forked from OSchip/llvm-project
[LoopFlatten] Fix missed LoopFlatten opportunity
When the limit of the inner loop is a known integer, the InstCombine pass now causes the transformation e.g. imcp ult i32 %inc, tripcount -> icmp ult %j, tripcount-step (where %j is the inner loop induction variable and %inc is add %j, step), which is now accounted for when identifying the trip count of the loop. This is also an acceptable use of %j (provided the step is 1) so is ignored as long as the compare that it's used in is also the condition of the inner branch. Differential Revision: https://reviews.llvm.org/D105802
This commit is contained in:
Rosie Sumpter
parent
23d4c4f3fb
commit
f117ed542f
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@ -167,8 +167,7 @@ static bool findLoopComponents(
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// count computed by SCEV then this is either because the trip count variable
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// has been widened (then leave the trip count as it is), or because it is a
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// constant and another transformation has changed the compare, e.g.
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// icmp ult %inc, tripcount -> icmp ult %j, tripcount-1, then we don't flatten
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// the loop (yet).
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// icmp ult %inc, tripcount -> icmp ult %j, tripcount-1.
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TripCount = Compare->getOperand(1);
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const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
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if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
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@ -176,12 +175,22 @@ static bool findLoopComponents(
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return false;
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}
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const SCEV *SCEVTripCount = SE->getTripCountFromExitCount(BackedgeTakenCount);
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if (SE->getSCEV(TripCount) != SCEVTripCount) {
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if (!IsWidened) {
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if (SE->getSCEV(TripCount) != SCEVTripCount && !IsWidened) {
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ConstantInt *RHS = dyn_cast<ConstantInt>(TripCount);
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if (!RHS) {
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LLVM_DEBUG(dbgs() << "Could not find valid trip count\n");
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return false;
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}
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auto TripCountInst = dyn_cast<Instruction>(TripCount);
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// The L->isCanonical check above ensures we only get here if the loop
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// increments by 1 on each iteration, so the RHS of the Compare is
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// tripcount-1 (i.e equivalent to the backedge taken count).
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assert(SE->getSCEV(RHS) == BackedgeTakenCount &&
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"Expected RHS of compare to be equal to the backedge taken count");
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ConstantInt *One = ConstantInt::get(RHS->getType(), 1);
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TripCount = ConstantInt::get(TripCount->getContext(),
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RHS->getValue() + One->getValue());
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} else if (SE->getSCEV(TripCount) != SCEVTripCount) {
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auto *TripCountInst = dyn_cast<Instruction>(TripCount);
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if (!TripCountInst) {
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LLVM_DEBUG(dbgs() << "Could not find valid extended trip count\n");
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return false;
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@ -368,6 +377,13 @@ static bool checkIVUsers(FlattenInfo &FI) {
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U = *U->user_begin();
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}
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// If the use is in the compare (which is also the condition of the inner
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// branch) then the compare has been altered by another transformation e.g
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// icmp ult %inc, tripcount -> icmp ult %j, tripcount-1, where tripcount is
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// a constant. Ignore this use as the compare gets removed later anyway.
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if (U == FI.InnerBranch->getCondition())
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continue;
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LLVM_DEBUG(dbgs() << "Found use of inner induction variable: "; U->dump());
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Value *MatchedMul;
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@ -341,38 +341,111 @@ for.end8: ; preds = %for.inc6
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ret i32 10
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}
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; When the loop trip count is a constant (e.g. 20) and the step size is
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; 1, InstCombine causes the transformation icmp ult i32 %inc, 20 ->
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; icmp ult i32 %j, 19. In this case a valid trip count is not found so
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; the loop is not flattened.
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define i32 @test9(i32* nocapture %A) {
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; test_10, test_11 and test_12 are for the case when the
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; inner trip count is a constant, then the InstCombine pass
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; makes the transformation icmp ult i32 %inc, tripcount ->
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; icmp ult i32 %j, tripcount-step.
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; test_10: The step is not 1.
