-dump-times "__builtin_clz|\\.CLZ" 1 "optimized" } } */
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34
gcc/testsuite/gcc.dg/tree-ssa/clz-long-long.c
Normal file
34
gcc/testsuite/gcc.dg/tree-ssa/clz-long-long.c
Normal file
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@ -0,0 +1,34 @@
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/* { dg-do run } */
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/* { dg-require-effective-target clzll } */
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/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
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#define PREC (__CHAR_BIT__ * __SIZEOF_LONG_LONG__)
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int
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__attribute__ ((noinline, noclone))
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foo (unsigned long long b) {
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int c = 0;
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if (b == 0)
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return PREC;
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while (!(b & (1LL << (PREC - 1)))) {
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b <<= 1;
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c++;
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}
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return c;
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}
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int main()
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{
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if (foo(0) != PREC)
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__builtin_abort ();
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if (foo(1LL << (PREC - 1)) != 0)
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__builtin_abort ();
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if (foo(35) != PREC - 6)
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__builtin_abort ();
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return 0;
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}
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/* { dg-final { scan-tree-dump-times "__builtin_clz|\\.CLZ" 1 "optimized" } } */
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34
gcc/testsuite/gcc.dg/tree-ssa/clz-long.c
Normal file
34
gcc/testsuite/gcc.dg/tree-ssa/clz-long.c
Normal file
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@ -0,0 +1,34 @@
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/* { dg-do run } */
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/* { dg-require-effective-target clzl } */
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/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
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#define PREC (__CHAR_BIT__ * __SIZEOF_LONG__)
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int
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__attribute__ ((noinline, noclone))
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foo (unsigned long b) {
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int c = 0;
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if (b == 0)
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return PREC;
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while (!(b & (1L << (PREC - 1)))) {
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b <<= 1;
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c++;
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}
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return c;
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}
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int main()
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{
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if (foo(0) != PREC)
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__builtin_abort ();
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if (foo(1L << (PREC - 1)) != 0)
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__builtin_abort ();
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if (foo(35) != PREC - 6)
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__builtin_abort ();
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return 0;
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}
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/* { dg-final { scan-tree-dump-times "__builtin_clz|\\.CLZ" 1 "optimized" } } */
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36
gcc/testsuite/gcc.dg/tree-ssa/ctz-char.c
Normal file
36
gcc/testsuite/gcc.dg/tree-ssa/ctz-char.c
Normal file
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@ -0,0 +1,36 @@
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/* { dg-do run } */
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/* { dg-require-effective-target ctz } */
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/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
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#define PREC (__CHAR_BIT__)
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int
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__attribute__ ((noinline, noclone))
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foo (unsigned char b) {
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int c = 0;
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if (b == 0)
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return PREC;
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while (!(b & 1)) {
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b >>= 1;
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c++;
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}
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return c;
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}
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int main()
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{
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if (foo(0) != PREC)
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__builtin_abort ();
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if (foo(128) != 7)
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__builtin_abort ();
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if (foo(96) != 5)
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__builtin_abort ();
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if (foo(35) != 0)
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__builtin_abort ();
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return 0;
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}
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/* { dg-final { scan-tree-dump-times "__builtin_ctz|\\.CTZ" 1 "optimized" } } */
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36
gcc/testsuite/gcc.dg/tree-ssa/ctz-int.c
Normal file
36
gcc/testsuite/gcc.dg/tree-ssa/ctz-int.c
Normal file
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@ -0,0 +1,36 @@
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/* { dg-do run } */
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/* { dg-require-effective-target ctz } */
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/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
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#define PREC (__CHAR_BIT__ * __SIZEOF_INT__)
