ifcvt.c (cheap_bb_rtx_cost_p): Don't speculatively execute x87 instructions.

	* ifcvt.c (cheap_bb_rtx_cost_p): Don't speculatively execute
	x87 instructions.

From-SVN: r116501

gcc/ChangeLog

+2006-08-27  Roger Sayle  <roger@eyesopen.com>
+
+	* ifcvt.c (cheap_bb_rtx_cost_p): Don't speculatively execute
+	x87 instructions.
+
 2006-08-27  Kazu Hirata  <kazu@codesourcery.com>
 
 	* config/i386/crtfastmath.c: Fix a comment typo.

gcc/ifcvt.c

 /* If-conversion support.
-   Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005
+   Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2006
    Free Software Foundation, Inc.
 
    This file is part of GCC.
@@ -153,14 +153,16 @@ cheap_bb_rtx_cost_p (basic_block bb, int max_cost)
 
 	  /* If this instruction is the load or set of a "stack" register,
 	     such as a floating point register on x87, then the cost of
-	     speculatively executing this instruction needs to include
-	     the additional cost of popping this register off of the
-	     register stack.  */
+	     speculatively executing this insn may need to include
+	     the additional cost of popping its result off of the
+	     register stack.  Unfortunately, correctly recognizing and
+	     accounting for this additional overhead is tricky, so for
+	     now we simply prohibit such speculative execution.  */
 #ifdef STACK_REGS
 	  {
 	    rtx set = single_set (insn);
 	    if (set && STACK_REG_P (SET_DEST (set)))
-	      cost += COSTS_N_INSNS (1);
+	      return false;
 	  }
 #endif