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Fix LSR compile time. 

This is a simple fix that brings the compilation time from 5min to 5s
on a specific real-world example. It's a large chain of computation in
a crypto routine (always a problem for SCEV). A unit test is not
feasible and there would be no way to check it. The fix is just basic
good practice for dealing with SCEVs, there's no risk of regression.

Patch by Daniel Reynaud!

llvm-svn: 220622
This commit is contained in:
Andrew Trick 2014-10-25 19:42:07 +00:00
parent 8cdf0425a0
commit 9ccbed5a12
1 changed files with 5 additions and 0 deletions
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5
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
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@ -3117,10 +3117,15 @@ void
LSRInstance::CollectLoopInvariantFixupsAndFormulae() {
SmallVector<const SCEV *, 8> Worklist(RegUses.begin(), RegUses.end());
SmallPtrSet<const SCEV *, 8> Inserted;
SmallPtrSet<const SCEV *, 32> Done;
while (!Worklist.empty()) {
const SCEV *S = Worklist.pop_back_val();
// Don't process the same SCEV twice
if (!Done.insert(S))
continue;
if (const SCEVNAryExpr *N = dyn_cast<SCEVNAryExpr>(S))
Worklist.append(N->op_begin(), N->op_end());
else if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))