CODEWITHSUNDEEP
clangllvm-clangllvm-ir
cgcgbcbc
cgcgbcbc

Reputation: 549

Why implicit free's declaration is taken vararg parameter in llvm

Taken the following code

int main() {
  int* a = (int*) malloc(sizeof(int) * 10);
  free(a);
  return 0;
}

If compile it to llvm IR by clang -S -emit-llvm -O0 -g, free's declaration is:

declare i32 @free(...) #2

However, if I add #include <stdlib.h>, free's declaration is:

declare void @free(i8*) #2

By adding include, the declaration is obviously taken from the header file, but why implicit free's declaration is different?

Upvotes: 1

Views: 62

Answers (1)

Mike Kinghan
Mike Kinghan

Reputation: 61575

In C (when permitted by the operative C Standard) the implied type of a function foo that is called without a prior prototype or definition is int foo(), which in C means function taking unspecified arguments, returning int. Implicit declaration of functions is illegal as of C99 and always illegal in C++.

If you compiled exactly that code with exactly those options you will have seen warnings for the implicit declarations of malloc and free, although they do not make it clear what the implied types are. If you compiled with with clang++ instead of clang you would have seen two errors.

Upvotes: 2

Related Questions