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0665669876
https://reviews.llvm.org/D54188 marked "alias" targets as used in C to
fix -Wunused false positives. This patch extends the approach to handle
mangled names to support global scope names in C++ and the
`overloadable` attribute in C.
(Note: we should skip `UsingShadowDecl`, which would trigger an
assertion failure in `ItaniumMangleContextImpl::mangleCXXName`.
See regression test added by commit 1c2afbae9af22b58190c10e3517242d01d89d612.)
In addition, we mark ifunc targets as used to fix #63957 (temporarily
used by xz; ifunc was removed by
689ae24273)
While our approach has false negatives for namespace scope names, the
majority of alias/ifunc C++ uses (global scope with no overloads) are
handled.
Note: The following function with internal linkage but C language
linkage type is mangled in Clang but not in GCC. This inconsistency
makes alias/ifunc difficult to use in C++ with portability (#88593).
```
extern "C" {
static void f0() {}
// GCC: void g0() __attribute__((alias("_ZL2f0v")));
// Clang: void g0() __attribute__((alias("f0")));
}
```
Pull Request: https://github.com/llvm/llvm-project/pull/87130
53 lines
2.1 KiB
C++
53 lines
2.1 KiB
C++
// RUN: %clang_cc1 -triple x86_64-linux -Wunused -x c -verify %s
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// RUN: %clang_cc1 -triple x86_64-linux -Wunused -verify=expected,cxx %s
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#ifdef __cplusplus
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extern "C" {
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#endif
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static int f(void) { return 42; }
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int g(void) __attribute__((alias("f")));
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static int foo [] = { 42, 0xDEAD }; // cxx-warning{{variable 'foo' is not needed and will not be emitted}}
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extern typeof(foo) bar __attribute__((unused, alias("foo")));
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/// https://github.com/llvm/llvm-project/issues/88593
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/// We report a warning in C++ mode because the internal linkage `resolver` gets
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/// mangled as it does not have a language linkage. GCC does not mangle
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/// `resolver` or report a warning.
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static int (*resolver(void))(void) { return f; } // cxx-warning{{unused function 'resolver'}}
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int ifunc(void) __attribute__((ifunc("resolver")));
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static int __attribute__((overloadable)) f0(int x) { return x; }
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static float __attribute__((overloadable)) f0(float x) { return x; } // expected-warning{{unused function 'f0'}}
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int g0(void) __attribute__((alias("_ZL2f0i")));
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#ifdef __cplusplus
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static int f1() { return 42; }
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int g1(void) __attribute__((alias("_ZL2f1v")));
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}
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/// We demangle alias/ifunc target and mark all found functions as used.
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static int f2(int) { return 42; } // cxx-warning{{unused function 'f2'}}
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static int f2() { return 42; }
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int g2() __attribute__((alias("_ZL2f2v")));
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static int (*resolver1())() { return f; } // cxx-warning{{unused function 'resolver1'}}
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static int (*resolver1(int))() { return f; }
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int ifunc1() __attribute__((ifunc("_ZL9resolver1i")));
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/// TODO: We should report "unused function" for f3(int).
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namespace ns {
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static int f3(int) { return 42; } // cxx-warning{{unused function 'f3'}}
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static int f3() { return 42; } // cxx-warning{{unused function 'f3'}}
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int g3() __attribute__((alias("_ZN2nsL2f3Ev")));
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}
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template <class T>
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static void *f4(T) { return nullptr; }
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static void *f4() { return nullptr; } // cxx-warning{{unused function 'f4'}}
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extern void g4_int() __attribute__((ifunc("_ZL2f4IiEPvT_")));
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extern void g4_char() __attribute__((ifunc("_ZL2f4IcEPcT_"))); // rejected by CodeGen
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void *use4 = f4(0);
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#endif
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