[llvm] r372223 - [SDA] Don't stop divergence propagation at the IPD.
Jay Foad via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 18 06:40:22 PDT 2019
Author: foad
Date: Wed Sep 18 06:40:22 2019
New Revision: 372223
URL: http://llvm.org/viewvc/llvm-project?rev=372223&view=rev
Log:
[SDA] Don't stop divergence propagation at the IPD.
Summary:
This fixes B42473 and B42706.
This patch makes the SDA propagate branch divergence until the end of the RPO traversal. Before, the SyncDependenceAnalysis propagated divergence only until the IPD in rpo order. RPO is incompatible with post dominance in the presence of loops. This made the SDA crash because blocks were missed in the propagation.
Reviewers: foad, nhaehnle
Reviewed By: foad
Subscribers: jvesely, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D65274
Added:
llvm/trunk/test/Analysis/DivergenceAnalysis/AMDGPU/b42473-r1-crash.ll
Modified:
llvm/trunk/lib/Analysis/SyncDependenceAnalysis.cpp
Modified: llvm/trunk/lib/Analysis/SyncDependenceAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/SyncDependenceAnalysis.cpp?rev=372223&r1=372222&r2=372223&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/SyncDependenceAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/SyncDependenceAnalysis.cpp Wed Sep 18 06:40:22 2019
@@ -218,9 +218,11 @@ struct DivergencePropagator {
template <typename SuccessorIterable>
std::unique_ptr<ConstBlockSet>
computeJoinPoints(const BasicBlock &RootBlock,
- SuccessorIterable NodeSuccessors, const Loop *ParentLoop, const BasicBlock * PdBoundBlock) {
+ SuccessorIterable NodeSuccessors, const Loop *ParentLoop) {
assert(JoinBlocks);
+ LLVM_DEBUG(dbgs() << "SDA:computeJoinPoints. Parent loop: " << (ParentLoop ? ParentLoop->getName() : "<null>") << "\n" );
+
// bootstrap with branch targets
for (const auto *SuccBlock : NodeSuccessors) {
DefMap.emplace(SuccBlock, SuccBlock);
@@ -228,13 +230,19 @@ struct DivergencePropagator {
if (ParentLoop && !ParentLoop->contains(SuccBlock)) {
// immediate loop exit from node.
ReachedLoopExits.insert(SuccBlock);
- continue;
} else {
// regular successor
PendingUpdates.insert(SuccBlock);
}
}
+ LLVM_DEBUG(
+ dbgs() << "SDA: rpo order:\n";
+ for (const auto * RpoBlock : FuncRPOT) {
+ dbgs() << "- " << RpoBlock->getName() << "\n";
+ }
+ );
+
auto ItBeginRPO = FuncRPOT.begin();
// skip until term (TODO RPOT won't let us start at @term directly)
@@ -245,16 +253,18 @@ struct DivergencePropagator {
// propagate definitions at the immediate successors of the node in RPO
auto ItBlockRPO = ItBeginRPO;
- while (++ItBlockRPO != ItEndRPO && *ItBlockRPO != PdBoundBlock) {
+ while ((++ItBlockRPO != ItEndRPO) &&
+ !PendingUpdates.empty()) {
const auto *Block = *ItBlockRPO;
+ LLVM_DEBUG(dbgs() << "SDA::joins. visiting " << Block->getName() << "\n");
- // skip @block if not pending update
+ // skip Block if not pending update
auto ItPending = PendingUpdates.find(Block);
if (ItPending == PendingUpdates.end())
continue;
PendingUpdates.erase(ItPending);
- // propagate definition at @block to its successors
+ // propagate definition at Block to its successors
auto ItDef = DefMap.find(Block);
const auto *DefBlock = ItDef->second;
assert(DefBlock);
@@ -278,6 +288,8 @@ struct DivergencePropagator {
}
}
+ LLVM_DEBUG(dbgs() << "SDA::joins. After propagation:\n"; printDefs(dbgs()));
+
// We need to know the definition at the parent loop header to decide
// whether the definition at the header is different from the definition at
// the loop exits, which would indicate a divergent loop exits.
