x86: Transform to "pushq $-1; popq reg" for -Oz

commit 4c80062d7b8c272e2e193b8074a8440dbb4fe588
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Sun May 25 07:40:29 2025 +0800

    x86: Enable *mov<mode>_(and|or) only for -Oz

disabled transformation from "movq $-1,reg" to "pushq $-1; popq reg" for
-Oz.  But for legacy integer registers, the former is 4 bytes and the
latter is 3 bytes.  Enable such transformation for -Oz.

gcc/

	PR target/120427
	* config/i386/i386.md (peephole2): Transform "movq $-1,reg" to
	"pushq $-1; popq reg" for -Oz if reg is a legacy integer register.

gcc/testsuite/

	PR target/120427
	* gcc.target/i386/pr120427-5.c: New test.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit 71dae74158d05b75e367629ce21da3f0a2945576)

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 1d33ba0108eb9773ad4067625a1c36cb0e1166aa..de9829bc3b6240d79132eb313daa8ce0573100b4 100644 (file)
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -2957,7 +2957,8 @@
        (match_operand:SWI248 1 "const_int_operand"))]
   "optimize_insn_for_size_p () && optimize_size > 1
    && operands[1] != const0_rtx
-   && operands[1] != constm1_rtx
+   && (operands[1] != constm1_rtx
+       || (<MODE>mode == DImode && LEGACY_INT_REG_P (operands[0])))
    && IN_RANGE (INTVAL (operands[1]), -128, 127)
    && !ix86_red_zone_used
    && REGNO (operands[0]) != SP_REG"

diff --git a/gcc/testsuite/gcc.target/i386/pr120427-5.c b/gcc/testsuite/gcc.target/i386/pr120427-5.c
new file mode 100644 (file)
index 0000000..7199aef
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr120427-5.c
@@ -0,0 +1,10 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-Oz" } */
+
+long long
+func1 (void)
+{
+  return -1;
+}
+/* { dg-final { scan-assembler-times "pushq\[ \\t\]+\\\$-1" 1 } } */
+/* { dg-final { scan-assembler-times "popq\[ \\t\]+%rax" 1 } } */