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int
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__attribute__ ((noinline, noclone))
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foo (unsigned int b) {
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int c = 0;
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if (b == 0)
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return PREC;
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while (!(b & 1)) {
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b >>= 1;
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c++;
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}
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return c;
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}
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int main()
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{
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if (foo(0) != PREC)
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__builtin_abort ();
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if (foo(1 << (PREC - 1)) != PREC - 1)
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__builtin_abort ();
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if (foo(96) != 5)
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__builtin_abort ();
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if (foo(35) != 0)
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__builtin_abort ();
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return 0;
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}
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/* { dg-final { scan-tree-dump-times "__builtin_ctz|\\.CTZ" 1 "optimized" } } */
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36
gcc/testsuite/gcc.dg/tree-ssa/ctz-long-long.c
Normal file
36
gcc/testsuite/gcc.dg/tree-ssa/ctz-long-long.c
Normal file
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@ -0,0 +1,36 @@
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/* { dg-do run } */
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/* { dg-require-effective-target ctzll } */
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/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
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#define PREC (__CHAR_BIT__ * __SIZEOF_LONG_LONG__)
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int
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__attribute__ ((noinline, noclone))
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foo (unsigned long long b) {
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int c = 0;
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if (b == 0)
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return PREC;
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while (!(b & 1)) {
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b >>= 1;
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c++;
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}
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return c;
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}
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int main()
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{
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if (foo(0) != PREC)
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__builtin_abort ();
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if (foo(1LL << (PREC - 1)) != PREC - 1)
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__builtin_abort ();
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if (foo(96) != 5)
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__builtin_abort ();
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if (foo(35) != 0)
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__builtin_abort ();
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return 0;
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}
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/* { dg-final { scan-tree-dump-times "__builtin_ctz|\\.CTZ" 1 "optimized" } } */
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36
gcc/testsuite/gcc.dg/tree-ssa/ctz-long.c
Normal file
36
gcc/testsuite/gcc.dg/tree-ssa/ctz-long.c
Normal file
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@ -0,0 +1,36 @@
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/* { dg-do run } */
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/* { dg-require-effective-target ctzl } */
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/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
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#define PREC (__CHAR_BIT__ * __SIZEOF_LONG__)
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int
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__attribute__ ((noinline, noclone))
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foo (unsigned long b) {
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int c = 0;
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if (b == 0)
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return PREC;
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while (!(b & 1)) {
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b >>= 1;
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c++;
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}
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return c;
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}
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int main()
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{
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if (foo(0) != PREC)
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__builtin_abort ();
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if (foo(1L << (PREC - 1)) != PREC - 1)
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__builtin_abort ();
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if (foo(96) != 5)
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__builtin_abort ();
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if (foo(35) != 0)
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__builtin_abort ();
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return 0;
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}
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/* { dg-final { scan-tree-dump-times "__builtin_ctz|\\.CTZ" 1 "optimized" } } */
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@ -2304,6 +2304,167 @@ build_cltz_expr (tree src, bool leading, bool define_at_zero)
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return call;
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}
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/* See comment below for number_of_iterations_bitcount.
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For c[lt]z, we have:
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modify:
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iv_2 = iv_1 << 1 OR iv_1 >> 1
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test:
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if (iv & 1 << (prec-1)) OR (iv & 1)
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modification count:
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src precision - c[lt]z (src)
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*/
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static bool
