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gimple: Canonical order for invariants [PR118902]

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So unlike constants, address invariants are currently put first if
used with a SSA NAME.
It would be better if address invariants are consistent with constants
and this patch changes that.
gcc.dg/tree-ssa/pr118902-1.c is an example where this canonicalization
can help. In it if `p` variable was a global variable, FRE (VN) would have figured
it out that `a` could never be equal to `&p` inside the loop. But without the
canonicalization we end up with `&p == a.0_1` which VN does try to handle for conditional
VN.

Bootstrapped and tested on x86_64.

	PR tree-optimization/118902
gcc/ChangeLog:

	* fold-const.cc (tree_swap_operands_p): Place invariants in the first operand
	if not used with constants.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr118902-1.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
This commit is contained in:
Andrew Pinski 2025-02-13 20:23:48 -08:00
parent 7b4849ec79
commit 16082bdc6b
2 changed files with 27 additions and 0 deletions
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6
gcc/fold-const.cc
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@ -7246,6 +7246,12 @@ tree_swap_operands_p (const_tree arg0, const_tree arg1)
if (TREE_CONSTANT (arg0))
return true;
/* Put invariant address in arg1. */
if (is_gimple_invariant_address (arg1))
return false;
if (is_gimple_invariant_address (arg0))
return true;
/* It is preferable to swap two SSA_NAME to ensure a canonical form
for commutative and comparison operators. Ensuring a canonical
form allows the optimizers to find additional redundancies without

21
gcc/testsuite/gcc.dg/tree-ssa/pr118902-1.c Normal file
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@ -0,0 +1,21 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-optimized" } */
void foo(int);
void l(int**);
int f1(int j, int t)
{
int p = 0;
int *a = &p;
l(&a);
if (a == &p)
return 0;
for(int i = 0; i < j; i++)
{
if (a == &p) foo(p);
}
return 0;
}
/* We should be able to remove the call to foo because a is never equal to &p inside the loop. */
/* { dg-final { scan-tree-dump-not "foo " "optimized"} } */