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.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
2021-10-25 Richard Biener <rguent...@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.
---
gcc/testsuite/gcc.dg/torture/pr102920.c | 25 +++++++++++++++++++++++++
gcc/tree-ssa-sccvn.c | 21 ++++++++++++++-------
gcc/tree-ssa-sccvn.h | 2 +-
3 files changed, 40 insertions(+), 8 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/torture/pr102920.c
diff --git a/gcc/testsuite/gcc.dg/torture/pr102920.c
b/gcc/testsuite/gcc.dg/torture/pr102920.c
new file mode 100644
index 00000000000..aa27ac5f6ca
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr102920.c
@@ -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;
+}
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 893b1d0ddaa..d5242597684 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -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. */
diff --git a/gcc/tree-ssa-sccvn.h b/gcc/tree-ssa-sccvn.h
index 8a1b649c726..7d53ab5e39f 100644
--- a/gcc/tree-ssa-sccvn.h
+++ b/gcc/tree-ssa-sccvn.h
@@ -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. */
--
2.31.1
