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tree-optimization/102920 - fix PHI VN with undefined args 

This fixes a latent issue exposed by now allowing VN_TOP in PHI
arguments.  We may only use optimistic equality when merging values on
different edges, not when merging values on the same edge - in particular
we may not choose the undef value on any edge when there's a not undef
value as well.

2021-10-25  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/102920
	* tree-ssa-sccvn.h (expressions_equal_p): Add argument
	controlling VN_TOP matching behavior.
	* tree-ssa-sccvn.c (expressions_equal_p): Likewise.
	(vn_phi_eq): Do not optimistically match VN_TOP.

	* gcc.dg/torture/pr102920.c: New testcase.
This commit is contained in:
Richard Biener 2021-10-25 09:33:15 +02:00
parent 7c20a9b738
commit aa15952d64
3 changed files with 40 additions and 8 deletions
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25
gcc/testsuite/gcc.dg/torture/pr102920.c Normal file
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@ -0,0 +1,25 @@
/* { dg-do run } */
/* { dg-additional-options "-funswitch-loops" } */
unsigned short a = 42;
unsigned short b = 1;
long int c = 1;
unsigned char var_120;
unsigned char var_123;
void __attribute__((noipa)) test(unsigned short a, unsigned short b, long c)
{
for (char i = 0; i < (char)c; i += 5)
if (!b)
var_120 = a;
else
var_123 = a;
}
int main()
{
test(a, b, c);
if (var_123 != 42)
__builtin_abort ();
return 0;
}

21
gcc/tree-ssa-sccvn.c
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@ -4441,11 +4441,15 @@ vn_phi_eq (const_vn_phi_t const vp1, const_vn_phi_t const vp2)
if (inverted_p)
std::swap (te2, fe2);
/* ??? Handle VN_TOP specially. */
/* Since we do not know which edge will be executed we have
to be careful when matching VN_TOP. Be conservative and
only match VN_TOP == VN_TOP for now, we could allow
VN_TOP on the not prevailing PHI though. See for example
PR102920. */
if (! expressions_equal_p (vp1->phiargs[te1->dest_idx],
vp2->phiargs[te2->dest_idx])
vp2->phiargs[te2->dest_idx], false)
|| ! expressions_equal_p (vp1->phiargs[fe1->dest_idx],
vp2->phiargs[fe2->dest_idx]))
vp2->phiargs[fe2->dest_idx], false))
return false;
return true;
@ -4470,7 +4474,7 @@ vn_phi_eq (const_vn_phi_t const vp1, const_vn_phi_t const vp2)
tree phi2op = vp2->phiargs[i];
if (phi1op == phi2op)
continue;
if (!expressions_equal_p (phi1op, phi2op))
if (!expressions_equal_p (phi1op, phi2op, false))
return false;
}
@ -5816,17 +5820,20 @@ get_next_constant_value_id (void)
}
/* Compare two expressions E1 and E2 and return true if they are equal. */
/* Compare two expressions E1 and E2 and return true if they are equal.
If match_vn_top_optimistically is true then VN_TOP is equal to anything,
otherwise VN_TOP only matches VN_TOP. */
bool
expressions_equal_p (tree e1, tree e2)
expressions_equal_p (tree e1, tree e2, bool match_vn_top_optimistically)
{
/* The obvious case. */
if (e1 == e2)
return true;
/* If either one is VN_TOP consider them equal. */
if (e1 == VN_TOP || e2 == VN_TOP)
if (match_vn_top_optimistically
&& (e1 == VN_TOP || e2 == VN_TOP))
return true;
/* SSA_NAME compare pointer equal. */

2
gcc/tree-ssa-sccvn.h
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@ -22,7 +22,7 @@
#define TREE_SSA_SCCVN_H
/* In tree-ssa-sccvn.c */
bool expressions_equal_p (tree, tree);
bool expressions_equal_p (tree, tree, bool = true);
/* TOP of the VN lattice. */