CODEWITHSUNDEEP
clangllvmllvm-clangllvm-ir
Y. Tseng
Y. Tseng

Reputation: 51

Convert LLVM IR to higher optimization level

I have compiled the C code to LLVM IR code with -O0 optimization.

How can I convert this -O0 LLVM IR code to the -O3 LLVM IR code "without the C code"?

I have tried below:

clang -O3 -S -emit-llvm O0.ll -o O3.ll

and

opt -O3 -S O0.ll -o O3.ll

but the output is still -O0 level.

Thank you.

Upvotes: 4

Views: 935

Answers (1)

compor
compor

Reputation: 2339

I'm not sure when the change happened (I think it's LLVM 3.9.0 and on), but when you compile to bitcode functions get annotated with the optnone attribute and further optimizations are not performed.

Have a look for a relevant SO discussion here.

What is suggested is to do this:

clang -emit-llvm -O1 -mllvm -disable-llvm-optzns -disable-llvm-passes foo.c -o foo.bc

For LLVM 3.8.0 and earlier (I think) what you have already been doing is enough.

So, once you obtain that bitcode (without the optnone) argument, you can use opt as you've already been doing.

Upvotes: 1

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