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

[Uros Bizjak]

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.

Skip the modification of CC-using operation if *cc_use_loc is not COMPARISON_P.

    PR middle-end/112560

gcc/ChangeLog:

    * combine.cc (try_combine): Skip the modification of CC-using
    operation if *cc_use_loc is not COMPARISON_P.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

OK for master?

Uros.
-------------- next part --------------
diff --git a/gcc/combine.cc b/gcc/combine.cc
index 6344cd3c9f2..a270138b59f 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -3184,11 +3184,16 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
 	  && (cc_use_loc = find_single_use (SET_DEST (newpat), i3,
 					    &cc_use_insn)))
 	{
-	  compare_code = orig_compare_code = GET_CODE (*cc_use_loc);
-	  if (is_a <scalar_int_mode> (GET_MODE (i2dest), &mode))
-	    compare_code = simplify_compare_const (compare_code, mode,
-						   &op0, &op1);
-	  target_canonicalize_comparison (&compare_code, &op0, &op1, 1);
+	  if (COMPARISON_P (*cc_use_loc))
+	    {
+	      compare_code = orig_compare_code = GET_CODE (*cc_use_loc);
+	      if (is_a <scalar_int_mode> (GET_MODE (i2dest), &mode))
+		compare_code = simplify_compare_const (compare_code, mode,
+						       &op0, &op1);
+	      target_canonicalize_comparison (&compare_code, &op0, &op1, 1);
+	    }
+	  else
+	    cc_use_loc = NULL;
 	}
 
       /* Do the rest only if op1 is const0_rtx, which may be the