Simplifies (x << c) >> c where x is a signed integral type of
width >= int and c = precision(type) - 1 into -(x & 1). Tested successfully
on x86_64 and x86 targets.
PR middle-end/101955
gcc/ChangeLog:
* match.pd (x << c) >> c -> -(x & 1): New simplification.
gcc/testsuite/ChangeLog:
* gcc.dg/pr101955.c: New test.
---
gcc/match.pd | 10 +++++
gcc/testsuite/gcc.dg/pr101955.c | 69 +++++++++++++++++++++++++++++++++
2 files changed, 79 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/pr101955.c
diff --git a/gcc/match.pd b/gcc/match.pd
index 8543f777a28..820fc890e8e 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3766,6 +3766,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
&& (wi::ltu_p (wi::to_wide (@1), element_precision (type))))
(bit_and @0 (rshift { build_minus_one_cst (type); } @1))))
+/* Optimize (X << C) >> C where C = precision(type) - 1 and X is signed
+ into -(X & 1). */
+(simplify
+ (rshift (nop_convert? (lshift @0 uniform_integer_cst_p@1)) @@1)
+ (with { tree cst = uniform_integer_cst_p (@1); }
+ (if (ANY_INTEGRAL_TYPE_P (type)
+ && !TYPE_UNSIGNED (type)
+ && wi::eq_p (wi::to_wide (cst), element_precision (type) - 1))
+ (negate (bit_and (convert @0) { build_one_cst (type); })))))
+
/* Optimize x >> x into 0 */
(simplify
(rshift @0 @0)
diff --git a/gcc/testsuite/gcc.dg/pr101955.c b/gcc/testsuite/gcc.dg/pr101955.c
new file mode 100644
index 00000000000..386154911c5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101955.c
@@ -0,0 +1,69 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-dse1 -Wno-psabi" } */
+
+typedef int v4si __attribute__((vector_size(4 * sizeof(int))));
+
+__attribute__((noipa)) int
+t1 (int x)
+{
+ return (x << 31) >> 31;
+}
+
+__attribute__((noipa)) int
+t2 (int x)
+{
+ int y = x << 31;
+ int z = y >> 31;
+ return z;
+}
+
+__attribute__((noipa)) int
+t3 (int x)
+{
+ int w = 31;
+ int y = x << w;
+ int z = y >> w;
+ return z;
+}
+
+__attribute__((noipa)) long long
+t4 (long long x)
+{
+ return (x << 63) >> 63;
+}
+
+__attribute__((noipa)) long long
+t5 (long long x)
+{
+ long long y = x << 63;
+ long long z = y >> 63;
+ return z;
+}
+
+__attribute__((noipa)) long long
+t6 (long long x)
+{
+ int w = 63;
+ long long y = x << w;
+ long long z = y >> w;
+ return z;
+}
+
+__attribute__((noipa)) v4si
+t7 (v4si x)
+{
+ return (x << 31) >> 31;
+}
+
+__attribute__((noipa)) v4si
+t8 (v4si x)
+{
+ v4si t = {31,31,31,31};
+ return (x << t) >> t;
+}
+
+/* { dg-final { scan-tree-dump-not " >> " "dse1" } } */
+/* { dg-final { scan-tree-dump-not " << " "dse1" } } */
+/* { dg-final { scan-tree-dump-times " -" 8 "dse1" } } */
+/* { dg-final { scan-tree-dump-times " & " 8 "dse1" } } */
+
--
2.39.3