@@ -292,24 +304,17 @@ struct DivergencePropagator {
// |
// proper exit from both loops
//
- // D post-dominates B as it is the only proper exit from the "A loop".
- // If C has a divergent branch, propagation will therefore stop at D.
- // That implies that B will never receive a definition.
- // But that definition can only be the same as at D (D itself in thise case)
- // because all paths to anywhere have to pass through D.
- //
- const BasicBlock *ParentLoopHeader =
- ParentLoop ? ParentLoop->getHeader() : nullptr;
- if (ParentLoop && ParentLoop->contains(PdBoundBlock)) {
- DefMap[ParentLoopHeader] = DefMap[PdBoundBlock];
- }
-
// analyze reached loop exits
if (!ReachedLoopExits.empty()) {
+ const BasicBlock *ParentLoopHeader =
+ ParentLoop ? ParentLoop->getHeader() : nullptr;
+
assert(ParentLoop);
- const auto *HeaderDefBlock = DefMap[ParentLoopHeader];
+ auto ItHeaderDef = DefMap.find(ParentLoopHeader);
+ const auto *HeaderDefBlock = (ItHeaderDef == DefMap.end()) ? nullptr : ItHeaderDef->second;
+
LLVM_DEBUG(printDefs(dbgs()));
- assert(HeaderDefBlock && "no definition in header of carrying loop");
+ assert(HeaderDefBlock && "no definition at header of carrying loop");
for (const auto *ExitBlock : ReachedLoopExits) {
auto ItExitDef = DefMap.find(ExitBlock);
@@ -339,19 +344,10 @@ const ConstBlockSet &SyncDependenceAnaly
return *ItCached->second;
}
- // dont propagte beyond the immediate post dom of the loop
- const auto *PdNode = PDT.getNode(const_cast<BasicBlock *>(Loop.getHeader()));
- const auto *IpdNode = PdNode->getIDom();
- const auto *PdBoundBlock = IpdNode ? IpdNode->getBlock() : nullptr;
- while (PdBoundBlock && Loop.contains(PdBoundBlock)) {
- IpdNode = IpdNode->getIDom();
- PdBoundBlock = IpdNode ? IpdNode->getBlock() : nullptr;
- }
-
// compute all join points
DivergencePropagator Propagator{FuncRPOT, DT, PDT, LI};
auto JoinBlocks = Propagator.computeJoinPoints<const LoopExitVec &>(
- *Loop.getHeader(), LoopExits, Loop.getParentLoop(), PdBoundBlock);
+ *Loop.getHeader(), LoopExits, Loop.getParentLoop());
auto ItInserted = CachedLoopExitJoins.emplace(&Loop, std::move(JoinBlocks));
assert(ItInserted.second);
@@ -370,16 +366,11 @@ SyncDependenceAnalysis::join_blocks(cons
if (ItCached != CachedBranchJoins.end())
return *ItCached->second;
- // dont propagate beyond the immediate post dominator of the branch
- const auto *PdNode = PDT.getNode(const_cast<BasicBlock *>(Term.getParent()));
- const auto *IpdNode = PdNode->getIDom();
- const auto *PdBoundBlock = IpdNode ? IpdNode->getBlock() : nullptr;
-
// compute all join points
DivergencePropagator Propagator{FuncRPOT, DT, PDT, LI};
const auto &TermBlock = *Term.getParent();
auto JoinBlocks = Propagator.computeJoinPoints<succ_const_range>(
- TermBlock, successors(Term.getParent()), LI.getLoopFor(&TermBlock), PdBoundBlock);
+ TermBlock, successors(Term.getParent()), LI.getLoopFor(&TermBlock));
