From 0000ea4fb4eaacbd2c954d78d7f8e9f03c7be739 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Tue, 10 Nov 2020 15:56:20 +0100
Subject: [PATCH] c, c++: Fix up -Wunused-value on COMPLEX_EXPRs [PR97748]
The -Wunused-value warning in both C and C++ FEs (implemented
significantly differently between the two) sees the COMPLEX_EXPRs created
e.g. for complex pre/post increment and many other expressions as useless
and warns about it.
For the C warning implementation, on e.g.
COMPLEX_EXPR < ++REALPART_EXPR <x>, IMAGPART_EXPR <x>>;
would warn even on the IMAGPART_EXPR <x> there alone etc., so what works
is check if we'd warn about both operands of COMPLEX_EXPR and if yes,
warn on the whole COMPLEX_EXPR, otherwise don't warn.
The C++ warning implementation is significantly different and for that one
the only warn if both would be warned about doesn't really work,
we then miss warnings e.g. about
COMPLEX_EXPR <REALPART_EXPR <SAVE_EXPR <x>> + 1.0e+0, IMAGPART_EXPR <SAVE_EXPR <x>>> >>>>>
The patch replaces the warning_at call with call to the c-family
warn_if_unused_value function.
On the testcase which after the initial new tests contains pretty much
everything from gcc.dg/Wunused-value-1.c both approaches seem to work
nicely.
2020-11-10 Jakub Jelinek <jakub@redhat.com>
PR c/97748
gcc/c-family/
* c-common.h (warn_if_unused_value): Add quiet argument defaulted
to false.
* c-warn.c (warn_if_unused_value): Likewise. Pass it down
recursively and just return true instead of warning if it is true.
Handle COMPLEX_EXPR.
gcc/cp/
* cvt.c (convert_to_void): Check (complain & tf_warning) in the outer
if rather than twice times in the inner one. Use warn_if_unused_value.
Formatting fix.
gcc/testsuite/
* c-c++-common/Wunused-value-1.c: New test.
---
gcc/c-family/c-common.h | 2 +-
gcc/c-family/c-warn.c | 13 +++++--
gcc/cp/cvt.c | 38 ++++++++------------
gcc/testsuite/c-c++-common/Wunused-value-1.c | 33 +++++++++++++++++
4 files changed, 59 insertions(+), 27 deletions(-)
create mode 100644 gcc/testsuite/c-c++-common/Wunused-value-1.c
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index b80db230a6df..94f4868915a2 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1365,7 +1365,7 @@ extern void warn_tautological_cmp (const op_location_t &, enum tree_code,
tree, tree);
extern void warn_logical_not_parentheses (location_t, enum tree_code, tree,
tree);
-extern bool warn_if_unused_value (const_tree, location_t);
+extern bool warn_if_unused_value (const_tree, location_t, bool = false);
extern bool strict_aliasing_warning (location_t, tree, tree);
extern void sizeof_pointer_memaccess_warning (location_t *, tree,
vec<tree, va_gc> *, tree *,
diff --git a/gcc/c-family/c-warn.c b/gcc/c-family/c-warn.c
index 68b093e0d467..6d1f9a73e448 100644
--- a/gcc/c-family/c-warn.c
+++ b/gcc/c-family/c-warn.c
@@ -585,7 +585,7 @@ warn_logical_not_parentheses (location_t location, enum tree_code code,
(potential) location of the expression. */
bool
-warn_if_unused_value (const_tree exp, location_t locus)
+warn_if_unused_value (const_tree exp, location_t locus, bool quiet)
{
restart:
if (TREE_USED (exp) || TREE_NO_WARNING (exp))
@@ -633,7 +633,7 @@ warn_if_unused_value (const_tree exp, location_t locus)
goto restart;
case COMPOUND_EXPR:
- if (warn_if_unused_value (TREE_OPERAND (exp, 0), locus))
+ if (warn_if_unused_value (TREE_OPERAND (exp, 0), locus, quiet))
return true;
/* Let people do `(foo (), 0)' without a warning. */
if (TREE_CONSTANT (TREE_OPERAND (exp, 1)))
@@ -648,6 +648,13 @@ warn_if_unused_value (const_tree exp, location_t locus)
return false;
goto warn;
+ case COMPLEX_EXPR:
+ /* Warn only if both operands are unused. */
+ if (warn_if_unused_value (TREE_OPERAND (exp, 0), locus, true)
+ && warn_if_unused_value (TREE_OPERAND (exp, 1), locus, true))
