Hi!
The following place in value_replacement is after proving that
x == cst1 ? cst2 : x
phi result is only used in a comparison with constant which doesn't
care if it compares cst1 or cst2 and replaces it with x.
The testcase is miscompiled because we have after the replacement
incorrect range info for the phi result, we would need to
effectively union the phi result range with cst1 (oarg in the code)
because previously that constant might be missing in the range, but
newly it can appear (we've just verified that the single use stmt
of the phi result doesn't care about that value in particular).
The following patch just resets the info, bootstrapped/regtested
on x86_64-linux and i686-linux, ok for trunk?
Aldy/Andrew, how would one instead union the SSA_NAME_RANGE_INFO
with some INTEGER_CST and store it back into SSA_NAME_RANGE_INFO
(including adjusting non-zero bits and the like)?
2022-12-22 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/108166
* tree-ssa-phiopt.cc (value_replacement): For the maybe_equal_p
case turned into equal_p reset SSA_NAME_RANGE_INFO of phi result.
* g++.dg/torture/pr108166.C: New test.
--- gcc/tree-ssa-phiopt.cc.jj 2022-10-28 11:00:53.970243821 +0200
+++ gcc/tree-ssa-phiopt.cc 2022-12-21 14:27:58.118326548 +0100
@@ -1491,6 +1491,12 @@ value_replacement (basic_block cond_bb,
default:
break;
}
+ if (equal_p)
+ /* After the optimization PHI result can have value
+ which it couldn't have previously.
+ We could instead of resetting it union the range
+ info with oarg. */
+ reset_flow_sensitive_info (gimple_phi_result (phi));
if (equal_p && MAY_HAVE_DEBUG_BIND_STMTS)
{
imm_use_iterator imm_iter;
--- gcc/testsuite/g++.dg/torture/pr108166.C.jj 2022-12-21 14:31:02.638661322
+0100
+++ gcc/testsuite/g++.dg/torture/pr108166.C 2022-12-21 14:30:45.441909725
+0100
@@ -0,0 +1,26 @@
+// PR tree-optimization/108166
+// { dg-do run }
+
+bool a, b;
+int d, c;
+
+const int &
+foo (const int &f, const int &g)
+{
+ return !f ? f : g;
+}
+
+__attribute__((noipa)) void
+bar (int)
+{
+}
+
+int
+main ()
+{
+ c = foo (b, 0) > ((b ? d : b) ?: 8);
+ a = b ? d : b;
+ bar (a);
+ if (a != 0)
+ __builtin_abort ();
+}
Jakub
