[PATCH v2] 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.

Undo the combination if *cc_use_loc is not COMPARISON_P.

Also remove buggy and now redundant check for (const 0) RTX as part of
the comparison.

    PR rtl-optimization/112560

gcc/ChangeLog:

    * combine.cc (try_combine): Reject the combination
    if *cc_use_loc is not COMPARISON_P.

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

OK for trunk?

Uros.
-------------- next part --------------
diff --git a/gcc/combine.cc b/gcc/combine.cc
index a4479f8d836..6dac9ffca85 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -3184,11 +3184,21 @@ 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
+	    {
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		fprintf (dump_file, "CC register not used in comparison.\n");
+	      undo_all ();
+	      return 0;
+	    }
 	}
 
       /* Do the rest only if op1 is const0_rtx, which may be the
@@ -3221,9 +3231,7 @@ 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)
+	      if (compare_code != orig_compare_code)
 		{
 		  /* Replace cc_use_loc with entire new RTX.  */
 		  SUBST (*cc_use_loc,