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tree-optimization/105971 - less surprising refs_may_alias_p_2

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When DSE asks whether __real a is using __imag a it gets a surprising
result when a is a FUNCTION_DECL.  The following makes sure this case
is less surprising to callers but keeping the bail-out for the
non-decl case where it is true that PTA doesn't track aliases to code
correctly.

2022-06-15  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/105971
	* tree-ssa-alias.cc (refs_may_alias_p_2): Put bail-out for
	FUNCTION_DECL and LABEL_DECL refs after decl-decl disambiguation
	to leak less surprising alias results.

	* gcc.dg/torture/pr106971.c: New testcase.
This commit is contained in:
Richard Biener 2022-06-15 11:27:31 +02:00
parent edb9330c29
commit 8c2733e16e
2 changed files with 21 additions and 9 deletions
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12
gcc/testsuite/gcc.dg/torture/pr106971.c Normal file
View file

@ -0,0 +1,12 @@
/* { dg-do compile } */
void a()
{
int b;
int c;
int d = (__INTPTR_TYPE__)a;
_Complex float *e = (_Complex float *)a;
for (;;) {
(*e += d) / b ?: 0;
}
}

18
gcc/tree-ssa-alias.cc
View file

@ -2397,15 +2397,6 @@ refs_may_alias_p_2 (ao_ref *ref1, ao_ref *ref2, bool tbaa_p)
|| CONSTANT_CLASS_P (base2))
return false;
/* We can end up referring to code via function and label decls.
As we likely do not properly track code aliases conservatively
bail out. */
if (TREE_CODE (base1) == FUNCTION_DECL
|| TREE_CODE (base1) == LABEL_DECL
|| TREE_CODE (base2) == FUNCTION_DECL
|| TREE_CODE (base2) == LABEL_DECL)
return true;
/* Two volatile accesses always conflict. */
if (ref1->volatile_p
&& ref2->volatile_p)
@ -2432,6 +2423,15 @@ refs_may_alias_p_2 (ao_ref *ref1, ao_ref *ref2, bool tbaa_p)
ref2ref, base2, offset2, max_size2,
ref2->size);
/* We can end up referring to code via function and label decls.
As we likely do not properly track code aliases conservatively
bail out. */
if (TREE_CODE (base1) == FUNCTION_DECL
|| TREE_CODE (base1) == LABEL_DECL
|| TREE_CODE (base2) == FUNCTION_DECL
|| TREE_CODE (base2) == LABEL_DECL)
return true;
/* Handle restrict based accesses.
??? ao_ref_base strips inner MEM_REF [&decl], recover from that
here. */