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number_of_iterations_cltz (loop_p loop, edge exit,
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enum tree_code code,
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class tree_niter_desc *niter)
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{
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bool modify_before_test = true;
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HOST_WIDE_INT max;
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int checked_bit;
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tree iv_2;
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/* Check that condition for staying inside the loop is like
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if (iv == 0). */
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gimple *cond_stmt = last_stmt (exit->src);
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if (!cond_stmt
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|| gimple_code (cond_stmt) != GIMPLE_COND
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|| (code != EQ_EXPR && code != GE_EXPR)
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|| !integer_zerop (gimple_cond_rhs (cond_stmt))
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|| TREE_CODE (gimple_cond_lhs (cond_stmt)) != SSA_NAME)
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return false;
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if (code == EQ_EXPR)
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{
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/* Make sure we check a bitwise and with a suitable constant */
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gimple *and_stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (cond_stmt));
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if (!is_gimple_assign (and_stmt)
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|| gimple_assign_rhs_code (and_stmt) != BIT_AND_EXPR
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|| !integer_pow2p (gimple_assign_rhs2 (and_stmt)))
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return false;
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checked_bit = tree_log2 (gimple_assign_rhs2 (and_stmt));
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iv_2 = gimple_assign_rhs1 (and_stmt);
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}
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else
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{
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/* We have a GE_EXPR - a signed comparison with zero is equivalent to
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testing the leading bit, so check for this pattern too. */
|
||||
|
||||
iv_2 = gimple_cond_lhs (cond_stmt);
|
||||
tree test_value_type = TREE_TYPE (iv_2);
|
||||
|
||||
if (TYPE_UNSIGNED (test_value_type))
|
||||
return false;
|
||||
|
||||
gimple *test_value_stmt = SSA_NAME_DEF_STMT (iv_2);
|
||||
|
||||
if (is_gimple_assign (test_value_stmt)
|
||||
&& gimple_assign_rhs_code (test_value_stmt) == NOP_EXPR)
|
||||
{
|
||||
/* If the test value comes from a NOP_EXPR, then we need to unwrap
|
||||
this. We conservatively require that both types have the same
|
||||
precision. */
|
||||
iv_2 = gimple_assign_rhs1 (test_value_stmt);
|
||||
tree rhs_type = TREE_TYPE (iv_2);
|
||||
if (TREE_CODE (rhs_type) != INTEGER_TYPE
|
||||
|| (TYPE_PRECISION (rhs_type)
|
||||
!= TYPE_PRECISION (test_value_type)))
|
||||
return false;
|
||||
}
|
||||
|
||||
checked_bit = TYPE_PRECISION (test_value_type) - 1;
|
||||
}
|
||||
|
||||
gimple *iv_2_stmt = SSA_NAME_DEF_STMT (iv_2);
|
||||
|
||||
/* If the test comes before the iv modification, then these will actually be
|
||||
iv_1 and a phi node. */
|
||||
if (gimple_code (iv_2_stmt) == GIMPLE_PHI
|
||||
&& gimple_bb (iv_2_stmt) == loop->header
|
||||
&& gimple_phi_num_args (iv_2_stmt) == 2
|
||||
&& (TREE_CODE (gimple_phi_arg_def (iv_2_stmt,
|
||||
loop_latch_edge (loop)->dest_idx))
|
||||
== SSA_NAME))
|
||||
{
|
||||
/* iv_2 is actually one of the inputs to the phi. */
|
||||
iv_2 = gimple_phi_arg_def (iv_2_stmt, loop_latch_edge (loop)->dest_idx);
|
||||
iv_2_stmt = SSA_NAME_DEF_STMT (iv_2);
|
||||
modify_before_test = false;
|
||||
}
|
||||
|
||||
/* Make sure iv_2_stmt is a logical shift by one stmt:
|
||||
iv_2 = iv_1 {<<|>>} 1 */
|
||||
if (!is_gimple_assign (iv_2_stmt)
|
||||
|| (gimple_assign_rhs_code (iv_2_stmt) != LSHIFT_EXPR
|
||||
&& (gimple_assign_rhs_code (iv_2_stmt) != RSHIFT_EXPR
|
||||
|| !TYPE_UNSIGNED (TREE_TYPE (gimple_assign_lhs (iv_2_stmt)))))
|
||||
|| !integer_onep (gimple_assign_rhs2 (iv_2_stmt)))
|
||||
return false;
|
||||
|
||||
bool left_shift = (gimple_assign_rhs_code (iv_2_stmt) == LSHIFT_EXPR);
|
||||
|
||||
tree iv_1 = gimple_assign_rhs1 (iv_2_stmt);
|
||||
|
||||
/* Check the recurrence. */
|
||||
gimple *phi = SSA_NAME_DEF_STMT (iv_1);
|
||||
if (gimple_code (phi) != GIMPLE_PHI
|
||||
|| (gimple_bb (phi) != loop_latch_edge (loop)->dest)
|
||||
|| (iv_2 != gimple_phi_arg_def (phi, loop_latch_edge (loop)->dest_idx)))
|
||||
return false;
|
||||
|
||||
/* We found a match. */
|
||||
tree src = gimple_phi_arg_def (phi, loop_preheader_edge (loop)->dest_idx);
|
||||
int src_precision = TYPE_PRECISION (TREE_TYPE (src));
|
||||
|
||||
/* Apply any needed preprocessing to src. */
|
||||
int num_ignored_bits;
|
||||
if (left_shift)
|
||||
num_ignored_bits = src_precision - checked_bit - 1;
|
||||
else
|
||||
num_ignored_bits = checked_bit;
|
||||
|
||||
if (modify_before_test)
|
||||
num_ignored_bits++;
|
||||
|
||||
if (num_ignored_bits != 0)
|
||||
src = fold_build2 (left_shift ? LSHIFT_EXPR : RSHIFT_EXPR,
|
||||
TREE_TYPE (src), src,
|
||||
build_int_cst (integer_type_node, num_ignored_bits));
|
||||
|
||||
/* Get the corresponding c[lt]z builtin. */
|
||||
tree expr = build_cltz_expr (src, left_shift, false);
|
||||
|
||||
if (!expr)
|
||||
return false;
|
||||
|
||||
max = src_precision - num_ignored_bits - 1;
|
||||
|
||||
expr = fold_convert (unsigned_type_node, expr);
|
||||
|
||||
tree assumptions = fold_build2 (NE_EXPR, boolean_type_node, src,
|
||||
build_zero_cst (TREE_TYPE (src)));
|
||||
|
||||
niter->assumptions = simplify_using_initial_conditions (loop, assumptions);
|
||||
niter->may_be_zero = boolean_false_node;
|
||||
niter->niter = simplify_using_initial_conditions (loop, expr);
|
||||
|
||||
if (TREE_CODE (niter->niter) == INTEGER_CST)
|
||||
niter->max = tree_to_uhwi (niter->niter);
|
||||
else
|
||||
niter->max = max;
|
||||
|
||||
niter->bound = NULL_TREE;
|
||||
niter->cmp = ERROR_MARK;
|
||||
|
||||
return true;
|
||||
}
|
||||
|
||||
/* See comment below for number_of_iterations_bitcount.
|
||||
For c[lt]z complement, we have:
|
||||
|
||||
|
|
@ -2464,6 +2625,7 @@ number_of_iterations_bitcount (loop_p loop, edge exit,
|
|||
class tree_niter_desc *niter)
|
||||
{
|
||||
return (number_of_iterations_popcount (loop, exit, code, niter)
|
||||
|| number_of_iterations_cltz (loop, exit, code, niter)
|
||||
|| number_of_iterations_cltz_complement (loop, exit, code, niter));
|
||||
}
|
||||
|
||||
|
|
@ -2992,6 +3154,9 @@ number_of_iterations_exit_assumptions (class loop *loop, edge exit,
|
|||
case NE_EXPR:
|
||||
break;
|
||||
|
||||
case EQ_EXPR:
|
||||
return number_of_iterations_cltz (loop, exit, code, niter);
|
||||
|
||||
default:
|
||||
return false;
|
||||
}
|
||||
|
|
|
|||
Loading…
Add table
Reference in a new issue