Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.
Richard.
2018-09-04 Richard Biener <rguent...@suse.de>
PR tree-optimization/87211
* tree-ssa-sccvn.c (visit_phi): When value-numbering to a
backedge value we're supposed to treat as VARYING also number
the PHI to VARYING in case it got a different value-number already.
* gcc.dg/torture/pr87211.c: New testcase.
Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c (revision 264078)
+++ gcc/tree-ssa-sccvn.c (working copy)
@@ -4180,7 +4180,8 @@ visit_phi (gimple *phi, bool *inserted,
}
/* If the value we want to use is the backedge and that wasn't visited
- yet drop to VARYING. This only happens when not iterating.
+ yet or if we should take it as VARYING but it has a non-VARYING
+ value drop to VARYING. This only happens when not iterating.
If we value-number a virtual operand never value-number to the
value from the backedge as that confuses the alias-walking code.
See gcc.dg/torture/pr87176.c. If the value is the same on a
@@ -4190,7 +4191,8 @@ visit_phi (gimple *phi, bool *inserted,
&& TREE_CODE (backedge_val) == SSA_NAME
&& sameval == backedge_val
&& (SSA_NAME_IS_VIRTUAL_OPERAND (backedge_val)
- || !SSA_VISITED (backedge_val)))
+ || !SSA_VISITED (backedge_val)
+ || SSA_VAL (backedge_val) != backedge_val))
/* Note this just drops to VARYING without inserting the PHI into
the hashes. */
result = PHI_RESULT (phi);
Index: gcc/testsuite/gcc.dg/torture/pr87211.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr87211.c (revision 0)
+++ gcc/testsuite/gcc.dg/torture/pr87211.c (working copy)
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+
+int a, b;
+int i(int *);
+int *c(int *d, int *e)
+{
+ for (; b;)
+ d = e;
+ return d;
+}
+void f()
+{
+ for (;;)
+ {
+ int *g[1];
+ int h = 0;
+ for (; h < 3; h++)
+ g[0] = &a;
+ &a == g[0] || i(c((int *)g, g[0]));
+ }
+}
