On Thu, 24 Feb 2022, Jakub Jelinek wrote:
> 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?
OK.
Thanks,
Richard.
> 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
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
