In this PR the problem was that the C FE, unlike the C++ FE, didn't
warn on e.g. bar (), 1;, that the RHS has no effect. This patch tries
to tweak the C FE so that it follows what the C++ FE does. Note that
the C++ FE uses quite imprecise locus info; the C FE's info is better.
I had to slightly adjust one testcase and a header in libdecnumber.
Regtested/bootstrapped on x86_64-linux, ok for trunk?
2014-01-21 Marek Polacek <pola...@redhat.com>
PR c/59871
c/
* c-typeck.c (build_compound_expr): Warn even for right-hand operand
of comma expression.
(emit_side_effect_warnings): Likewise.
libdecnumber/
* decNumberLocal.h (UBFROMUS, UBFROMUI): Cast last argument to void.
testsuite/
* gcc.dg/20020220-2.c: Adjust dg-warning message.
* gcc.dg/pr59871.c: New test.
--- gcc/libdecnumber/decNumberLocal.h.mp 2014-01-21 18:34:32.235540589
+0100
+++ gcc/libdecnumber/decNumberLocal.h 2014-01-21 19:04:12.173243034 +0100
@@ -155,8 +155,10 @@ see the files COPYING3 and COPYING.RUNTI
/* Store a uInt, etc., into bytes starting at a char* or uByte*. */
/* Returns i, evaluated, for convenience; has to use uiwork because */
/* i may be an expression. */
- #define UBFROMUS(b, i) (uswork=(i), memcpy(b, (void *)&uswork, 2), uswork)
- #define UBFROMUI(b, i) (uiwork=(i), memcpy(b, (void *)&uiwork, 4), uiwork)
+ #define UBFROMUS(b, i) (uswork=(i), memcpy(b, (void *)&uswork, 2), \
+ (void)uswork)
+ #define UBFROMUI(b, i) (uiwork=(i), memcpy(b, (void *)&uiwork, 4), \
+ (void)uiwork)
/* X10 and X100 -- multiply integer i by 10 or 100 */
/* [shifts are usually faster than multiply; could be conditional] */
--- gcc/gcc/c/c-typeck.c.mp 2014-01-21 11:59:33.221215248 +0100
+++ gcc/gcc/c/c-typeck.c 2014-01-21 18:10:53.900279750 +0100
@@ -4757,6 +4757,18 @@ build_compound_expr (location_t loc, tre
expr2 = TREE_OPERAND (expr2, 0);
}
+ if (TREE_CODE (expr1) == COMPOUND_EXPR
+ && warn_unused_value)
+ {
+ tree r = expr1;
+ while (TREE_CODE (r) == COMPOUND_EXPR)
+ r = TREE_OPERAND (r, 1);
+ if (!TREE_SIDE_EFFECTS (r)
+ && !VOID_TYPE_P (TREE_TYPE (r))
+ && !CONVERT_EXPR_P (r))
+ warning_at (loc, OPT_Wunused_value,
+ "right-hand operand of comma expression has no effect");
+ }
if (!TREE_SIDE_EFFECTS (expr1))
{
/* The left-hand operand of a comma expression is like an expression
@@ -9641,6 +9653,18 @@ emit_side_effect_warnings (location_t lo
if (!VOID_TYPE_P (TREE_TYPE (expr)) && !TREE_NO_WARNING (expr))
warning_at (loc, OPT_Wunused_value, "statement with no effect");
}
+ else if (TREE_CODE (expr) == COMPOUND_EXPR)
+ {
+ tree r = expr;
+ while (TREE_CODE (r) == COMPOUND_EXPR)
+ r = TREE_OPERAND (r, 1);
+ if (!TREE_SIDE_EFFECTS (r)
+ && !VOID_TYPE_P (TREE_TYPE (r))
+ && !CONVERT_EXPR_P (r)
+ && !TREE_NO_WARNING (expr))
+ warning_at (EXPR_LOC_OR_LOC (expr, loc), OPT_Wunused_value,
+ "right-hand operand of comma expression has no effect");
+ }
else
warn_if_unused_value (expr, loc);
}
--- gcc/gcc/testsuite/gcc.dg/20020220-2.c.mp 2014-01-21 14:47:58.888754509
+0100
+++ gcc/gcc/testsuite/gcc.dg/20020220-2.c 2014-01-21 15:04:53.700441224
+0100
@@ -1,5 +1,5 @@
/* PR c/4697
- Test whether value computed not used warning is given for compound
+ Test whether operand has no effect warning is given for compound
expression. */
/* { dg-do compile } */
/* { dg-options "-O2 -Wunused" } */
@@ -7,6 +7,6 @@
int b;
int foo (int a)
{
- a = a + 1, 5 * b; /* { dg-warning "value computed is not used" } */
+ a = a + 1, 5 * b; /* { dg-warning "right operand of comma operator has no
effect" } */
return a;
}
--- gcc/gcc/testsuite/gcc.dg/pr59871.c.mp 2014-01-21 16:17:49.000000000
+0100
+++ gcc/gcc/testsuite/gcc.dg/pr59871.c 2014-01-21 16:13:39.000000000 +0100
@@ -0,0 +1,15 @@
+/* PR c/59871 */
+/* { dg-do compile } */
+/* { dg-options "-Wunused" } */
+
+extern int bar ();
+
+void
+foo (int *p)
+{
+ p[0] = (bar (), 1, bar ()); /* { dg-warning "right-hand operand of comma
expression has no effect" } */
+ p[1] = (1, bar ()); /* { dg-warning "left-hand operand of comma expression
has no effect" } */
+ bar (), 1, bar (); /* { dg-warning "right-hand operand of comma expression
has no effect" } */
+ bar (), 1; /* { dg-warning "right-hand operand of comma expression has no
effect" } */
+ 1, bar (); /* { dg-warning "left-hand operand of comma expression has no
effect" } */
+}
Marek
