combine: Fix ICE in try_combine on pr112494.c [PR112560]

The compiler, configured with --enable-checking=yes,rtl,extra ICEs with:

internal compiler error: RTL check: expected elt 0 type 'e' or 'u', have 'E' (rtx unspec) in try_combine, at combine.cc:3237

This is

3236			  /* Just replace the CC reg with a new mode.  */
3237			  SUBST (XEXP (*cc_use_loc, 0), newpat_dest);
3238			  undobuf.other_insn = cc_use_insn;

in combine.cc, where *cc_use_loc is

(unspec:DI [
        (reg:CC 17 flags)
    ] UNSPEC_PUSHFL)

combine assumes CC must be used inside of a comparison and uses XEXP (..., 0)
without checking on the RTX type of the argument.

Replace cc_use_loc with the entire new RTX only in case cc_use_loc satisfies
COMPARISON_P predicate.  Otherwise scan the entire cc_use_loc RTX for CC reg
to be updated with a new mode.

	PR rtl-optimization/112560

gcc/ChangeLog:

	* combine.cc (try_combine): Replace cc_use_loc with the entire
	new RTX only in case cc_use_loc satisfies COMPARISON_P predicate.
	Otherwise scan the entire cc_use_loc RTX for CC reg to be updated
	with a new mode.
	* config/i386/i386.md (@pushf<mode>2): Allow all CC modes for
	operand 1.

Author: ubizjak

gcc/combine.cc

@@ -3222,8 +3222,7 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
 #endif
 	      /* Cases for modifying the CC-using comparison.  */
 	      if (compare_code != orig_compare_code
-		  /* ??? Do we need to verify the zero rtx?  */
-		  && XEXP (*cc_use_loc, 1) == const0_rtx)
+		  && COMPARISON_P (*cc_use_loc))
 		{
 		  /* Replace cc_use_loc with entire new RTX.  */
 		  SUBST (*cc_use_loc,
@@ -3233,8 +3232,19 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
 		}
 	      else if (compare_mode != orig_compare_mode)
 		{
+		  subrtx_ptr_iterator::array_type array;
+
 		  /* Just replace the CC reg with a new mode.  */
-		  SUBST (XEXP (*cc_use_loc, 0), newpat_dest);
+		  FOR_EACH_SUBRTX_PTR (iter, array, cc_use_loc, NONCONST)
+		    {
+		      rtx *loc = *iter;
+		      if (REG_P (*loc)
+			  && REGNO (*loc) == REGNO (newpat_dest))
+			{
+			  SUBST (*loc, newpat_dest);
+			  iter.skip_subrtxes ();
+			}
+		    }
 		  undobuf.other_insn = cc_use_insn;
 		}
 	    }

gcc/config/i386/i386.md

@@ -2219,9 +2219,9 @@
 
 (define_insn "@pushfl<mode>2"
   [(set (match_operand:W 0 "push_operand" "=<")
-	(unspec:W [(match_operand:CC 1 "flags_reg_operand")]
+	(unspec:W [(match_operand 1 "flags_reg_operand")]
 		  UNSPEC_PUSHFL))]
-  ""
+  "GET_MODE_CLASS (GET_MODE (operands[1])) == MODE_CC"
   "pushf{<imodesuffix>}"
   [(set_attr "type" "push")
    (set_attr "mode" "<MODE>")])