[C++ PATCH] Avoid code generation changes with -Wnonnull-compare vs. -Wno-nonnull-compare (PR c++/86569)

[Richard Biener]

On July 22, 2018 9:15:50 PM GMT+02:00, Jakub Jelinek <jakub@redhat.com> wrote:
>Hi!
>
>A couple of -fcompare-debug=-Wsomething PRs have been filed recently,
>this
>fixes one of them.  Changing code generation based on TREE_NO_WARNING
>flag
>which usually gets set only in the warning code, or on warn_* option is
>undesirable.  This patch prevents that kind of folding regardless of
>the
>warning options, the GIMPLE optimizers can handle it fine (but it makes
>a
>difference with -O0).
>
>Bootstrapped/regtested on x86_64-linux (only, i686-linux bootstrap is
>broken), ok for trunk?

OK. 

Richard. 

>2018-07-22  Jakub Jelinek  <jakub@redhat.com>
>
>	PR c++/86569
>	* cp-gimplify.c (cp_fold): Don't fold comparisons into other kind
>	of expressions other than INTEGER_CST regardless of TREE_NO_WARNING
>	or warn_nonnull_compare.
>
>	* g++.dg/warn/Wnonnull-compare-9.C: New test.
>
>--- gcc/cp/cp-gimplify.c.jj	2018-07-16 09:43:03.237023048 +0200
>+++ gcc/cp/cp-gimplify.c	2018-07-19 11:44:24.881759294 +0200
>@@ -2381,21 +2381,26 @@ cp_fold (tree x)
>       else
> 	x = fold (x);
> 
>-      if (TREE_NO_WARNING (org_x)
>-	  && warn_nonnull_compare
>-	  && COMPARISON_CLASS_P (org_x))
>+      /* This is only needed for -Wnonnull-compare and only if
>+	 TREE_NO_WARNING (org_x), but to avoid that option affecting code
>+	 generation, we do it always.  */
>+      if (COMPARISON_CLASS_P (org_x))
> 	{
> 	  if (x == error_mark_node || TREE_CODE (x) == INTEGER_CST)
> 	    ;
> 	  else if (COMPARISON_CLASS_P (x))
>-	    TREE_NO_WARNING (x) = 1;
>+	    {
>+	      if (TREE_NO_WARNING (org_x) && warn_nonnull_compare)
>+		TREE_NO_WARNING (x) = 1;
>+	    }
> 	  /* Otherwise give up on optimizing these, let GIMPLE folders
> 	     optimize those later on.  */
> 	  else if (op0 != TREE_OPERAND (org_x, 0)
> 		   || op1 != TREE_OPERAND (org_x, 1))
> 	    {
> 	      x = build2_loc (loc, code, TREE_TYPE (org_x), op0, op1);
>-	      TREE_NO_WARNING (x) = 1;
>+	      if (TREE_NO_WARNING (org_x) && warn_nonnull_compare)
>+		TREE_NO_WARNING (x) = 1;
> 	    }
> 	  else
> 	    x = org_x;
>--- gcc/testsuite/g++.dg/warn/Wnonnull-compare-9.C.jj	2018-07-19
>11:57:41.909727597 +0200
>+++ gcc/testsuite/g++.dg/warn/Wnonnull-compare-9.C	2018-07-19
>11:57:14.627696497 +0200
>@@ -0,0 +1,11 @@
>+// PR c++/86569
>+// { dg-do compile }
>+// { dg-options "-fcompare-debug=-Wnonnull-compare" }
>+
>+bool b;
>+
>+int
>+main ()
>+{
>+  return ((!b) != 0);
>+}
>
>	Jakub