[llvm-dev] How to know pass dependencies?

Wang, Luyuan (MU-Student) via llvm-dev llvm-dev at lists.llvm.org
Mon Apr 22 20:54:27 PDT 2019

Dear LLVM developers,

I'm a beginner with LLVM, and I want to see how different loop optimization passes influence the performance. For example, I've generated IR code, and I would like to use "Loop Interchange" as the only loop optimization pass.

However, when I simply used `opt -loop-interchange input.ll -S -o output.ll` command, the IR code didn't change. I guess the reason may be the "-loop-interchange" pass also depends on other passes, so I should also specify some other passes before the loop interchange pass. But how do I know these dependencies?

Here is my C program to test loop interchange:

int main() {
  int i=0;
  int j=0;
  int a[333][222];
  for (i=0; i <222; i++) {
        for (j=0; j <333; j++) {
                a[j][i] = i * j;
  return 0;

I also tried this command, but still no influence:

opt -mem2reg -simplifycfg -loops -lcssa -loop-simplify -loop-rotate -loop-
interchange input.ll -S -o output.ll

Thank you so much.


Luyuan Wang

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