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-rw-r--r--llvm/lib/Transforms/Scalar/GuardWidening.cpp38
-rw-r--r--llvm/test/Transforms/GuardWidening/loop-schedule.ll33
2 files changed, 56 insertions, 15 deletions
diff --git a/llvm/lib/Transforms/Scalar/GuardWidening.cpp b/llvm/lib/Transforms/Scalar/GuardWidening.cpp
index 92e677db856..55d2f6ee81c 100644
--- a/llvm/lib/Transforms/Scalar/GuardWidening.cpp
+++ b/llvm/lib/Transforms/Scalar/GuardWidening.cpp
@@ -65,7 +65,7 @@ namespace {
class GuardWideningImpl {
DominatorTree &DT;
- PostDominatorTree &PDT;
+ PostDominatorTree *PDT;
LoopInfo &LI;
/// Together, these describe the region of interest. This might be all of
@@ -214,7 +214,7 @@ class GuardWideningImpl {
public:
- explicit GuardWideningImpl(DominatorTree &DT, PostDominatorTree &PDT,
+ explicit GuardWideningImpl(DominatorTree &DT, PostDominatorTree *PDT,
LoopInfo &LI, DomTreeNode *Root,
std::function<bool(BasicBlock*)> BlockFilter)
: DT(DT), PDT(PDT), LI(LI), Root(Root), BlockFilter(BlockFilter) {}
@@ -353,9 +353,8 @@ GuardWideningImpl::WideningScore GuardWideningImpl::computeWideningScore(
// 2) we have the extra cost of computing the guard condition in the common
// case. At the moment, we really only consider the second in our heuristic
// here. TODO: evaluate cost model for spurious deopt
- bool HoistingOutOfIf =
- !PDT.dominates(DominatedGuard->getParent(), DominatingGuard->getParent());
-
+ // NOTE: As written, this also lets us hoist right over another guard which
+ // is essentially just another spelling for control flow.
if (isWideningCondProfitable(DominatedGuard->getArgOperand(0),
DominatingGuard->getArgOperand(0)))
return HoistingOutOfLoop ? WS_VeryPositive : WS_Positive;
@@ -363,7 +362,26 @@ GuardWideningImpl::WideningScore GuardWideningImpl::computeWideningScore(
if (HoistingOutOfLoop)
return WS_Positive;
- return HoistingOutOfIf ? WS_IllegalOrNegative : WS_Neutral;
+ // Returns true if we might be hoisting above explicit control flow. Note
+ // that this completely ignores implicit control flow (guards, calls which
+ // throw, etc...). That choice appears arbitrary.
+ auto MaybeHoistingOutOfIf = [&]() {
+ auto *DominatingBlock = DominatingGuard->getParent();
+ auto *DominatedBlock = DominatedGuard->getParent();
+
+ // Same Block?
+ if (DominatedBlock == DominatingBlock)
+ return false;
+ // Obvious successor (common loop header/preheader case)
+ if (DominatedBlock == DominatingBlock->getUniqueSuccessor())
+ return false;
+ // TODO: diamond, triangle cases
+ if (!PDT) return true;
+ return !PDT->dominates(DominatedGuard->getParent(),
+ DominatingGuard->getParent());
+ };
+
+ return MaybeHoistingOutOfIf() ? WS_IllegalOrNegative : WS_Neutral;
}
bool GuardWideningImpl::isAvailableAt(Value *V, Instruction *Loc,
@@ -671,7 +689,7 @@ PreservedAnalyses GuardWideningPass::run(Function &F,
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
auto &LI = AM.getResult<LoopAnalysis>(F);
auto &PDT = AM.getResult<PostDominatorTreeAnalysis>(F);
- if (!GuardWideningImpl(DT, PDT, LI, DT.getRootNode(),
+ if (!GuardWideningImpl(DT, &PDT, LI, DT.getRootNode(),
[](BasicBlock*) { return true; } ).run())
return PreservedAnalyses::all();
@@ -694,7 +712,7 @@ struct GuardWideningLegacyPass : public FunctionPass {
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
- return GuardWideningImpl(DT, PDT, LI, DT.getRootNode(),
+ return GuardWideningImpl(DT, &PDT, LI, DT.getRootNode(),
[](BasicBlock*) { return true; } ).run();
}
@@ -720,7 +738,8 @@ struct LoopGuardWideningLegacyPass : public LoopPass {
return false;
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
- auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
+ auto *PDTWP = getAnalysisIfAvailable<PostDominatorTreeWrapperPass>();
+ auto *PDT = PDTWP ? &PDTWP->getPostDomTree() : nullptr;
BasicBlock *RootBB = L->getLoopPredecessor();
if (!RootBB)
RootBB = L->getHeader();
@@ -734,7 +753,6 @@ struct LoopGuardWideningLegacyPass : public LoopPass {
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
getLoopAnalysisUsage(AU);
- AU.addRequired<PostDominatorTreeWrapperPass>();
AU.addPreserved<PostDominatorTreeWrapperPass>();
}
};
diff --git a/llvm/test/Transforms/GuardWidening/loop-schedule.ll b/llvm/test/Transforms/GuardWidening/loop-schedule.ll
index 163fb521d47..94d1c863eac 100644
--- a/llvm/test/Transforms/GuardWidening/loop-schedule.ll
+++ b/llvm/test/Transforms/GuardWidening/loop-schedule.ll
@@ -3,13 +3,8 @@
; Main point of this test is to check the scheduling -- there should be
; no analysis passes needed between LICM and LoopGuardWidening
-; TODO: Because guard widdening currently requires post-dom, we end up
-; breaking the loop pass manager to compute it. Need to either make all
-; loop passes preserve postdom (hard) or make it optional in guard widdening
; CHECK: Loop Pass Manager
; CHECK: Loop Invariant Code Motion
-; CHECK: Post-Dominator Tree Construction
-; CHECK: Loop Pass Manager
; CHECK: Widen guards (within a single loop, as a loop pass)
; CHECK: Loop Invariant Code Motion
@@ -21,6 +16,7 @@ define void @iter(i32 %a, i32 %b, i1* %c_p) {
; CHECK: %cond_1 = icmp ult i32 %b, 10
; CHECK: %wide.chk = and i1 %cond_0, %cond_1
; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk) [ "deopt"() ]
+; CHECK-LABEL: loop:
entry:
%cond_0 = icmp ult i32 %a, 10
@@ -39,3 +35,30 @@ leave.loopexit: ; preds = %loop
leave: ; preds = %leave.loopexit, %entry
ret void
}
+
+define void @within_loop(i32 %a, i32 %b, i1* %c_p) {
+; CHECK-LABEL @within_loop
+; CHECK: %cond_0 = icmp ult i32 %a, 10
+; CHECK: %cond_1 = icmp ult i32 %b, 10
+; CHECK: %wide.chk = and i1 %cond_0, %cond_1
+; CHECK-LABEL: loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk) [ "deopt"() ]
+
+entry:
+ br label %loop
+
+loop: ; preds = %loop.preheader, %loop
+ %cond_0 = icmp ult i32 %a, 10
+ call void (i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ]
+ %cond_1 = icmp ult i32 %b, 10
+ call void (i1, ...) @llvm.experimental.guard(i1 %cond_1) [ "deopt"() ]
+ %cnd = load i1, i1* %c_p
+ br i1 %cnd, label %loop, label %leave.loopexit
+
+leave.loopexit: ; preds = %loop
+ br label %leave
+
+leave: ; preds = %leave.loopexit, %entry
+ ret void
+}
+
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