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define i32 @test_10(i32* nocapture %A) {
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entry:
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br label %for.cond1.preheader
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for.cond1.preheader:
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%i.017 = phi i32 [ 0, %entry ], [ %inc6, %for.cond.cleanup3 ]
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%i.017 = phi i32 [ 0, %entry ], [ %inc, %for.cond.cleanup3 ]
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%mul = mul i32 %i.017, 20
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br label %for.body4
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for.cond.cleanup3:
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%inc6 = add i32 %i.017, 1
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%cmp = icmp ult i32 %inc6, 11
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br i1 %cmp, label %for.cond1.preheader, label %for.cond.cleanup
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for.body4:
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%j.016 = phi i32 [ 0, %for.cond1.preheader ], [ %inc, %for.body4 ]
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%j.016 = phi i32 [ 0, %for.cond1.preheader ], [ %add5, %for.body4 ]
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%add = add i32 %j.016, %mul
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%arrayidx = getelementptr inbounds i32, i32* %A, i32 %add
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store i32 30, i32* %arrayidx, align 4
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%inc = add nuw nsw i32 %j.016, 1
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%cmp2 = icmp ult i32 %j.016, 19
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%add5 = add nuw nsw i32 %j.016, 2
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%cmp2 = icmp ult i32 %j.016, 18
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br i1 %cmp2, label %for.body4, label %for.cond.cleanup3
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for.cond.cleanup3:
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%inc = add i32 %i.017, 1
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%cmp = icmp ult i32 %inc, 11
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br i1 %cmp, label %for.cond1.preheader, label %for.cond.cleanup
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for.cond.cleanup:
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%0 = load i32, i32* %A, align 4
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ret i32 %0
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}
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; test_11: The inner inducation variable is used in a compare which
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; isn't the condition of the inner branch.
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define i32 @test_11(i32* nocapture %A) {
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entry:
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br label %for.cond1.preheader
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for.cond1.preheader:
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%i.020 = phi i32 [ 0, %entry ], [ %inc7, %for.cond.cleanup3 ]
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%mul = mul i32 %i.020, 20
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br label %for.body4
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for.body4:
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%j.019 = phi i32 [ 0, %for.cond1.preheader ], [ %inc, %for.body4 ]
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%cmp5 = icmp ult i32 %j.019, 5
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%cond = select i1 %cmp5, i32 30, i32 15
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%add = add i32 %j.019, %mul
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%arrayidx = getelementptr inbounds i32, i32* %A, i32 %add
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store i32 %cond, i32* %arrayidx, align 4
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%inc = add nuw nsw i32 %j.019, 1
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%cmp2 = icmp ult i32 %j.019, 19
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br i1 %cmp2, label %for.body4, label %for.cond.cleanup3
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for.cond.cleanup3:
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%inc7 = add i32 %i.020, 1
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%cmp = icmp ult i32 %inc7, 11
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br i1 %cmp, label %for.cond1.preheader, label %for.cond.cleanup
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for.cond.cleanup:
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%0 = load i32, i32* %A, align 4
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ret i32 %0
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}
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; test_12: Incoming phi node value for preheader is a variable
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define i32 @test_12(i32* %A) {
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entry:
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br label %while.cond1.preheader
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while.cond1.preheader:
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%j.017 = phi i32 [ 0, %entry ], [ %j.1, %while.end ]
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%i.016 = phi i32 [ 0, %entry ], [ %inc4, %while.end ]
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%mul = mul i32 %i.016, 20
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%cmp214 = icmp ult i32 %j.017, 20
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br i1 %cmp214, label %while.body3.preheader, label %while.end
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while.body3.preheader:
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br label %while.body3
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while.body3:
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%j.115 = phi i32 [ %inc, %while.body3 ], [ %j.017, %while.body3.preheader ]
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%add = add i32 %j.115, %mul
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%arrayidx = getelementptr inbounds i32, i32* %A, i32 %add
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store i32 30, i32* %arrayidx, align 4
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%inc = add nuw nsw i32 %j.115, 1
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%cmp2 = icmp ult i32 %j.115, 19
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br i1 %cmp2, label %while.body3, label %while.end.loopexit
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while.end.loopexit:
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%inc.lcssa = phi i32 [ %inc, %while.body3 ]
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br label %while.end
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while.end:
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%j.1 = phi i32 [ %j.017, %while.cond1.preheader], [ %inc.lcssa, %while.end.loopexit ]
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%inc4 = add i32 %i.016, 1
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%cmp = icmp ult i32 %inc4, 11
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br i1 %cmp, label %while.cond1.preheader, label %while.end5
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while.end5:
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%0 = load i32, i32* %A, align 4
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ret i32 %0
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}
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; Outer loop conditional phi
