[PATCH] x32: Encode %esp as %rsp to avoid 0x67 prefix

[H.J. Lu]

Since the upper 32 bits of stack register are always zero for x32, we
can encode %esp as %rsp to avoid 0x67 prefix in address if there is no
index or base register.

Tested on x86-64.  OK for trunk?

H.J.
----
gcc/

        PR target/82267
        * config/i386/i386.c (ix86_print_operand_address_as): Encode
        %esp as %rsp to avoid 0x67 prefix if there is no index or base
        register.

gcc/testsuite/

        PR target/82267
        * gcc.target/i386/pr82267.c: New tests.
---
 gcc/config/i386/i386.c                  | 17 +++++++++++++++++
 gcc/testsuite/gcc.target/i386/pr82267.c | 14 ++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr82267.c

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 5e8f58c5e9f..519fdb0ffae 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -19849,6 +19849,23 @@ ix86_print_operand_address_as (FILE *file, rtx addr,
   disp = parts.disp;
   scale = parts.scale;
 
+  /* Since the upper 32 bits of RSP are always zero for x32, we can
+     encode %esp as %rsp to avoid 0x67 prefix if there is no index or
+     base register.  */
+  if (TARGET_X32
+      && Pmode == SImode
+      && (!index || !base)
+      && index != base)
+    {
+      if (base)
+       {
+         if (REGNO (base) == SP_REG)
+           base = gen_rtx_REG (DImode, SP_REG);
+       }
+      else if (REGNO (index) == SP_REG)
+       index = gen_rtx_REG (DImode, SP_REG);
+    }
+
   if (ADDR_SPACE_GENERIC_P (as))
     as = parts.seg;
   else
diff --git a/gcc/testsuite/gcc.target/i386/pr82267.c 
b/gcc/testsuite/gcc.target/i386/pr82267.c
new file mode 100644
index 00000000000..5e4b271d41d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr82267.c
@@ -0,0 +1,14 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-require-effective-target maybe_x32 } */
+/* { dg-options "-O2 -mx32 -maddress-mode=short" } */
+
+int
+stackuse (void)
+{
+  volatile int foo = 2;
+  return foo * 3;
+}
+
+/* Verify we that use %rsp to access stack.  */
+/* { dg-final { scan-assembler-not "%esp" } } */
+/* { dg-final { scan-assembler "%rsp" } } */
-- 
2.13.5