Hi!
The following testcase is miscompiled, because -fipa-pure-const discovers
that bar is const, but when sccvn during fre3 sees
# .MEM_140 = VDEF <.MEM_96>
*__pred$__d_43 = _50 (_49);
where _50 value numbers to &bar, it value numbers .MEM_140 to
vuse_ssa_val (gimple_vuse (stmt)). For const/pure calls that return
a SSA_NAME (or don't have lhs) that is fine, those calls don't store
anything, but if the lhs is present and not an SSA_NAME, value numbering
the vdef to anything but itself means that e.g. walk_non_aliased_vuses
won't consider the call, but the call acts as a store to its lhs.
When it is ignored, sccvn will return whatever has been stored to the
lhs earlier.
I've bootstrapped/regtested an earlier version of this patch, which did the
if (!lhs && gimple_call_lhs (stmt))
changed |= set_ssa_val_to (vdef, vdef);
part before else if (vnresult->result_vdef), and that regressed
+FAIL: gcc.dg/pr51879-16.c scan-tree-dump-times pre "foo \\\\(" 1
+FAIL: gcc.dg/pr51879-16.c scan-tree-dump-times pre "foo2 \\\\(" 1
so this updated patch uses result_vdef there as before and only otherwise
(which I think must be the const/pure case) decides based on whether the
lhs is non-SSA_NAME.
Ok for trunk if it passes another bootstrap/regtest?
2022-02-24 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/104601
* tree-ssa-sccvn.cc (visit_reference_op_call): For calls with
non-SSA_NAME lhs value number vdef to itself instead of e.g. the
vuse value number.
* g++.dg/torture/pr104601.C: New test.
--- gcc/tree-ssa-sccvn.cc.jj 2022-02-11 00:19:22.432063254 +0100
+++ gcc/tree-ssa-sccvn.cc 2022-02-24 09:43:39.715051959 +0100
@@ -5218,12 +5218,20 @@ visit_reference_op_call (tree lhs, gcall
if (vnresult)
{
- if (vnresult->result_vdef && vdef)
- changed |= set_ssa_val_to (vdef, vnresult->result_vdef);
- else if (vdef)
- /* If the call was discovered to be pure or const reflect
- that as far as possible. */
- changed |= set_ssa_val_to (vdef, vuse_ssa_val (gimple_vuse (stmt)));
+ if (vdef)
+ {
+ if (vnresult->result_vdef)
+ changed |= set_ssa_val_to (vdef, vnresult->result_vdef);
+ else if (!lhs && gimple_call_lhs (stmt))
+ /* If stmt has non-SSA_NAME lhs, value number the vdef to itself,
+ as the call still acts as a lhs store. */
+ changed |= set_ssa_val_to (vdef, vdef);
+ else
+ /* If the call was discovered to be pure or const reflect
+ that as far as possible. */
+ changed |= set_ssa_val_to (vdef,
+ vuse_ssa_val (gimple_vuse (stmt)));
+ }
if (!vnresult->result && lhs)
vnresult->result = lhs;
@@ -5248,7 +5256,11 @@ visit_reference_op_call (tree lhs, gcall
if (TREE_CODE (fn) == ADDR_EXPR
&& TREE_CODE (TREE_OPERAND (fn, 0)) == FUNCTION_DECL
&& (flags_from_decl_or_type (TREE_OPERAND (fn, 0))
- & (ECF_CONST | ECF_PURE)))
+ & (ECF_CONST | ECF_PURE))
+ /* If stmt has non-SSA_NAME lhs, value number the
+ vdef to itself, as the call still acts as a lhs
+ store. */
+ && (lhs || gimple_call_lhs (stmt) == NULL_TREE))
vdef_val = vuse_ssa_val (gimple_vuse (stmt));
}
changed |= set_ssa_val_to (vdef, vdef_val);
--- gcc/testsuite/g++.dg/torture/pr104601.C.jj 2022-02-23 16:23:52.437366019
+0100
+++ gcc/testsuite/g++.dg/torture/pr104601.C 2022-02-23 16:23:37.080578941
+0100
@@ -0,0 +1,32 @@
+// PR tree-optimization/104601
+// { dg-do run }
+// { dg-options "-std=c++17" }
+
+#include <algorithm>
+#include <optional>
+
+inline std::optional<int>
+foo (std::vector<int>::iterator b, std::vector<int>::iterator c,
+ std::optional<int> h (int))
+{
+ std::optional<int> d;
+ find_if (b, c, [&](auto e) { d = h(e); return d; });
+ return d;
+}
+
+std::optional<int>
+bar (int)
+{
+ return 1;
+}
+
+int
+main ()
+{
+ std::vector<int> g(10);
+ auto b = g.begin ();
+ auto c = g.end ();
+ auto e = foo (b, c, bar);
+ if (!e)
+ __builtin_abort ();
+}
Jakub
