2015-02-26  Jakub Jelinek  <jakub@redhat.com>
	    Aldy Hernandez  <aldyh@redhat.com>

	PR rtl-optimization/65220
	* config/i386/i386.md (*udivmod<mode>4_pow2): New.

--- gcc/config/i386/i386.md	(revision 221063)
+++ gcc/config/i386/i386.md	(revision 221064)
@@ -7331,6 +7331,32 @@ (define_insn_and_split "*udivmod<mode>4"
   [(set_attr "type" "multi")
    (set_attr "mode" "<MODE>")])
 
+;; Optimize division or modulo by constant power of 2, if the constant
+;; materializes only after expansion.
+(define_insn_and_split "*udivmod<mode>4_pow2"
+  [(set (match_operand:SWI48 0 "register_operand" "=r")
+	(udiv:SWI48 (match_operand:SWI48 2 "register_operand" "0")
+		    (match_operand:SWI48 3 "const_int_operand" "n")))
+   (set (match_operand:SWI48 1 "register_operand" "=r")
+	(umod:SWI48 (match_dup 2) (match_dup 3)))
+   (clobber (reg:CC FLAGS_REG))]
+  "UINTVAL (operands[3]) - 2 < <MODE_SIZE> * BITS_PER_UNIT
+   && (UINTVAL (operands[3]) & (UINTVAL (operands[3]) - 1)) == 0"
+  "#"
+  "&& reload_completed"
+  [(set (match_dup 1) (match_dup 2))
+   (parallel [(set (match_dup 0) (lshiftrt:<MODE> (match_dup 2) (match_dup 4)))
+	      (clobber (reg:CC FLAGS_REG))])
+   (parallel [(set (match_dup 1) (and:<MODE> (match_dup 1) (match_dup 5)))
+	      (clobber (reg:CC FLAGS_REG))])]
+{
+  int v = exact_log2 (UINTVAL (operands[3]));
+  operands[4] = GEN_INT (v);
+  operands[5] = GEN_INT ((HOST_WIDE_INT_1U << v) - 1);
+}
+  [(set_attr "type" "multi")
+   (set_attr "mode" "<MODE>")])
+
 (define_insn "*udivmod<mode>4_noext"
   [(set (match_operand:SWIM248 0 "register_operand" "=a")
 	(udiv:SWIM248 (match_operand:SWIM248 2 "register_operand" "0")
--- gcc/testsuite/gcc.target/i386/pr65520.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr65520.c	(revision 221064)
@@ -0,0 +1,20 @@
+/* PR target/65520 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int foo (void *);
+
+void
+bar (void)
+{
+  unsigned s = 128;
+  while (1)
+    {
+      unsigned b[s];
+      if (foo (b))
+	break;
+      s *= 2;
+    }
+}
+
+/* { dg-final { scan-assembler-not "div\[^\n\r]*%" } } */