pr43550 - remove unnecessary uxts in bswap

[Kugan]

Hi All,

For the bswap built-in, there are unnecessary uxts generated as reported
in pr43550. Can we rely on the argument being unsigned and set the
SUBREG promoted accordingly.

At least in ARM ABI, arguments are supposed to be properly zero/sign
extended.

Any thoughts?

Bootstrapped and regression tested on x86_64 and arm.

Thanks,
Kugan

gcc/testsuite
2014-09-05  Kugan Vivekanandarajah  <kug...@linaro.org>

        PR target/43550
        * gcc.target/arm/pr43550.c: New test.

gcc/
2014-09-05  Kugan Vivekanandarajah  <kug...@linaro.org>

        PR target/43550
        * builtins.c (expand_builtin_bswap): Generate promoted subreg.



diff --git a/gcc/builtins.c b/gcc/builtins.c
index e5a9b4d..a2f2358 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -4517,6 +4517,12 @@ expand_builtin_bswap (enum machine_mode target_mode, 
tree exp, rtx target,
   if (!validate_arglist (exp, INTEGER_TYPE, VOID_TYPE))
     return NULL_RTX;
 
+  if (!target
+      && (GET_MODE_PRECISION (word_mode)
+         > TYPE_PRECISION (TREE_TYPE (exp))))
+    target = gen_lowpart_SUBREG (TYPE_MODE (TREE_TYPE (exp)),
+                                  gen_reg_rtx (word_mode));
+
   arg = CALL_EXPR_ARG (exp, 0);
   op0 = expand_expr (arg,
                     subtarget && GET_MODE (subtarget) == target_mode
@@ -4528,8 +4534,13 @@ expand_builtin_bswap (enum machine_mode target_mode, 
tree exp, rtx target,
   target = expand_unop (target_mode, bswap_optab, op0, target, 1);
 
   gcc_assert (target);
-
-  return convert_to_mode (target_mode, target, 1);
+  target = convert_to_mode (target_mode, target, 1);
+  if (GET_CODE (target) == SUBREG)
+    {
+      SUBREG_PROMOTED_VAR_P (target) = 1;
+      SUBREG_PROMOTED_SET (target, SRP_UNSIGNED);
+    }
+  return target;
 }
 
 /* Expand a call to a unary builtin in EXP.
diff --git a/gcc/testsuite/gcc.target/arm/pr43550.c 
b/gcc/testsuite/gcc.target/arm/pr43550.c
index e69de29..7e4b2e0 100644
--- a/gcc/testsuite/gcc.target/arm/pr43550.c
+++ b/gcc/testsuite/gcc.target/arm/pr43550.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-final { scan-assembler-times "uxt" 0 } } */
+
+typedef unsigned short uint16_t;
+typedef unsigned int uint32_t;
+
+uint16_t s16 (uint16_t v)
+{
+  return v >> 8 | v << 8;
+}
+
+uint16_t _s16 (uint16_t v)
+{
+  return __builtin_bswap16 (v);
+}
+
+uint32_t s32 (uint32_t v)
+{
+  return __builtin_bswap32 (v);
+}