[LLVMdev] IndVarSimplify too aggressive ?

[Arnaud Allard de Grandmaison]

Hi all,

The IndVarSimplify pass seems to be too aggressive when it enlarge the induction variable type ; this can pessimize the generated code when the new induction variable size is not natively supported by the target. This is probably not an issue for x86_64, which supports natively all types, but it is a real one for several embedded targets, with very few native types.

I attached a patch to address this issue; if TargetData is available, the patch attempts to keep the induction variable to a native type when going thru the induction variable users.

Also attached my test-case in C, as well as the resulting assembly output, with and without the patch applied, for arm and x86_32 targets. You will note the loop instructions count can be reduced by 30% in several cases.

The patch could probably be made smarter : I am welcoming all suggestions.

Best Regards,
--
Arnaud de Grandmaison
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