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Luke Benes via llvm-dev

2021-Mar-01 23:58 UTC

[llvm-dev] False Negatives Wunused-function in clang found by gcc

By building llvm-project with gcc 7 and 10, I found multiple Wunused-function
warnings that clang 11/12 missed.

All of these warnings were recently introduced, and the authors fixed many of
them.   Any ideas why clang misses so many of this category? And why the ones
missed are recent changes to the llvm codebase?

-Luke


=========
 After dab953c8e44a2 with gcc 10.2.1, I see the following new warnings:

[ 65%] Building CXX object lib/Linker/CMakeFiles/LLVMLinker.dir/IRMover.cpp.o
/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1600:1: warning:
‘std::pair<llvm::Value*, llvm::Value*>
{anonymous}::DataFlowSanitizer::getShadowOriginAddress(llvm::Value*,
llvm::Align, llvm::Instruction*)’ defined but not used [-Wunused-function]
 1600 | DataFlowSanitizer::getShadowOriginAddress(Value *Addr, Align
InstAlignment,
      | ^~~~~~~~~~~~~~~~~
/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1510:6: warning:
‘void {anonymous}::DFSanFunction::setOrigin(llvm::Instruction*, llvm::Value*)’
defined but not used [-Wunused-function]
 1510 | void DFSanFunction::setOrigin(Instruction *I, Value *Origin) {
      |      ^~~~~~~~~~~~~
/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1476:8: warning:
‘llvm::Value* {anonymous}::DFSanFunction::getOrigin(llvm::Value*)’ defined but
not used [-Wunused-function]
 1476 | Value *DFSanFunction::getOrigin(Value *V) {
      |        ^~~~~~~~~~~~~
/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1469:8: warning:
‘llvm::Value* {anonymous}::DFSanFunction::getRetvalOriginTLS()’ defined but not
used [-Wunused-function]
 1469 | Value *DFSanFunction::getRetvalOriginTLS() { return DFS.RetvalOriginTLS;
}
      |        ^~~~~~~~~~~~~

FIX:
https://github.com/llvm/llvm-project/commit/9524632fa2bf8c894e4aac27f03631a1915d84d3

=========
After bc8e262afe83, with gcc 10.1 but not clang 11, I'm seeing:

[ 21%] Building CXX object
lib/MC/MCParser/CMakeFiles/LLVMMCParser.dir/MasmParser.cpp.o
/llvm/lib/MC/MCParser/MasmParser.cpp:3836:6: warning: ‘bool
{anonymous}::MasmParser::emitStructValue(const {anonymous}::StructInfo&)’
defined but not used [-Wunused-function]
 3836 | bool MasmParser::emitStructValue(const StructInfo &Structure) {
      |      ^~~~~~~~~~

FIX: https://reviews.llvm.org/D83898

=========
In 931a68f26b9a3, I'm seeing the following warning with gcc7 and gcc10:
[ 70%] Building CXX object
lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RegAllocPBQP.cpp.o
/llvm/lib/CodeGen/RegAllocFast.cpp:384:6: warning: ‘bool
{anonymous}::RegAllocFast::verifyRegStateMapping(const
{anonymous}::RegAllocFast::LiveReg&) const’ defined but not used
[-Wunused-function]
 bool RegAllocFast::verifyRegStateMapping(const LiveReg &LR) const {
      ^~~~~~~~~~~~

FIX: 0671a4c5087d40450603d9d26cf239f1a8b1367e

David Blaikie via llvm-dev

2021-Mar-02 01:22 UTC

head link

[llvm-dev] False Negatives Wunused-function in clang found by gcc

Not sure where the regression might've leaked in. But does seem to be
something to do with anonymous namespace support and member functions:
https://godbolt.org/z/zz8WP1



On Mon, Mar 1, 2021 at 5:12 PM Luke Benes via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
> By building llvm-project with gcc 7 and 10, I found multiple
> Wunused-function warnings that clang 11/12 missed.
>
> All of these warnings were recently introduced, and the authors fixed many
> of them.   Any ideas why clang misses so many of this category? And why the
> ones missed are recent changes to the llvm codebase?
>
> -Luke
>
>
> =========>
>  After dab953c8e44a2 with gcc 10.2.1, I see the following new warnings:
>
> [ 65%] Building CXX object
> lib/Linker/CMakeFiles/LLVMLinker.dir/IRMover.cpp.o
> /llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1600:1:
> warning: ‘std::pair<llvm::Value*, llvm::Value*>
> {anonymous}::DataFlowSanitizer::getShadowOriginAddress(llvm::Value*,
> llvm::Align, llvm::Instruction*)’ defined but not used [-Wunused-function]
>  1600 | DataFlowSanitizer::getShadowOriginAddress(Value *Addr, Align
> InstAlignment,
>       | ^~~~~~~~~~~~~~~~~
> /llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1510:6:
> warning: ‘void {anonymous}::DFSanFunction::setOrigin(llvm::Instruction*,
> llvm::Value*)’ defined but not used [-Wunused-function]
>  1510 | void DFSanFunction::setOrigin(Instruction *I, Value *Origin) {
>       |      ^~~~~~~~~~~~~
> /llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1476:8:
> warning: ‘llvm::Value* {anonymous}::DFSanFunction::getOrigin(llvm::Value*)’
> defined but not used [-Wunused-function]
>  1476 | Value *DFSanFunction::getOrigin(Value *V) {
>       |        ^~~~~~~~~~~~~
> /llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1469:8:
> warning: ‘llvm::Value* {anonymous}::DFSanFunction::getRetvalOriginTLS()’
> defined but not used [-Wunused-function]
>  1469 | Value *DFSanFunction::getRetvalOriginTLS() { return
> DFS.RetvalOriginTLS; }
>       |        ^~~~~~~~~~~~~
>
> FIX:
>
https://github.com/llvm/llvm-project/commit/9524632fa2bf8c894e4aac27f03631a1915d84d3
>
> =========>
> After bc8e262afe83, with gcc 10.1 but not clang 11, I'm seeing:
>
> [ 21%] Building CXX object
> lib/MC/MCParser/CMakeFiles/LLVMMCParser.dir/MasmParser.cpp.o
> /llvm/lib/MC/MCParser/MasmParser.cpp:3836:6: warning: ‘bool
> {anonymous}::MasmParser::emitStructValue(const
{anonymous}::StructInfo&)’
> defined but not used [-Wunused-function]
>  3836 | bool MasmParser::emitStructValue(const StructInfo &Structure) {
>       |      ^~~~~~~~~~
>
> FIX: https://reviews.llvm.org/D83898
>
> =========>
> In 931a68f26b9a3, I'm seeing the following warning with gcc7 and gcc10:
> [ 70%] Building CXX object
> lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RegAllocPBQP.cpp.o
> /llvm/lib/CodeGen/RegAllocFast.cpp:384:6: warning: ‘bool
> {anonymous}::RegAllocFast::verifyRegStateMapping(const
> {anonymous}::RegAllocFast::LiveReg&) const’ defined but not used
> [-Wunused-function]
>  bool RegAllocFast::verifyRegStateMapping(const LiveReg &LR) const {
>       ^~~~~~~~~~~~
>
> FIX: 0671a4c5087d40450603d9d26cf239f1a8b1367e
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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llvm dev - Mar 2021 - False Negatives Wunused-function in clang found by gcc

[llvm-dev] False Negatives Wunused-function in clang found by gcc

[llvm-dev] False Negatives Wunused-function in clang found by gcc