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* [gcc r11-3743] match.pd: Fix up FFS -> CTZ + 1 optimization [PR97325]
@ 2020-10-09 8:18 Jakub Jelinek
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From: Jakub Jelinek @ 2020-10-09 8:18 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:600cf1128e49f086522bfddc54490b4e39e30383
commit r11-3743-g600cf1128e49f086522bfddc54490b4e39e30383
Author: Jakub Jelinek <jakub@redhat.com>
Date: Fri Oct 9 10:16:57 2020 +0200
match.pd: Fix up FFS -> CTZ + 1 optimization [PR97325]
And no testcase was included, I'm including one below.
Anyway, this PR and the other CTZ related discussions led me to discover a
bug I've made earlier, CLZ/CTZ builtins have unsigned arguments and e.g.
both the vr-values.cc and now gimple-range.cc code heavily relies on that,
but __builtin_ffs has a signed operand and this optimization was incorrectly
making the operand signed too, so I guess it would greatly confuse VRP in
some cases.
2020-10-09 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/97325
* match.pd (FFS(nonzero) -> CTZ(nonzero) + 1): Cast argument to
corresponding unsigned type.
* gcc.c-torture/execute/pr97325.c: New test.
Diff:
---
gcc/match.pd | 3 ++-
gcc/testsuite/gcc.c-torture/execute/pr97325.c | 15 +++++++++++++++
2 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/gcc/match.pd b/gcc/match.pd
index 952643f3c6d..a7032dcae29 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -6196,7 +6196,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
&& direct_internal_fn_supported_p (IFN_CTZ, TREE_TYPE (@0),
OPTIMIZE_FOR_SPEED))
- (plus (CTZ:type @0) { build_one_cst (type); })))
+ (with { tree utype = unsigned_type_for (TREE_TYPE (@0)); }
+ (plus (CTZ:type (convert:utype @0)) { build_one_cst (type); }))))
#endif
(for ffs (BUILT_IN_FFS BUILT_IN_FFSL BUILT_IN_FFSLL
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr97325.c b/gcc/testsuite/gcc.c-torture/execute/pr97325.c
new file mode 100644
index 00000000000..f734c85c711
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr97325.c
@@ -0,0 +1,15 @@
+/* PR tree-optimization/97325 */
+
+unsigned long long
+foo (unsigned long long c)
+{
+ return c ? __builtin_ffs (-(unsigned short) c) : 0;
+}
+
+int
+main ()
+{
+ if (foo (2) != 2)
+ __builtin_abort ();
+ return 0;
+}
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