PATCH [3/n]: Prepare x32: PR rtl-optimization/49088: Combine fails to properly handle zero-extension and signed int constant

[H.J. Lu]

See:

http://gcc.gnu.org/ml/gcc-patches/2011-05/msg02150.html

for an analysis.  OK for trunk?

Thanks.


H.J.
---
2011-05-21  H.J. Lu  <hongjiu...@intel.com>

        PR rtl-optimization/49088
        * combine.c (force_to_mode): If X is narrower than MODE and we
        want all the bits in X's mode, just use the operand when it
        is CONST_INT.

diff --git a/gcc/combine.c b/gcc/combine.c
index 8af86f2..710fe0e 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -8321,8 +8321,26 @@ force_to_mode (rtx x, enum machine_mode mode, unsigned 
HOST_WIDE_INT mask,
       /* For most binary operations, just propagate into the operation and
         change the mode if we have an operation of that mode.  */
 
-      op0 = force_to_mode (XEXP (x, 0), mode, mask, next_select);
-      op1 = force_to_mode (XEXP (x, 1), mode, mask, next_select);
+      /* If X is narrower than MODE and we want all the bits in X's
+        mode, just use the operand when it is CONST_INT.  */
+      if (SCALAR_INT_MODE_P (mode)
+         && GET_MODE_SIZE (GET_MODE (x)) < GET_MODE_SIZE (mode)
+         && (GET_MODE_MASK (GET_MODE (x)) & ~mask) == 0)
+       {
+         if (CONST_INT_P (XEXP (x, 0)))
+           op0 = XEXP (x, 0);
+         else
+           op0 = force_to_mode (XEXP (x, 0), mode, mask, next_select);
+         if (CONST_INT_P (XEXP (x, 1)))
+           op1 = XEXP (x, 1);
+         else
+           op1 = force_to_mode (XEXP (x, 1), mode, mask, next_select);
+       }
+      else
+       {
+         op0 = force_to_mode (XEXP (x, 0), mode, mask, next_select);
+         op1 = force_to_mode (XEXP (x, 1), mode, mask, next_select);
+       }
 
       /* If we ended up truncating both operands, truncate the result of the
         operation instead.  */