forked from OSchip/llvm-project
Add -unroll-allow-partial command line option that enabled the loop unroller to
partially unroll a loop when fully unrolling would not fit under the threshold. Patch by Mikael Lepistö. llvm-svn: 54160
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llvm
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@ -33,6 +33,11 @@ static cl::opt<unsigned>
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UnrollCount("unroll-count", cl::init(0), cl::Hidden,
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cl::desc("Use this unroll count for all loops, for testing purposes"));
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static cl::opt<bool>
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UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden,
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cl::desc("Allows loops to be partially unrolled until "
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"-unroll-threshold loop size is reached."));
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namespace {
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class VISIBILITY_HIDDEN LoopUnroll : public LoopPass {
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public:
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@ -122,7 +127,8 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
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if (Count == 0) {
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// Conservative heuristic: if we know the trip count, see if we can
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// completely unroll (subject to the threshold, checked below); otherwise
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// don't unroll.
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// try to find greatest modulo of the trip count which is still under
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// threshold value.
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if (TripCount != 0) {
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Count = TripCount;
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} else {
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@ -136,9 +142,25 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
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DOUT << " Loop Size = " << LoopSize << "\n";
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uint64_t Size = (uint64_t)LoopSize*Count;
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if (TripCount != 1 && Size > UnrollThreshold) {
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DOUT << " TOO LARGE TO UNROLL: "
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<< Size << ">" << UnrollThreshold << "\n";
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DOUT << " Too large to fully unroll with count: " << Count
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<< " because size: " << Size << ">" << UnrollThreshold << "\n";
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if (UnrollAllowPartial) {
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// Reduce unroll count to be modulo of TripCount for partial unrolling
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Count = UnrollThreshold / LoopSize;
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while (Count != 0 && TripCount%Count != 0) {
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Count--;
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}
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if (Count < 2) {
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DOUT << " could not unroll partially\n";
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return false;
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} else {
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DOUT << " partially unrolling with count: " << Count << "\n";
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}
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} else {
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DOUT << " will not try to unroll partially because "
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<< "-unroll-allow-partial not given\n";
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return false;
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}
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}
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}
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@ -0,0 +1,15 @@
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; RUN: llvm-as < %s | opt -debug -loop-unroll |& grep {will not try to unroll partially because}
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; RUN: llvm-as < %s | opt -debug -loop-unroll -unroll-allow-partial |& grep {partially unrolling with count}
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; RUN: llvm-as < %s | opt -debug -loop-unroll -unroll-allow-partial -unroll-threshold=3 |& grep {could not unroll partially}
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define i32 @main() {
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entry:
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br label %no_exit
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no_exit: ; preds = %no_exit, %entry
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%indvar = phi i32 [ 0, %entry ], [ %indvar.next, %no_exit ] ; <i32> [#uses=1]
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%indvar.next = add i32 %indvar, 1 ; <i32> [#uses=2]
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%exitcond = icmp ne i32 %indvar.next, 100 ; <i1> [#uses=1]
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br i1 %exitcond, label %no_exit, label %loopexit
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loopexit: ; preds = %no_exit
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ret i32 0
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}
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