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tree-optimization/106922 - extend same-val clobber FRE

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The following extends the skipping of same valued stores to
handle an arbitrary number of them as long as they are from the
same value (which we now record).  That's an obvious extension
which allows to optimize the m_engaged member of std::optional
more reliably.

	PR tree-optimization/106922
	* tree-ssa-sccvn.cc (vn_reference_lookup_3): Allow
	an arbitrary number of same valued skipped stores.

	* g++.dg/torture/pr106922.C: New testcase.
This commit is contained in:
Richard Biener 2022-09-23 14:28:52 +02:00
parent ab0f70a630
commit af611afe5f
2 changed files with 55 additions and 3 deletions
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48
gcc/testsuite/g++.dg/torture/pr106922.C Normal file
View file

@ -0,0 +1,48 @@
// { dg-do compile }
// { dg-require-effective-target c++17 }
// { dg-additional-options "-Wall" }
// -O1 doesn't iterate VN and thus has bogus uninit diagnostics
// { dg-skip-if "" { *-*-* } { "-O1" } { "" } }
#include <vector>
#include <optional>
template <class T>
using Optional = std::optional<T>;
#include <sstream>
struct MyOptionalStructWithInt {
int myint; /* works without this */
Optional<std::vector<std::string>> myoptional;
};
struct MyOptionalsStruct {
MyOptionalStructWithInt external1;
MyOptionalStructWithInt external2;
};
struct MyStruct { };
std::ostream &operator << (std::ostream &os, const MyStruct &myStruct);
std::vector<MyStruct> getMyStructs();
void test()
{
MyOptionalsStruct externals;
MyOptionalStructWithInt internal1;
MyOptionalStructWithInt internal2;
std::vector<MyStruct> myStructs;
myStructs = getMyStructs();
for (const auto& myStruct : myStructs)
{
std::stringstream address_stream;
address_stream << myStruct;
internal1.myint = internal2.myint = 0;
externals.external1 = internal1;
externals.external2 = internal2;
externals.external2 = internal2;
}
}

10
gcc/tree-ssa-sccvn.cc
View file

@ -2680,7 +2680,6 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
if (is_gimple_reg_type (TREE_TYPE (lhs))
&& types_compatible_p (TREE_TYPE (lhs), vr->type)
&& (ref->ref || data->orig_ref.ref)
&& !data->same_val
&& !data->mask
&& data->partial_defs.is_empty ()
&& multiple_p (get_object_alignment
@ -2693,8 +2692,13 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
a different loop iteration but only to loop invariants. Use
CONSTANT_CLASS_P (unvalueized!) as conservative approximation.
The one-hop lookup below doesn't have this issue since there's
a virtual PHI before we ever reach a backedge to cross. */
if (CONSTANT_CLASS_P (rhs))
a virtual PHI before we ever reach a backedge to cross.
We can skip multiple defs as long as they are from the same
value though. */
if (data->same_val
&& !operand_equal_p (data->same_val, rhs))
;
else if (CONSTANT_CLASS_P (rhs))
{
if (dump_file && (dump_flags & TDF_DETAILS))
{