The following makes FRE optimize a load we formerly required
SRA + CCP for which now run after we get rid of all __builtin_constant_p
calls.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
2021-03-15 Richard Biener <rguent...@suse.de>
PR tree-optimization/98834
* tree-ssa-sccvn.c (vn_reference_lookup_3): Handle missing
subsetting by truncating the access size.
* g++.dg/opt/pr98834.C: New testcase.
---
gcc/testsuite/g++.dg/opt/pr98834.C | 71 ++++++++++++++++++++++++++++++
gcc/tree-ssa-sccvn.c | 12 ++++-
2 files changed, 82 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/opt/pr98834.C
diff --git a/gcc/testsuite/g++.dg/opt/pr98834.C
b/gcc/testsuite/g++.dg/opt/pr98834.C
new file mode 100644
index 00000000000..fafd3227181
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr98834.C
@@ -0,0 +1,71 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target c++17 } */
+/* { dg-options "-O2 -fdump-tree-fre3" } */
+
+struct _Base
+{
+ int _M_data = 0;
+};
+
+struct _Wrapper : _Base
+{
+ _Wrapper(int) {}
+
+ bool _M_is_constprop() { return __builtin_constant_p(_M_data); }
+};
+
+struct _Impl
+{
+ _Wrapper _S_multiplies(_Wrapper __x, _Wrapper __y)
+ {
+ if (__x._M_is_constprop() || __y._M_is_constprop())
+ return __y;
+ return 0;
+ }
+};
+
+struct _TupleData
+{
+ _Wrapper first;
+ int second;
+};
+
+struct _Tuple : _TupleData
+{
+ template <typename _Fp>
+ _Tuple _M_apply_per_chunk(_Fp __fun, _Tuple __y)
+ {
+ return {__fun(first, __y.first), second};
+ }
+};
+
+struct _ImplFixed
+{
+ static _Tuple _S_multiplies(_Tuple __x, _Tuple __y)
+ {
+ return __x._M_apply_per_chunk(
+ []( auto __xx, auto __yy) {
+ return _Impl()._S_multiplies(__xx, __yy);
+ },
+ __y);
+ }
+};
+
+class simd
+{
+public:
+ [[__gnu__::__always_inline__]] friend simd operator*(simd __x, simd __y)
+ { return _ImplFixed::_S_multiplies(__x._M_data, __y._M_data); }
+
+ simd(_Tuple __init) : _M_data(__init) {}
+
+ _Tuple _M_data;
+};
+
+int main()
+{
+ simd({0, 0}) * simd({0, 0});
+}
+
+/* FRE3 should elide all conditionals in the remaining main. */
+/* { dg-final { scan-tree-dump-times "<bb" 1 "fre3" } } */
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 65b3967b9e1..99759a8744a 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -3215,7 +3215,17 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void
*data_,
return (void *)-1;
/* This can happen with bitfields. */
if (maybe_ne (ref->size, r.size))
- return (void *)-1;
+ {
+ /* If the access lacks some subsetting simply apply that by
+ shortening it. That in the end can only be successful
+ if we can pun the lookup result which in turn requires
+ exact offsets. */
+ if (known_eq (r.size, r.max_size)
+ && known_lt (ref->size, r.size))
+ r.size = r.max_size = ref->size;
+ else
+ return (void *)-1;
+ }
*ref = r;
/* Do not update last seen VUSE after translating. */
--
2.26.2
