[llvm-dev] IR "canonicalization"

[Lorenzo Laneve via llvm-dev]

I’m implementing a front-end compiler and I need to do the most basic optimizations to the IR it generates, just like Clang does.

For example:

"if not x” becomes:

%1 = xor %x, true
br i1 %1 label %2, label %3

and Clang (even with -O0) just swaps labels:

bt i1 %x label %3, label %2



Another optimization is to remove “empty blocks” that simply br to another label:

br i1 %x label %emp1, label %emp2 

emp1:
	br label %cont

emp2:
	…

which becomes simply:

br i1 %x label %cont, label %emp2 

emp2:
	…


Is there a pass Clang uses to do these basic optimizations? Where should I look in the Clang source code?