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re PR tree-optimization/21137 (Convert (a >> 2) & 1 != 0 into a & 4 != 0)

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2006-02-26  Roger Sayle  <roger@eyesopen.com>
	    James A. Morrison  <phython@gcc.gnu.org>

	PR middle-end/21137
	* fold-const.c (fold_binary) <EQ_EXPR>:  Fold ((X>>C1)&C2) eq/ne 0,
	when C2 is a power of two, as either (X&(C2<<C1)) eq/ne 0 if the
	new constant C2<<C1, or as (X<0) or (X,false) depending upon the
	signedness of the shift operation.

	* gcc.dg/fold-eqandshift-1.c: New test case.


Co-Authored-By: James A. Morrison <phython@gcc.gnu.org>

From-SVN: r111453
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Roger Sayle 2006-02-26 15:36:52 +00:00 • committed by Roger Sayle
parent cd683f6da5
commit a861485caf
4 changed files with 106 additions and 0 deletions
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9
gcc/ChangeLog
View file

@ -1,3 +1,12 @@
2006-02-26 Roger Sayle <roger@eyesopen.com>
James A. Morrison <phython@gcc.gnu.org>
PR middle-end/21137
* fold-const.c (fold_binary) <EQ_EXPR>: Fold ((X>>C1)&C2) eq/ne 0,
when C2 is a power of two, as either (X&(C2<<C1)) eq/ne 0 if the
new constant C2<<C1, or as (X<0) or (X,false) depending upon the
signedness of the shift operation.
2006-02-26 Dorit Nuzman <dorit@il.ibm.com>
PR tree-optimization/26359

46
gcc/fold-const.c
View file

@ -9653,6 +9653,52 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
fold_convert (newtype, arg1));
}
/* Fold ((X >> C1) & C2) == 0 and ((X >> C1) & C2) != 0 where
C1 is a valid shift constant, and C2 is a power of two, i.e.
a single bit. */
if (TREE_CODE (arg0) == BIT_AND_EXPR
&& TREE_CODE (TREE_OPERAND (arg0, 0)) == RSHIFT_EXPR
&& TREE_CODE (TREE_OPERAND (TREE_OPERAND (arg0, 0), 1))
== INTEGER_CST
&& integer_pow2p (TREE_OPERAND (arg0, 1))
&& integer_zerop (arg1))
{
tree itype = TREE_TYPE (arg0);
unsigned HOST_WIDE_INT prec = TYPE_PRECISION (itype);
tree arg001 = TREE_OPERAND (TREE_OPERAND (arg0, 0), 1);
/* Check for a valid shift count. */
if (TREE_INT_CST_HIGH (arg001) == 0
&& TREE_INT_CST_LOW (arg001) < prec)
{
tree arg01 = TREE_OPERAND (arg0, 1);
tree arg000 = TREE_OPERAND (TREE_OPERAND (arg0, 0), 0);
unsigned HOST_WIDE_INT log2 = tree_log2 (arg01);
/* If (C2 << C1) doesn't overflow, then ((X >> C1) & C2) != 0
can be rewritten as (X & (C2 << C1)) != 0. */
if ((log2 + TREE_INT_CST_LOW (arg01)) < prec)
{
tem = fold_build2 (LSHIFT_EXPR, itype, arg01, arg001);
tem = fold_build2 (BIT_AND_EXPR, itype, arg000, tem);
return fold_build2 (code, type, tem, arg1);
}
/* Otherwise, for signed (arithmetic) shifts,
((X >> C1) & C2) != 0 is rewritten as X < 0, and
((X >> C1) & C2) == 0 is rewritten as X >= 0. */
else if (!TYPE_UNSIGNED (itype))
return fold_build2 (code == EQ_EXPR ? GE_EXPR : LT_EXPR, type,
arg000, build_int_cst (itype, 0));
/* Otherwise, of unsigned (logical) shifts,
((X >> C1) & C2) != 0 is rewritten as (X,false), and
((X >> C1) & C2) == 0 is rewritten as (X,true). */
else
return omit_one_operand (type,
code == EQ_EXPR ? integer_one_node
: integer_zero_node,
arg000);
}
}
/* If this is an NE comparison of zero with an AND of one, remove the
comparison since the AND will give the correct value. */
if (code == NE_EXPR

5
gcc/testsuite/ChangeLog
View file

@ -1,3 +1,8 @@
2006-02-26 Roger Sayle <roger@eyesopen.com>
PR middle-end/21137
* gcc.dg/fold-eqandshift-1.c: New test case.
2006-02-26 Dorit Nuzman <dorit@il.ibm.com>
PR tree-optimization/25125

46
gcc/testsuite/gcc.dg/fold-eqandshift-1.c Normal file
View file

@ -0,0 +1,46 @@
/* PR middle-end/21137 */
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-original" } */
extern void foo();
void test1(int a)
{
if ((a >> 3) & 1)
foo ();
}
void test2(int b)
{
if ((b >> 3) & 4)
foo ();
}
int test3(int c)
{
return (c >> 3) & 1;
}
int test4(int d)
{
return (d >> 3) & 4;
}
#if 0
void test5(int e)
{
if ((e >> 31) & 64)
foo();
}
void test6(unsigned int f)
{
if ((f >> 31) & 64)
foo();
}
#endif
/* { dg-final { scan-tree-dump-times "\\(a \& 8\\) != 0" 1 "original" } } */
/* { dg-final { scan-tree-dump-times "\\(b \& 32\\) != 0" 1 "original" } } */
/* { dg-final { scan-tree-dump-times "c >> 3 \& 1" 1 "original" } } */
/* { dg-final { scan-tree-dump-times "d >> 3 \& 4" 1 "original" } } */
/* { dg-final { cleanup-tree-dump "original" } } */