re PR target/27971 (eliminate shift in array[(x>>2)&3])

gcc/ChangeLog
       PR rtl-optimization/27971
       * combine.c (find_split_point): introduced a new split for certain
       types of mem rtx.

gcc/testsuite/ChangeLog

       PR rtl-optimization/27971
       * gcc.target/i386/pr27971.c: New testcase.

From-SVN: r131460

gcc/ChangeLog

+2008-01-10  Raksit Ashok  <raksit@google.com>
+
+	PR rtl-optimization/27971
+	* combine.c (find_split_point): introduced a new split for certain
+	types of mem rtx.
+
 2008-01-10  DJ Delorie  <dj@redhat.com>
 
 	* config/m32c/m32c.c (m32c_hard_regno_nregs_1): Renamed from...

gcc/combine.c

@@ -3967,6 +3967,15 @@ find_split_point (rtx *loc, rtx insn)
 			 && OBJECT_P (SUBREG_REG (XEXP (XEXP (x, 0), 0)))))
 	    return &XEXP (XEXP (x, 0), 0);
 	}
+
+      /* If we have a PLUS whose first operand is complex, try computing it
+         separately by making a split there.  */
+      if (GET_CODE (XEXP (x, 0)) == PLUS
+          && ! memory_address_p (GET_MODE (x), XEXP (x, 0))
+          && ! OBJECT_P (XEXP (XEXP (x, 0), 0))
+          && ! (GET_CODE (XEXP (XEXP (x, 0), 0)) == SUBREG
+                && OBJECT_P (SUBREG_REG (XEXP (XEXP (x, 0), 0)))))
+        return &XEXP (XEXP (x, 0), 0);
       break;
 
     case SET:

gcc/testsuite/ChangeLog

+2008-01-10  Raksit Ashok  <raksit@google.com>
+
+	PR rtl-optimization/27971
+	* gcc.target/i386/pr27971.c: New testcase.
+
 2008-01-10  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/34396

gcc/testsuite/gcc.target/i386/pr27971.c

+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+unsigned array[4];
+
+unsigned foo(unsigned long x)
+{
+          return array[(x>>2)&3ul];
+}
+
+/* { dg-final { scan-assembler-not "shr\[^\\n\]*2" } } */
+/* { dg-final { scan-assembler "and\[^\\n\]*12" } } */