[PATCH] Be yet more clever about -Wunused-value in macros
Matt Beaumont-Gay
matthewbg at google.com
Wed Feb 6 14:43:46 PST 2013
Hi rsmith,
My last patch for -Wunused-value and macros broke some no-compile tests. For instance, from gtest:
#define RUN_ALL_TESTS() \
(::testing::UnitTest::GetInstance()->Run())
The Run() method here is declared with __attribute__((warn_unused_result)), and there's a test which asserts that this doesn't compile (with -Werror):
void f() {
RUN_ALL_TESTS();
}
This patch carves out an exception from the "don't warn about unused values in macro bodies" rule: if the entirety of the macro (mod parentheses) is a call expression, we potentially should warn.
http://llvm-reviews.chandlerc.com/D380
Files:
lib/Sema/SemaStmt.cpp
test/Sema/unused-expr.c
Index: lib/Sema/SemaStmt.cpp
===================================================================
--- lib/Sema/SemaStmt.cpp
+++ lib/Sema/SemaStmt.cpp
@@ -158,8 +158,21 @@
if (!E)
return;
SourceLocation ExprLoc = E->IgnoreParens()->getExprLoc();
- if (SourceMgr.isInSystemMacro(ExprLoc) ||
- SourceMgr.isMacroBodyExpansion(ExprLoc))
+ if (SourceMgr.isInSystemMacro(ExprLoc))
+ return;
+ // In general, we don't want to warn about unused values coming from
+ // expressions written in macro bodies. However, we do carve out an exception:
+ // if the expression is a CallExpr, and it is the entire body of the macro
+ // (mod parentheses), the macro isn't doing anything clever and we should
+ // still potentially warn.
+ if (SourceMgr.isMacroBodyExpansion(ExprLoc) &&
+ !(isa<CallExpr>(E->IgnoreParens()) &&
+ E->getLocStart().isMacroID() &&
+ Lexer::isAtStartOfMacroExpansion(E->getLocStart(), SourceMgr,
+ getLangOpts()) &&
+ E->getLocEnd().isMacroID() &&
+ Lexer::isAtEndOfMacroExpansion(E->getLocEnd(), SourceMgr,
+ getLangOpts())))
return;
const Expr *WarnExpr;
Index: test/Sema/unused-expr.c
===================================================================
--- test/Sema/unused-expr.c
+++ test/Sema/unused-expr.c
@@ -132,6 +132,8 @@
#define M3(a) (t3(a), fn2())
#define M4(a, b) (foo((a), (b)) ? 0 : t3(a), 1)
#define M5(a, b) (foo((a), (b)), 1)
+#define M6() fn1()
+#define M7() (fn1())
void t11(int i, int j) {
M1(i, j); // no warning
NOP((long)foo(i, j)); // expected-warning {{expression result unused}}
@@ -143,10 +145,14 @@
NOP((foo(i, j) ? 0 : t3(i), 1)); // expected-warning {{expression result unused}}
M5(i, j); // no warning
NOP((foo(i, j), 1)); // expected-warning {{expression result unused}}
+ M6(); // expected-warning {{ignoring return value}}
+ M7(); // expected-warning {{ignoring return value}}
}
#undef NOP
#undef M1
#undef M2
#undef M3
#undef M4
#undef M5
+#undef M6
+#undef M7
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