PATCH: PR rtl-optimization/49088: Combine fails to properly handle zero-extension and signed int constant

[H.J. Lu]

Hi,

When combine sees:

(insn 5 2 7 2 (parallel [
            (set (reg/f:DI 61)
                (plus:DI (reg/f:DI 20 frame)
                    (const_int -64 [0xffffffffffffffc0])))
            (clobber (reg:CC 17 flags))
        ]) x.i:12 252 {*adddi_1}
     (expr_list:REG_UNUSED (reg:CC 17 flags)
        (nil)))
(insn 17 9 18 2 (parallel [
            (set (reg:SI 72)
                (plus:SI (subreg:SI (reg/f:DI 61) 0)
                    (const_int 6 [0x6])))
            (clobber (reg:CC 17 flags))
        ]) x.i:14 251 {*addsi_1}
     (expr_list:REG_DEAD (reg/f:DI 61)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

(insn 18 17 10 2 (set (reg:DI 73)
        (zero_extend:DI (reg:SI 72))) x.i:14 112
{*zero_extendsidi2_rex64}
     (expr_list:REG_DEAD (reg:SI 72)
        (nil)))

(insn 11 10 12 2 (set (reg:DI 68)
        (reg:DI 73)) x.i:14 62 {*movdi_internal_rex64}
     (expr_list:REG_DEAD (reg:DI 73)
        (nil)))

it was turned into

(insn 18 17 10 2 (set (reg:DI 73) 
        (const_int 4294967238 [0xffffffc6])) x.i:14 62
{*movdi_internal_rex64}
     (nil))

(insn 11 10 12 2 (set (reg:DI 68)
        (plus:DI (reg/f:DI 20 frame)
            (reg:DI 73))) x.i:14 247 {*lea_1}
     (expr_list:REG_DEAD (reg:DI 73)
        (nil)))

force_to_mode has

  /* If X is a CONST_INT, return a new one.  Do this here since the
     test below will fail.  */
  if (CONST_INT_P (x))
    {
      if (SCALAR_INT_MODE_P (mode))
        return gen_int_mode (INTVAL (x) & mask, mode);
      else  
        {     
          x = GEN_INT (INTVAL (x) & mask);
          return gen_lowpart_common (mode, x);
        }     
    }

 /* If X is narrower than MODE and we want all the bits in X's mode, just
     get X in the proper mode.  */
  if (GET_MODE_SIZE (GET_MODE (x)) < GET_MODE_SIZE (mode)
      && (GET_MODE_MASK (GET_MODE (x)) & ~mask) == 0) 
    return gen_lowpart (mode, x);

When it gets

(zero_extend:DI (plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
        (const_int -58 [0xffffffffffffffc6])))

It first sets mask to 32bit and leads to

(subreg:DI (plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
        (const_int -58 [0xffffffffffffffc6])) 0)

with mask == 0xffffffff.  The probem is

    binop:
      /* 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);

where it calls force_to_mode with -58, 0xffffffff mask and DImode.  This
transformation is incorrect.  This patch changes mask to MODE_MASK of
mode if all the bits in CONST_INT are used.  OK for trunk?

Thanks.


H.J.
---
commit 3a590e037128ba64d74fb7b323d2a4d19a02248f
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Sat May 21 06:20:09 2011 -0700

    Properly handle CONST_INT operands.
    
    2011-05-21  H.J. Lu  <hongjiu.lu@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/ChangeLog.x32 b/gcc/ChangeLog.x32
index abd57a4..bf844ea 100644
--- a/gcc/ChangeLog.x32
+++ b/gcc/ChangeLog.x32
@@ -1,3 +1,10 @@
+2011-05-21  H.J. Lu  <hongjiu.lu@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.
+
 2011-05-20  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/48529
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.  */