[backport from gcc-4.7/trunk, fixes MIPS gcc-loops bug PR50380 <mikpe@it.uu.se>]

gcc/

2011-12-19  Sandra Loosemore  <sandra@codesourcery.com>
	    Tom de Vries <tom@codesourcery.com>

	PR rtl-opt/50380
	* cse.c (find_comparison_args): Detect fixed point and
	bail early.

gcc/testsuite/

2011-12-19  Sandra Loosemore  <sandra@codesourcery.com>
	    Tom de Vries <tom@codesourcery.com>

	PR rtl-opt/50380
	* gcc.c-torture/compile/pr50380.c: New testcase.

--- gcc-4.6.2/gcc/cse.c.~1~	2011-06-14 17:01:10.000000000 +0200
+++ gcc-4.6.2/gcc/cse.c	2011-12-24 16:08:54.000000000 +0100
@@ -3054,6 +3054,12 @@ find_comparison_args (enum rtx_code code
 	  if (! exp_equiv_p (p->exp, p->exp, 1, false))
 	    continue;
 
+	  /* If it's the same comparison we're already looking at, skip it.  */
+	  if (COMPARISON_P (p->exp)
+	      && XEXP (p->exp, 0) == arg1
+	      && XEXP (p->exp, 1) == arg2)
+	    continue;
+
 	  if (GET_CODE (p->exp) == COMPARE
 	      /* Another possibility is that this machine has a compare insn
 		 that includes the comparison code.  In that case, ARG1 would
--- gcc-4.6.2/gcc/testsuite/gcc.c-torture/compile/pr50380.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.6.2/gcc/testsuite/gcc.c-torture/compile/pr50380.c	2011-12-24 16:08:54.000000000 +0100
@@ -0,0 +1,12 @@
+/* This test used to get stuck in an infinite loop in find_comparison_args
+   when compiling for MIPS at -O2.  */
+
+__attribute__ ((__noreturn__)) extern void fail (void);
+
+char x;
+
+void foo (const unsigned char y)
+{
+   ((void) (__builtin_expect((!! y == y), 1) ? 0 : (fail (), 0)));
+   x = ! y;
+}