Generate an optimized AST using clang and libclang

Question

I want to apply clang optimizations to a source file then generate its AST. I tried passing -O3 flag but it seems that it is ignored.

For example I assume that for this snipped of program:

#include <stdio.h>
int main(void) {
  int a = 5 + 5;
  for (int i = 0; i < 10; i++) { }
  printf("%i\n", a);
  return 0;
}

Many optimizations can be applied, like removing the for loop converting 5 + 5 to 10.

When I dump the AST using clang -O3 -Xclang -ast-dump -fsyntax-only a.c I get the same AST without the optimization flag.

My goal is create a TranslationUnit with flag optimizations passed.

score 2 · Answer 1 · answered Mar 15 '18 at 13:31

2

Maybe optimizations don't result into another AST? See if what you are looking for are IR dumps after each llvm optimization.

answered Mar 15 '18 at 13:31

Not really. What I am looking for is an optimized AST. – user2232305 Mar 16 '18 at 11:27
4

First, the program is lowered from AST to IR. Second, optimization is performed on the IR. There is no such thing as 'optimized AST'. – Some Who Call Me Tim Mar 18 '18 at 15:29

1 Answers1