[committed] aarch64: Improve vcombine codegen [PR89057]

[committed] aarch64: Improve vcombine codegen [PR89057]

[Richard Sandiford]

This patch fixes a codegen regression in the handling of things like:

  __temp.val[0]								     \
    = vcombine_##funcsuffix (__b.val[0],				     \
			     vcreate_##funcsuffix (__AARCH64_UINT64_C (0))); \

in the 64-bit vst[234] functions.  The zero was forced into a
register at expand time, and we relied on combine to fuse the
zero and combine back together into a single combinez pattern.
The problem is that the zero could be hoisted before combine
gets a chance to do its thing.

Tested on aarch64-linux-gnu and aarch64_be-elf.  Pushed to trunk so far.
Since it's a regression from GCC 7, I'll backport as far it can go
without modification.

Richard


gcc/
	PR target/89057
	* config/aarch64/aarch64-simd.md (aarch64_combine<mode>): Accept
	aarch64_simd_reg_or_zero for operand 2.  Use the combinez patterns
	to handle zero operands.

gcc/testsuite/
	PR target/89057
	* gcc.target/aarch64/pr89057.c: New test.
---
 gcc/config/aarch64/aarch64-simd.md         | 15 ++++++++++++---
 gcc/testsuite/gcc.target/aarch64/pr89057.c | 16 ++++++++++++++++
 2 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/pr89057.c

diff --git a/gcc/config/aarch64/aarch64-simd.md b/gcc/config/aarch64/aarch64-simd.md
index c4e3b896295..85770c84f0a 100644
--- a/gcc/config/aarch64/aarch64-simd.md
+++ b/gcc/config/aarch64/aarch64-simd.md
@@ -3340,11 +3340,20 @@ (define_insn "@aarch64_combinez_be<mode>"
 (define_expand "aarch64_combine<mode>"
   [(match_operand:<VDBL> 0 "register_operand")
    (match_operand:VDC 1 "register_operand")
-   (match_operand:VDC 2 "register_operand")]
+   (match_operand:VDC 2 "aarch64_simd_reg_or_zero")]
   "TARGET_SIMD"
 {
-  aarch64_split_simd_combine (operands[0], operands[1], operands[2]);
-
+  if (operands[2] == CONST0_RTX (<MODE>mode))
+    {
+      if (BYTES_BIG_ENDIAN)
+	emit_insn (gen_aarch64_combinez_be<mode> (operands[0], operands[1],
+						  operands[2]));
+      else
+	emit_insn (gen_aarch64_combinez<mode> (operands[0], operands[1],
+					       operands[2]));
+    }
+  else
+    aarch64_split_simd_combine (operands[0], operands[1], operands[2]);
   DONE;
 }
 )
diff --git a/gcc/testsuite/gcc.target/aarch64/pr89057.c b/gcc/testsuite/gcc.target/aarch64/pr89057.c
new file mode 100644
index 00000000000..1e200245ddd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr89057.c
@@ -0,0 +1,16 @@
+/* { dg-options "-O3" } */
+
+#include <arm_neon.h>
+
+void
+f (int32_t *dst, int32_t *src, int n)
+{
+  for (int i = 0; i < n; ++i)
+    {
+      int32x2x3_t a = vld3_s32 (src + i * 6);
+      int32x2x3_t b = { a.val[2], a.val[1], a.val[0] };
+      vst3_s32 (dst + i * 6, b);
+    }
+}
+
+/* { dg-final { scan-assembler-not {\tins\t} } } */