[PATCH v3] i386: Disable ix86_expand_vecop_qihi2 when !TARGET_AVX512BW

[Haochen Jiang <haochen.jiang@intel.com>]

Hi all,

This is the v3 patch to fix PR115069. The new testcase has passed.

Changes in v3:
  - Simplify the testcase.

Changes in v2:
  - Add a testcase.
  - Change the comment for the early exit.

Thx,
Haochen

Since vpermq is really slow, we should avoid using it for permutation
when vpmovwb is not available (needs AVX512BW) for ix86_expand_vecop_qihi2
and fall back to ix86_expand_vecop_qihi.

gcc/ChangeLog:

        PR target/115069
	* config/i386/i386-expand.cc (ix86_expand_vecop_qihi2):
	Do not enable the optimization when AVX512BW is not enabled.

gcc/testsuite/ChangeLog:

        PR target/115069
	* gcc.target/i386/pr115069.c: New.
---
 gcc/config/i386/i386-expand.cc           |  7 +++++++
 gcc/testsuite/gcc.target/i386/pr115069.c | 10 ++++++++++
 2 files changed, 17 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr115069.c

diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
index a6132911e6a..f7939761879 100644
--- a/gcc/config/i386/i386-expand.cc
+++ b/gcc/config/i386/i386-expand.cc
@@ -24323,6 +24323,13 @@ ix86_expand_vecop_qihi2 (enum rtx_code code, rtx dest, rtx op1, rtx op2)
   bool op2vec = GET_MODE_CLASS (GET_MODE (op2)) == MODE_VECTOR_INT;
   bool uns_p = code != ASHIFTRT;
 
+  /* Without VPMOVWB (provided by AVX512BW ISA), the expansion uses the
+     generic permutation to merge the data back into the right place.  This
+     permutation results in VPERMQ, which is slow, so better fall back to
+     ix86_expand_vecop_qihi.  */
+  if (!TARGET_AVX512BW)
+    return false;
+
   if ((qimode == V16QImode && !TARGET_AVX2)
       || (qimode == V32QImode && (!TARGET_AVX512BW || !TARGET_EVEX512))
       /* There are no V64HImode instructions.  */
diff --git a/gcc/testsuite/gcc.target/i386/pr115069.c b/gcc/testsuite/gcc.target/i386/pr115069.c
new file mode 100644
index 00000000000..7f1ff209f26
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr115069.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mavx2" } */
+/* { dg-final { scan-assembler-not "vpermq" } } */
+
+typedef char v16qi __attribute__((vector_size(16)));
+
+v16qi foo (v16qi a, v16qi b) {
+    return a * b;
+}
+
-- 
2.31.1