On Wed, Jan 22, 2014 at 12:15:00AM +0100, Jakub Jelinek wrote:
> And for
> (bar (), (bar (), (bar (), (bar (), (bar (), (bar (), (bar (), 7)))))));
> ?
Argh, for this one we've got COMPOUND_EXPRs even in TREE_OPERAND (r, 1).
Fixed & sorry.
> On the other side, there is warn_if_unused_value, which specifically has:
> /* Let people do `(foo (), 0)' without a warning. */
> if (TREE_CONSTANT (TREE_OPERAND (exp, 1)))
> return false;
> so perhaps it is intentional that we don't warn about this?
> That stuff dates all the way back to r759. Though I wonder why it would
> be desirable to warn about this for C++ and not for C.
This is confusing. I'll try to sumarize what I see. Let A, B, C, D
be stmts:
A: bar (), 1;
B: (bar (), 1);
C: bar (), 5 * i;
D: (bar (), 5 * i);
C++ warns on A and C ("right operand..."), those parentheses suppress warnings.
C before patch warns on C and D with "value computed is not used".
C with my patch warns on A, B, C, and D with "right-hand operand...".
I think what my patch does should be desirable. I added a few more
tests into the testcase.
2014-01-22 Marek Polacek <pola...@redhat.com>
PR c/59871
c/
* c-typeck.c (build_compound_expr): Warn even for right-hand operand
of a comma expression.
(emit_side_effect_warnings): Likewise.
libdecnumber/
* decNumberLocal.h (UBFROMUS, UBFROMUI): Remove last argument.
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 22:04:34.331223218 +0100
@@ -153,10 +153,9 @@ see the files COPYING3 and COPYING.RUNTI
#define UBTOUI(b) (memcpy((void *)&uiwork, b, 4), uiwork)
/* 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)
+ /* Has to use uiwork because i may be an expression. */
+ #define UBFROMUS(b, i) (uswork=(i), memcpy(b, (void *)&uswork, 2))
+ #define UBFROMUI(b, i) (uiwork=(i), memcpy(b, (void *)&uiwork, 4))
/* 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 2014-01-22 11:04:51.681894533 +0100
@@ -4776,6 +4776,23 @@ build_compound_expr (location_t loc, tre
"left-hand operand of comma expression has no effect");
}
}
+ else if (TREE_CODE (expr1) == COMPOUND_EXPR
+ && warn_unused_value)
+ {
+ tree r = expr1;
+ location_t cloc = loc;
+ while (TREE_CODE (r) == COMPOUND_EXPR)
+ {
+ if (EXPR_HAS_LOCATION (r))
+ cloc = EXPR_LOCATION (r);
+ r = TREE_OPERAND (r, 1);
+ }
+ if (!TREE_SIDE_EFFECTS (r)
+ && !VOID_TYPE_P (TREE_TYPE (r))
+ && !CONVERT_EXPR_P (r))
+ warning_at (cloc, OPT_Wunused_value,
+ "right-hand operand of comma expression has no effect");
+ }
/* With -Wunused, we should also warn if the left-hand operand does have
side-effects, but computes a value which is not used. For example, in
@@ -9641,6 +9658,23 @@ 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;
+ location_t cloc = loc;
+ while (TREE_CODE (r) == COMPOUND_EXPR)
+ {
+ if (EXPR_HAS_LOCATION (r))
+ cloc = EXPR_LOCATION (r);
+ 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 (cloc, 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 23:13:23.758405040
+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-hand operand of comma expression
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 2014-01-22 11:00:54.669889124 +0100
@@ -0,0 +1,22 @@
+/* PR c/59871 */
+/* { dg-do compile } */
+/* { dg-options "-Wunused" } */
+
+extern int bar ();
+
+void
+foo (int *p, int i)
+{
+ 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" } */
+ (bar (), 1); /* { dg-warning "right-hand operand of comma expression has no
effect" } */
+ bar (), 5 * i; /* { dg-warning "right-hand operand of comma expression has
no effect" } */
+ (bar (), 5 * i); /* { dg-warning "right-hand operand of comma expression has
no effect" } */
+ (bar (), (bar (), (bar (), (bar (), (bar (), (bar (), (bar (), 7))))))); /*
{ dg-warning "right-hand operand of comma expression has no effect" } */
+ bar (), (bar (), (bar (), (bar (), (bar (), (bar (), (bar (), 7)))))); /* {
dg-warning "right-hand operand of comma expression has no effect" } */
+ bar (), (bar (), (bar (), (bar (), (bar (), (bar (), (7, bar ())))))); /* {
dg-warning "left-hand operand of comma expression has no effect" } */
+ (bar (), (bar (), (bar (), (bar (), (bar (), (bar (), (7, bar ()))))))); /*
{ dg-warning "left-hand operand of comma expression has no effect" } */
+}
Marek
