[llvm-dev] Loop optimization

Doerfert, Johannes via llvm-dev llvm-dev at lists.llvm.org
Tue Aug 13 10:12:39 PDT 2019

Without testing it I'd say loop idiom recognition (Transforms/Scalar/LoopIdiomRecognize.h) is the one that should kick in and optimize this.

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Garba Peter via llvm-dev <llvm-dev at lists.llvm.org>
Sent: Tuesday, August 13, 2019 11:54
To: llvm-dev at lists.llvm.org
Subject: [llvm-dev] Loop optimization


I was wondering if there is an optimization pass in LLVM or Polly that can optimize this given loop:

int main(int argc, char* argv[]) {
                char s = 0;

                // Loop is setting s = argv[1][0];
                for (int i=0; i<argv[1][0]; i++) {

                printf("s = %c\n", s);

                return 0;


int main(int argc, char* argv[]) {
                // Optimized loop
                char s = argv[1][0];

                printf("s = %c\n", s);

                return 0;

Is there an optimization that can do this?
And if not, maybe someone knows what hinders the optimizer?!

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