This improves -Wbool-compare a bit: boolean >= 0 is always true, on the other
hand boolean < 0 is always false, and similar.
One feature/bug is that in C++ we don't warn for e.g. bool >= false, since the
warning cares about <bool> CMP <non-bool> or <non-bool> CMP <bool>. I can fix
that in a follow-up if anyone wants me to.
Bootstrapped (-> GCC itself is clean)/regtested on x86_64-linux, ok for trunk?
2015-04-28 Marek Polacek <pola...@redhat.com>
PR c/64610
* c-common.c (maybe_warn_bool_compare): Warn when comparing a boolean
with 0/1.
* c-c++-common/Wbool-compare-1.c (fn1): Remove a few lines.
* c-c++-common/Wbool-compare-2.c: New test.
diff --git gcc/c-family/c-common.c gcc/c-family/c-common.c
index 9797e17..afd6edf2 100644
--- gcc/c-family/c-common.c
+++ gcc/c-family/c-common.c
@@ -11906,8 +11906,8 @@ maybe_warn_bool_compare (location_t loc, enum tree_code
code, tree op0,
if (!integer_zerop (cst) && !integer_onep (cst))
{
- int sign = (TREE_CODE (op0) == INTEGER_CST)
- ? tree_int_cst_sgn (cst) : -tree_int_cst_sgn (cst);
+ int sign = (TREE_CODE (op0) == INTEGER_CST
+ ? tree_int_cst_sgn (cst) : -tree_int_cst_sgn (cst));
if (code == EQ_EXPR
|| ((code == GT_EXPR || code == GE_EXPR) && sign < 0)
|| ((code == LT_EXPR || code == LE_EXPR) && sign > 0))
@@ -11917,6 +11917,18 @@ maybe_warn_bool_compare (location_t loc, enum
tree_code code, tree op0,
warning_at (loc, OPT_Wbool_compare, "comparison of constant %qE "
"with boolean expression is always true", cst);
}
+ else if (integer_zerop (cst) || integer_onep (cst))
+ {
+ /* Do some magic to get the right diagnostics. */
+ bool flag = TREE_CODE (op0) == INTEGER_CST;
+ flag = integer_zerop (cst) ? flag : !flag;
+ if ((code == GE_EXPR && !flag) || (code == LE_EXPR && flag))
+ warning_at (loc, OPT_Wbool_compare, "comparison of constant %qE "
+ "with boolean expression is always true", cst);
+ else if ((code == LT_EXPR && !flag) || (code == GT_EXPR && flag))
+ warning_at (loc, OPT_Wbool_compare, "comparison of constant %qE "
+ "with boolean expression is always false", cst);
+ }
}
/* The C and C++ parsers both use vectors to hold function arguments.
diff --git gcc/testsuite/c-c++-common/Wbool-compare-1.c
gcc/testsuite/c-c++-common/Wbool-compare-1.c
index 5b03e06..2f435f6 100644
--- gcc/testsuite/c-c++-common/Wbool-compare-1.c
+++ gcc/testsuite/c-c++-common/Wbool-compare-1.c
@@ -72,15 +72,10 @@ fn1 (bool b)
r = b == true;
r = b != true;
- /* Some of these don't make much sense, but we don't warn. */
- r = b < false;
- r = b >= false;
r = b <= false;
r = b > false;
r = b < true;
r = b >= true;
- r = b <= true;
- r = b > true;
}
void
diff --git gcc/testsuite/c-c++-common/Wbool-compare-2.c
gcc/testsuite/c-c++-common/Wbool-compare-2.c
index e69de29..6330322 100644
--- gcc/testsuite/c-c++-common/Wbool-compare-2.c
+++ gcc/testsuite/c-c++-common/Wbool-compare-2.c
@@ -0,0 +1,100 @@
+/* PR c/64610 */
+/* { dg-do compile } */
+/* { dg-options "-Wbool-compare" } */
+
+#ifndef __cplusplus
+# define bool _Bool
+# define true 1
+# define false 0
+#endif
+
+extern bool foo (void);
+
+enum { A, B };
+
+int
+fn1 (bool b)
+{
+ int r = 0;
+
+ r += b >= 0; /* { dg-warning "with boolean expression is always true" } */
+ r += b > 0;
+ r += b < 0; /* { dg-warning "with boolean expression is always false" } */
+ r += b <= 0;
+
+ r += b >= 1;
+ r += b > 1; /* { dg-warning "with boolean expression is always false" } */
+ r += b < 1;
+ r += b <= 1; /* { dg-warning "with boolean expression is always true" } */
+
+ r += foo () >= 0; /* { dg-warning "with boolean expression is always true" }
*/
+ r += foo () > 0;
+ r += foo () < 0; /* { dg-warning "with boolean expression is always false" }
*/
+ r += foo () <= 0;
+
+ r += foo () >= 1;
+ r += foo () > 1; /* { dg-warning "with boolean expression is always false" }
*/
+ r += foo () < 1;
+ r += foo () <= 1; /* { dg-warning "with boolean expression is always true" }
*/
+
+ r += b >= A; /* { dg-warning "with boolean expression is always true" } */
+ r += b > A;
+ r += b < A; /* { dg-warning "with boolean expression is always false" } */
+ r += b <= A;
+
+ r += b >= B;
+ r += b > B; /* { dg-warning "with boolean expression is always false" } */
+ r += b < B;
+ r += b <= B; /* { dg-warning "with boolean expression is always true" } */
+
+ /* Swap LHS and RHS. */
+ r += 0 >= b;
+ r += 0 > b; /* { dg-warning "with boolean expression is always false" } */
+ r += 0 < b;
+ r += 0 <= b; /* { dg-warning "with boolean expression is always true" } */
+
+ r += 1 >= b; /* { dg-warning "with boolean expression is always true" } */
+ r += 1 > b;
+ r += 1 < b; /* { dg-warning "with boolean expression is always false" } */
+ r += 1 <= b;
+
+ r += 0 >= foo ();
+ r += 0 > foo (); /* { dg-warning "with boolean expression is always false" }
*/
+ r += 0 < foo ();
+ r += 0 <= foo (); /* { dg-warning "with boolean expression is always true" }
*/
+
+ r += 1 >= foo (); /* { dg-warning "with boolean expression is always true" }
*/
+ r += 1 > foo ();
+ r += 1 < foo (); /* { dg-warning "with boolean expression is always false" }
*/
+ r += 1 <= foo ();
+
+ r += A >= b;
+ r += A > b; /* { dg-warning "with boolean expression is always false" } */
+ r += A < b;
+ r += A <= b; /* { dg-warning "with boolean expression is always true" } */
+
+ r += B >= b; /* { dg-warning "with boolean expression is always true" } */
+ r += B > b;
+ r += B < b; /* { dg-warning "with boolean expression is always false" } */
+ r += B <= b;
+
+ return r;
+}
+
+int
+fn2 (int i, int j)
+{
+ int r = 0;
+
+ r += (i == j) >= 0; /* { dg-warning "with boolean expression is always true"
} */
+ r += (i == j) > 0;
+ r += (i == j) < 0; /* { dg-warning "with boolean expression is always false"
} */
+ r += (i == j) <= 0;
+
+ r += (i == j) >= 1;
+ r += (i == j) > 1; /* { dg-warning "with boolean expression is always false"
} */
+ r += (i == j) < 1;
+ r += (i == j) <= 1; /* { dg-warning "with boolean expression is always true"
} */
+
+ return r;
+}
Marek