+ goto warn;
+ return false;
+
case INDIRECT_REF:
/* Don't warn about automatic dereferencing of references, since
the user cannot control it. */
@@ -671,6 +678,8 @@ warn_if_unused_value (const_tree exp, location_t locus)
return false;
warn:
+ if (quiet)
+ return true;
return warning_at (locus, OPT_Wunused_value, "value computed is not used");
}
}
diff --git a/gcc/cp/cvt.c b/gcc/cp/cvt.c
index c9e7b1ff0441..bcd7c5af81c2 100644
--- a/gcc/cp/cvt.c
+++ b/gcc/cp/cvt.c
@@ -1568,12 +1568,13 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain)
&& warn_unused_value
&& !TREE_NO_WARNING (expr)
&& !processing_template_decl
- && !cp_unevaluated_operand)
+ && !cp_unevaluated_operand
+ && (complain & tf_warning))
{
/* The middle end does not warn about expressions that have
been explicitly cast to void, so we must do so here. */
- if (!TREE_SIDE_EFFECTS (expr)) {
- if (complain & tf_warning)
+ if (!TREE_SIDE_EFFECTS (expr))
+ {
switch (implicit)
{
case ICV_SECOND_OF_COND:
@@ -1605,14 +1606,10 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain)
default:
gcc_unreachable ();
}
- }
+ }
else
{
- tree e;
- enum tree_code code;
- enum tree_code_class tclass;
-
- e = expr;
+ tree e = expr;
/* We might like to warn about (say) "(int) f()", as the
cast has no effect, but the compiler itself will
generate implicit conversions under some
@@ -1626,21 +1623,14 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain)
while (TREE_CODE (e) == NOP_EXPR)
e = TREE_OPERAND (e, 0);
- code = TREE_CODE (e);
- tclass = TREE_CODE_CLASS (code);
- if ((tclass == tcc_comparison
- || tclass == tcc_unary
- || (tclass == tcc_binary
- && !(code == MODIFY_EXPR
- || code == INIT_EXPR
- || code == PREDECREMENT_EXPR
- || code == PREINCREMENT_EXPR
- || code == POSTDECREMENT_EXPR
- || code == POSTINCREMENT_EXPR))
- || code == VEC_PERM_EXPR
- || code == VEC_COND_EXPR)
- && (complain & tf_warning))
- warning_at (loc, OPT_Wunused_value, "value computed is not used");
+ enum tree_code code = TREE_CODE (e);
+ enum tree_code_class tclass = TREE_CODE_CLASS (code);
+ if (tclass == tcc_comparison
+ || tclass == tcc_unary
+ || tclass == tcc_binary
+ || code == VEC_PERM_EXPR
+ || code == VEC_COND_EXPR)
+ warn_if_unused_value (e, loc);
}
}
expr = build1 (CONVERT_EXPR, void_type_node, expr);
diff --git a/gcc/testsuite/c-c++-common/Wunused-value-1.c b/gcc/testsuite/c-c++-common/Wunused-value-1.c
new file mode 100644
index 000000000000..90c9d93340f2
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wunused-value-1.c
@@ -0,0 +1,33 @@
+/* PR c/97748 */
+/* { dg-do compile } */
+/* { dg-options "-Wunused-value" } */
+
+double _Complex f ();
+double _Complex *p;
+
+double _Complex
+foo (double _Complex x)
+{
+ ++x; /* { dg-bogus "value computed is not used" } */
+ --x; /* { dg-bogus "value computed is not used" } */
+ x += 1; /* { dg-bogus "value computed is not used" } */
+ x += 1.0iF; /* { dg-bogus "value computed is not used" } */
+ x++; /* { dg-bogus "value computed is not used" } */
+ x--; /* { dg-bogus "value computed is not used" } */
+ x + 1; /* { dg-warning "value computed is not used" } */
+ (void) (x + 1); /* { dg-bogus "value computed is not used" } */
+ 1 + f (); /* { dg-warning "value computed is not used" } */
+ f () + f (); /* { dg-warning "value computed is not used" } */
+ f () + f (), f (); /* { dg-warning "value computed is not used" } */
+ f ();
+ (void) f ();
+ *p++; /* { dg-warning "value computed is not used" } */
+ ++*p; /* { dg-bogus "value computed is not used" } */
+ (*p ? f () : 0);
+ ({ f (); });
+ ({ f () + 1; });
+ ({ f (); 0; });
+ ({ f () + 1; 0; }); /* { dg-warning "value computed is not used" } */
+ 1 + ({ f (); }); /* { dg-warning "value computed is not used" } */
+ return x;
+}
--
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