When the patch for PR114074 was applied we saw a good boost in exchange2.
This boost was partially caused by a simplification of the addressing modes.
With the patch applied IV opts saw the following form for the base addressing;
Base: (integer(kind=4) *) &block + ((sizetype) ((unsigned long) l0_19(D) *
324) + 36)
vs what we normally get:
Base: (integer(kind=4) *) &block + ((sizetype) ((integer(kind=8)) l0_19(D)
* 81) + 9) * 4
This is because the patch promoted multiplies where one operand is a constant
from a signed multiply to an unsigned one, to attempt to fold away the constant.
This patch attempts the same but due to the various problems with SCEV and
niters not being able to analyze the resulting forms (i.e. PR114322) we can't
do it during SCEV or in the general form like in fold-const like extract_muldiv
attempts.
Instead this applies the simplification during IVopts initialization when we
create the IV. This allows IV opts to see the simplified form without
influencing the rest of the compiler.
as mentioned in PR114074 it would be good to fix the missed optimization in the
other passes so we can perform this in general.
The reason this has a big impact on Fortran code is that Fortran doesn't seem to
have unsigned integer types. As such all it's addressing are created with
signed types and folding does not happen on them due to the possible overflow.
concretely on AArch64 this changes the results from generation:
mov x27, -108
mov x24, -72
mov x23, -36
add x21, x1, x0, lsl 2
add x19, x20, x22
.L5:
add x0, x22, x19
add x19, x19, 324
ldr d1, [x0, x27]
add v1.2s, v1.2s, v15.2s
str d1, [x20, 216]
ldr d0, [x0, x24]
add v0.2s, v0.2s, v15.2s
str d0, [x20, 252]
ldr d31, [x0, x23]
add v31.2s, v31.2s, v15.2s
str d31, [x20, 288]
bl digits_20_
cmp x21, x19
bne .L5
into:
.L5:
ldr d1, [x19, -108]
add v1.2s, v1.2s, v15.2s
str d1, [x20, 216]
ldr d0, [x19, -72]
add v0.2s, v0.2s, v15.2s
str d0, [x20, 252]
ldr d31, [x19, -36]
add x19, x19, 324
add v31.2s, v31.2s, v15.2s
str d31, [x20, 288]
bl digits_20_
cmp x21, x19
bne .L5
The two patches together results in a 10% performance increase in exchange2 in
SPECCPU 2017 and a 4% reduction in binary size and a 5% improvement in compile
time. There's also a 5% performance improvement in fotonik3d and similar
reduction in binary size.
The patch folds every IV to unsigned to canonicalize them. At the end of the
pass we match.pd will then remove unneeded conversions.
Note that we cannot force everything to unsigned, IVops requires that array
address expressions remain as such. Folding them results in them becoming
pointer expressions for which some optimizations in IVopts do not run.
gcc/ChangeLog:
PR tree-optimization/114932
* tree-ssa-loop-ivopts.cc (alloc_iv): Perform affine unsigned fold.
gcc/testsuite/ChangeLog:
PR tree-optimization/114932
* gcc.dg/tree-ssa/pr64705.c: Update dump file scan.
* gcc.target/i386/pr115462.c: The testcase shares 3 IVs which calculates
the same thing but with a slightly different increment offset. The test
checks for 3 complex addressing loads, one for each IV. But with this
change they now all share one IV. That is the loop now only has one
complex addressing. This is ultimately driven by the backend costing
and the current costing says this is preferred so updating the testcase.
* gfortran.dg/addressing-modes_1.f90: New test.
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