re PR rtl-optimization/45617 (optimize bit shift+compare at RTL level)

	PR rtl-optimization/45617
	* combine.c (simplify_comparison): Optimize (X >> N) {>,>=,<,<=} C
	even if low N bits of X aren't known to be zero.

	* gcc.target/i386/pr45617.c: New test.

From-SVN: r164257

gcc/ChangeLog

+2010-09-13  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/45617
+	* combine.c (simplify_comparison): Optimize (X >> N) {>,>=,<,<=} C
+	even if low N bits of X aren't known to be zero.
+
 2010-09-13  H.J. Lu  <hongjiu.lu@intel.com>
 
 	* config/i386/i386-protos.h (ix86_units_per_simd_word): New.

gcc/combine.c

@@ -11773,13 +11773,14 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
 	  /* If we have (compare (xshiftrt FOO N) (const_int C)) and
 	     the low order N bits of FOO are known to be zero, we can do this
 	     by comparing FOO with C shifted left N bits so long as no
-	     overflow occurs.  */
+	     overflow occurs.  Even if the low order N bits of FOO aren't known
+	     to be zero, if the comparison is >= or < we can use the same
+	     optimization and for > or <= by setting all the low
+	     order N bits in the comparison constant.  */
 	  if (CONST_INT_P (XEXP (op0, 1))
-	      && INTVAL (XEXP (op0, 1)) >= 0
+	      && INTVAL (XEXP (op0, 1)) > 0
 	      && INTVAL (XEXP (op0, 1)) < HOST_BITS_PER_WIDE_INT
 	      && mode_width <= HOST_BITS_PER_WIDE_INT
-	      && (nonzero_bits (XEXP (op0, 0), mode)
-		  & (((HOST_WIDE_INT) 1 << INTVAL (XEXP (op0, 1))) - 1)) == 0
 	      && (((unsigned HOST_WIDE_INT) const_op
 		   + (GET_CODE (op0) != LSHIFTRT
 		      ? ((GET_MODE_MASK (mode) >> INTVAL (XEXP (op0, 1)) >> 1)
@@ -11787,15 +11788,27 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
 		      : 0))
 		  <= GET_MODE_MASK (mode) >> INTVAL (XEXP (op0, 1))))
 	    {
-	      /* If the shift was logical, then we must make the condition
-		 unsigned.  */
-	      if (GET_CODE (op0) == LSHIFTRT)
-		code = unsigned_condition (code);
-
-	      const_op <<= INTVAL (XEXP (op0, 1));
-	      op1 = GEN_INT (const_op);
-	      op0 = XEXP (op0, 0);
-	      continue;
+	      unsigned HOST_WIDE_INT low_bits
+		= (nonzero_bits (XEXP (op0, 0), mode)
+		   & (((unsigned HOST_WIDE_INT) 1
+		       << INTVAL (XEXP (op0, 1))) - 1));
+	      if (low_bits == 0 || !equality_comparison_p)
+		{
+		  /* If the shift was logical, then we must make the condition
+		     unsigned.  */
+		  if (GET_CODE (op0) == LSHIFTRT)
+		    code = unsigned_condition (code);
+
+		  const_op <<= INTVAL (XEXP (op0, 1));
+		  if (low_bits != 0
+		      && (code == GT || code == GTU
+			  || code == LE || code == LEU))
+		    const_op
+		      |= (((HOST_WIDE_INT) 1 << INTVAL (XEXP (op0, 1))) - 1);
+		  op1 = GEN_INT (const_op);
+		  op0 = XEXP (op0, 0);
+		  continue;
+		}
 	    }
 
 	  /* If we are using this shift to extract just the sign bit, we

gcc/testsuite/ChangeLog

+2010-09-13  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/45617
+	* gcc.target/i386/pr45617.c: New test.
+
 2010-09-13  Dave Korn  <dave.korn.cygwin@gmail.com>
 
 	* gcc.target/i386/volatile-2.c: Allow underscores before symbols.

gcc/testsuite/gcc.target/i386/pr45617.c

+/* PR rtl-optimization/45617 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int f1 (int x)
+{
+  return (x >> 23) > 12;
+}
+int f2 (int x)
+{
+  return x > ((13 << 23) - 1);
+}
+int f3 (int x)
+{
+  return (x >> 23) >= 12;
+}
+int f4 (int x)
+{
+  return x >= (12 << 23);
+}
+
+/* { dg-final { scan-assembler-not "sarl" } } */