i386: Support read-modify-write memory operands in STV.

This patch enables STV when the first operand of a TImode binary
logic operand (AND, IOR or XOR) is a memory operand, which is commonly
the case with read-modify-write instructions.

A different motivating example from the one given previously is:

__int128 m, p, q;
void foo() {
    m ^= (p & q);
}

Currently with -O2 -mavx the RMW instructions are rejected by STV,
resulting in scalar code:

foo:	movq    p(%rip), %rax
        movq    p+8(%rip), %rdx
        andq    q(%rip), %rax
        andq    q+8(%rip), %rdx
        xorq    %rax, m(%rip)
        xorq    %rdx, m+8(%rip)
        ret

With this patch they become scalar-to-vector candidates:

foo:	vmovdqa p(%rip), %xmm0
        vpand   q(%rip), %xmm0, %xmm0
        vpxor   m(%rip), %xmm0, %xmm0
        vmovdqa %xmm0, m(%rip)
        ret

2024-08-31  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386-features.cc (timode_scalar_to_vector_candidate_p):
	Support the first operand of AND, IOR and XOR being MEM_P, i.e. a
	read-modify-write insn.

gcc/testsuite/ChangeLog
	* gcc.target/i386/movti-2.c: Change dg-options to -Os.
	* gcc.target/i386/movti-4.c: Expected output of original movti-2.c.

diff --git a/gcc/config/i386/i386-features.cc b/gcc/config/i386/i386-features.cc
index c09a5c73a8e39f0691f32b6ad0772adc58e7085a..3434d006943958dd6bbb8c2a0fe9f3728589ada3 100644 (file)
--- a/gcc/config/i386/i386-features.cc
+++ b/gcc/config/i386/i386-features.cc
@@ -2330,14 +2330,16 @@ timode_scalar_to_vector_candidate_p (rtx_insn *insn)
              || CONST_SCALAR_INT_P (XEXP (src, 1))
              || timode_mem_p (XEXP (src, 1))))
        return true;
-      return REG_P (XEXP (src, 0))
+      return (REG_P (XEXP (src, 0))
+             || timode_mem_p (XEXP (src, 0)))
             && (REG_P (XEXP (src, 1))
                 || CONST_SCALAR_INT_P (XEXP (src, 1))
                 || timode_mem_p (XEXP (src, 1)));
 
     case IOR:
     case XOR:
-      return REG_P (XEXP (src, 0))
+      return (REG_P (XEXP (src, 0))
+             || timode_mem_p (XEXP (src, 0)))
             && (REG_P (XEXP (src, 1))
                 || CONST_SCALAR_INT_P (XEXP (src, 1))
                 || timode_mem_p (XEXP (src, 1)));

diff --git a/gcc/testsuite/gcc.target/i386/movti-2.c b/gcc/testsuite/gcc.target/i386/movti-2.c
index 73f69d290cbdf9dff3f97d9935ea0469996acffa..c3a6ae3c51de055de173ece00a9df1bd06eceaff 100644 (file)
--- a/gcc/testsuite/gcc.target/i386/movti-2.c
+++ b/gcc/testsuite/gcc.target/i386/movti-2.c
@@ -1,5 +1,5 @@
 /* { dg-do compile { target int128 } } */
-/* { dg-options "-O2 -mavx" } */
+/* { dg-options "-Os -mavx" } */
 __int128 m;
 
 void foo()

diff --git a/gcc/testsuite/gcc.target/i386/movti-4.c b/gcc/testsuite/gcc.target/i386/movti-4.c
new file mode 100644 (file)
index 0000000..eac66fc
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/movti-4.c
@@ -0,0 +1,11 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2 -mavx" } */
+__int128 m;
+
+void foo()
+{
+    m &= ((__int128)0x0123456789abcdefULL<<64) | 0x0123456789abcdefULL;
+}
+
+/* { dg-final { scan-assembler-times "movabsq" 1 } } */
+/* { dg-final { scan-assembler-times "vpand" 1 } } */