llvm/include/llvm/ADT/DenseMap.h:1105:8: warning: stack usage is 279392 bytes [-Wstack-usage=]

[dcb314]

I just tried a clang build with -Wstack-usage switched on.

The winner for the most stack usage is the following code:

void grow(unsigned AtLeast) {

Would there be any value in reducing the stack usage of this function
downto about 64K, the next highest stack usage function ?

[topperc]

This is a method in a templated class. Do you happen to know the template parameters for the class?

[dcb314]

Do you happen to know the template parameters for the class?

No. The text in the build is

llvm/include/llvm/ADT/DenseMap.h: In member function ‘void llvm::SmallDenseMap<KeyT, ValueT, InlineBuckets, KeyInfoT, BucketT>::grow(unsigned int) [with KeyT = clang::Decl*; ValueT = llvm::SmallVector<llvm::SmallVector<clang::Decl*, 32>, 32>; unsigned int InlineBuckets = 32; KeyInfoT = llvm::DenseMapInfo<clang::Decl*, void>; BucketT = llvm::detail::DenseMapPair<clang::Decl*, llvm::SmallVector<llvm::SmallVector<clang::Decl*, 32>, 32> >]’:
/home/dcb40b/llvm/trunk/llvm/include/llvm/ADT/DenseMap.h:1105:8: warning: stack usage is 279392 bytes [-Wstack-usage=]

Pretty garbled to me. It might make some sense to you.

[topperc]

I believe the template parameters are

KeyT = clang::Decl*
ValueT = llvm::SmallVector<llvm::SmallVector<clang::Decl*, 32>, 32>
InlineBuckets = 32
KeyInfoT = llvm::DenseMapInfo<clang::Decl*, void>
BucketT = llvm::detail::DenseMapPair<clang::Decl*, llvm::SmallVector<llvm::SmallVector<clang::Decl*, 32>, 32>

The ValueT has a pretty large static size. At least 32 x 32 x 8 bytes. I suspect we're creating several of those on the stack in this function.

[topperc]

My best guess is its this map from clang/include/clang/AST/ASTImporter.h

    using SavedImportPathsForOneDecl =                                           
        llvm::SmallVector<ImportPathTy::VecTy, 32>;                              
    using SavedImportPathsTy =                                                   
        llvm::SmallDenseMap<Decl *, SavedImportPathsForOneDecl, 32>;             
    SavedImportPathsTy SavedImportPaths;