Fix bogus warning with -Wlogical-not-parentheses (PR c/77292)

[Marek Polacek]

On Thu, Aug 25, 2016 at 11:17:37AM +0200, Richard Biener wrote:
> On Wed, Aug 24, 2016 at 7:43 PM, Marek Polacek <polacek@redhat.com> wrote:
> > The -Wlogical-not-parentheses deliberately doesn't warn when the RHS has
> > boolean type.  But since in C the type of a comparison is int, we need
> > to check for tcc_comparison, too.
> >
> > Bootstrapped/regtested on x86_64-linux and ppc64le-redhat-linux, ok for trunk?
> 
> What about using truth_value_p ()?  That also includes && and || (just
> in case those
> do not have boolean type).

You're right that I should also handle || and && (done in this patch).  But I
can't use truth_value_p because we want to warn for e.g. "!a == (a & b)".

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2016-08-25  Marek Polacek  <polacek@redhat.com>

	PR c/77292
	* c-common.c (warn_logical_not_parentheses): Don't warn for
	a comparison or a logical operator.

	* c-c++-common/Wlogical-not-parentheses-1.c: New test.

diff --git gcc/c-family/c-common.c gcc/c-family/c-common.c
index 3feb910..3656c57 100644
--- gcc/c-family/c-common.c
+++ gcc/c-family/c-common.c
@@ -1481,7 +1481,8 @@ warn_tautological_cmp (location_t loc, enum tree_code code, tree lhs, tree rhs)
 
 /* Warn about logical not used on the left hand side operand of a comparison.
    This function assumes that the LHS is inside of TRUTH_NOT_EXPR.
-   Do not warn if RHS is of a boolean type.  */
+   Do not warn if RHS is of a boolean type, a logical operator, or
+   a comparison.  */
 
 void
 warn_logical_not_parentheses (location_t location, enum tree_code code,
@@ -1489,7 +1490,10 @@ warn_logical_not_parentheses (location_t location, enum tree_code code,
 {
   if (TREE_CODE_CLASS (code) != tcc_comparison
       || TREE_TYPE (rhs) == NULL_TREE
-      || TREE_CODE (TREE_TYPE (rhs)) == BOOLEAN_TYPE)
+      || TREE_CODE (TREE_TYPE (rhs)) == BOOLEAN_TYPE
+      || COMPARISON_CLASS_P (rhs)
+      || TREE_CODE (rhs) == TRUTH_ANDIF_EXPR
+      || TREE_CODE (rhs) == TRUTH_ORIF_EXPR)
     return;
 
   /* Don't warn for !x == 0 or !y != 0, those are equivalent to
diff --git gcc/testsuite/c-c++-common/Wlogical-not-parentheses-1.c gcc/testsuite/c-c++-common/Wlogical-not-parentheses-1.c
index e69de29..ba57437 100644
--- gcc/testsuite/c-c++-common/Wlogical-not-parentheses-1.c
+++ gcc/testsuite/c-c++-common/Wlogical-not-parentheses-1.c
@@ -0,0 +1,25 @@
+/* PR c/77292 */
+/* { dg-do compile } */
+/* { dg-options "-Wlogical-not-parentheses" } */
+
+ /* Test that we don't warn if rhs is a comparison or a logical op.  */
+
+int
+foo (int a, int b)
+{
+  int r = 0;
+  r += !a == (a < b);
+  r += !a == (a > b);
+  r += !a == (a >= b);
+  r += !a == (a <= b);
+  r += !a == (a != b);
+  r += !a == (a == b);
+  r += !a == (a || b);
+  r += !a == (a && b);
+  r += !a == (!b);
+
+  r += !a == (a ^ b); /* { dg-warning "logical not is only applied to the left hand side of comparison" } */
+  r += !a == (a | b); /* { dg-warning "logical not is only applied to the left hand side of comparison" } */
+  r += !a == (a & b); /* { dg-warning "logical not is only applied to the left hand side of comparison" } */
+  return r;
+}

	Marek