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define i32 @e() {
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entry:
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@ -683,5 +756,36 @@ for.body7:
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br i1 %cmp4, label %for.body7, label %for.cond.cleanup6.loopexit
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}
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; Invalid trip count
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define void @invalid_tripCount(i8* %a, i32 %b, i32 %c, i32 %initial-mutations, i32 %statemutations) {
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entry:
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%iszero = icmp eq i32 %b, 0
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br i1 %iszero, label %for.empty, label %for.loopinit
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for.loopinit:
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br label %for.loopbody.outer
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for.loopbody.outer:
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%for.count.ph = phi i32 [ %c, %for.refetch ], [ %b, %for.loopinit ]
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br label %for.loopbody
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for.loopbody:
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%for.index = phi i32 [ %1, %for.notmutated ], [ 0, %for.loopbody.outer ]
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%0 = icmp eq i32 %statemutations, %initial-mutations
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br i1 %0, label %for.notmutated, label %for.mutated
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for.mutated:
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call void @objc_enumerationMutation(i8* %a)
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br label %for.notmutated
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for.notmutated:
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%1 = add nuw i32 %for.index, 1
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%2 = icmp ult i32 %1, %for.count.ph
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br i1 %2, label %for.loopbody, label %for.refetch
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for.refetch:
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%3 = icmp eq i32 %c, 0
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br i1 %3, label %for.empty.loopexit, label %for.loopbody.outer
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for.empty.loopexit:
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br label %for.empty
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for.empty:
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ret void
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}
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declare void @objc_enumerationMutation(i8*)
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declare dso_local void @f(i32*)
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declare dso_local void @g(...)
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@ -586,6 +586,59 @@ for.end8: ; preds = %for.inc6
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ret i32 10
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}
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; When the inner loop trip count is a constant and the step
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; is 1, the InstCombine pass causes the transformation e.g.
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; icmp ult i32 %inc, 20 -> icmp ult i32 %j, 19. This doesn't
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; match the pattern (OuterPHI * InnerTripCount) + InnerPHI but
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; we should still flatten the loop as the compare is removed
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; later anyway.
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define i32 @test9(i32* nocapture %A) {
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entry:
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br label %for.cond1.preheader
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; CHECK-LABEL: test9
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; CHECK: entry:
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; CHECK: %flatten.tripcount = mul i32 20, 11
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; CHECK: br label %for.cond1.preheader
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for.cond1.preheader:
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%i.017 = phi i32 [ 0, %entry ], [ %inc6, %for.cond.cleanup3 ]
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%mul = mul i32 %i.017, 20
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br label %for.body4
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; CHECK: for.cond1.preheader:
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; CHECK: %i.017 = phi i32 [ 0, %entry ], [ %inc6, %for.cond.cleanup3 ]
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; CHECK: %mul = mul i32 %i.017, 20
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; CHECK: br label %for.body4
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for.cond.cleanup3:
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%inc6 = add i32 %i.017, 1
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%cmp = icmp ult i32 %inc6, 11
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br i1 %cmp, label %for.cond1.preheader, label %for.cond.cleanup
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; CHECK: for.cond.cleanup3:
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; CHECK: %inc6 = add i32 %i.017, 1
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; CHECK: %cmp = icmp ult i32 %inc6, %flatten.tripcount
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; CHECK: br i1 %cmp, label %for.cond1.preheader, label %for.cond.cleanup
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for.body4:
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%j.016 = phi i32 [ 0, %for.cond1.preheader ], [ %inc, %for.body4 ]
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%add = add i32 %j.016, %mul
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%arrayidx = getelementptr inbounds i32, i32* %A, i32 %add
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store i32 30, i32* %arrayidx, align 4
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%inc = add nuw nsw i32 %j.016, 1
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%cmp2 = icmp ult i32 %j.016, 19
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br i1 %cmp2, label %for.body4, label %for.cond.cleanup3
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; CHECK: for.body4
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; CHECK: %j.016 = phi i32 [ 0, %for.cond1.preheader ]
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; CHECK: %add = add i32 %j.016, %mul
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; CHECK: %arrayidx = getelementptr inbounds i32, i32* %A, i32 %i.017
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; CHECK: store i32 30, i32* %arrayidx, align 4
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; CHECK: %inc = add nuw nsw i32 %j.016, 1
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; CHECK: %cmp2 = icmp ult i32 %j.016, 19
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; CHECK: br label %for.cond.cleanup3
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for.cond.cleanup:
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%0 = load i32, i32* %A, align 4
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ret i32 %0
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}
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declare i32 @func(i32)
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