[llvm-dev] question about llvm partial unrolling/runtime unrolling
Frances Tzeng via llvm-dev
llvm-dev at lists.llvm.org
Mon Oct 12 16:13:25 PDT 2015
I am trying to do loop unrolling with loops that don't have constant loop
counter. It is highly appreciated if anyone can help me on this.
What I want to do is to turn
I set allowPartial and Runtime to both 1 (
llvm::createLoopUnrollPass(Threshold, count, 1, 1) )
Also overload the UnrollingPreferences structure to gives values to all
the Partial* members, but the loop still doesn't unroll.
The unrolling process hits this code in LoopUnrollRuntime.cpp
// Only unroll loops with a computable trip count and the trip count needs
// to be an int value (allowing a pointer type is a TODO item)
const SCEV *BECountSC = SE->getBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(BECountSC) ||
BECountSC=0xcccccccc and returns false here.
Based on the comments it looks like I still need a constant loop counter.
Is there a way to unroll with non-constant loop counter as in the example
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