auto ItInserted = CachedBranchJoins.emplace(&Term, std::move(JoinBlocks));
assert(ItInserted.second);
Added: llvm/trunk/test/Analysis/DivergenceAnalysis/AMDGPU/b42473-r1-crash.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/DivergenceAnalysis/AMDGPU/b42473-r1-crash.ll?rev=372223&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/DivergenceAnalysis/AMDGPU/b42473-r1-crash.ll (added)
+++ llvm/trunk/test/Analysis/DivergenceAnalysis/AMDGPU/b42473-r1-crash.ll Wed Sep 18 06:40:22 2019
@@ -0,0 +1,111 @@
+; RUN: opt -mtriple amdgcn-unknown-amdhsa -analyze -divergence -use-gpu-divergence-analysis %s | FileCheck %s
+
+declare i32 @gf2(i32)
+declare i32 @gf1(i32)
+
+define void @tw1(i32 addrspace(4)* noalias nocapture readonly %A, i32 addrspace(4)* noalias nocapture %B) local_unnamed_addr #2 {
+; CHECK: Printing analysis 'Legacy Divergence Analysis' for function 'tw1':
+; CHECK: DIVERGENT: i32 addrspace(4)* %A
+; CHECK: DIVERGENT: i32 addrspace(4)* %B
+entry:
+; CHECK: DIVERGENT: %call = tail call i32 @gf2(i32 0) #0
+; CHECK: DIVERGENT: %cmp = icmp ult i32 %call, 16
+; CHECK: DIVERGENT: br i1 %cmp, label %if.then, label %new_exit
+ %call = tail call i32 @gf2(i32 0) #3
+ %cmp = icmp ult i32 %call, 16
+ br i1 %cmp, label %if.then, label %new_exit
+
+if.then:
+; CHECK: DIVERGENT: %call1 = tail call i32 @gf1(i32 0) #0
+; CHECK: DIVERGENT: %arrayidx = getelementptr inbounds i32, i32 addrspace(4)* %A, i32 %call1
+; CHECK: DIVERGENT: %0 = load i32, i32 addrspace(4)* %arrayidx, align 4
+; CHECK: DIVERGENT: %cmp225 = icmp sgt i32 %0, 0
+; CHECK: DIVERGENT: %arrayidx10 = getelementptr inbounds i32, i32 addrspace(4)* %B, i32 %call1
+; CHECK: DIVERGENT: br i1 %cmp225, label %while.body.preheader, label %if.then.while.end_crit_edge
+ %call1 = tail call i32 @gf1(i32 0) #4
+ %arrayidx = getelementptr inbounds i32, i32 addrspace(4)* %A, i32 %call1
+ %0 = load i32, i32 addrspace(4)* %arrayidx, align 4
+ %cmp225 = icmp sgt i32 %0, 0
+ %arrayidx10 = getelementptr inbounds i32, i32 addrspace(4)* %B, i32 %call1
+ br i1 %cmp225, label %while.body.preheader, label %if.then.while.end_crit_edge
+
+while.body.preheader:
+ br label %while.body
+
+if.then.while.end_crit_edge:
+; CHECK: DIVERGENT: %.pre = load i32, i32 addrspace(4)* %arrayidx10, align 4
+ %.pre = load i32, i32 addrspace(4)* %arrayidx10, align 4
+ br label %while.end
+
+while.body:
+; CHECK-NOT: DIVERGENT: %i.026 = phi i32 [ %inc, %if.end.while.body_crit_edge ], [ 0, %while.body.preheader ]
+; CHECK: DIVERGENT: %call3 = tail call i32 @gf1(i32 0) #0
+; CHECK: DIVERGENT: %cmp4 = icmp ult i32 %call3, 10
+; CHECK: DIVERGENT: %arrayidx6 = getelementptr inbounds i32, i32 addrspace(4)* %A, i32 %i.026
+; CHECK: DIVERGENT: %1 = load i32, i32 addrspace(4)* %arrayidx6, align 4
+; CHECK: DIVERGENT: br i1 %cmp4, label %if.then5, label %if.else
+ %i.026 = phi i32 [ %inc, %if.end.while.body_crit_edge ], [ 0, %while.body.preheader ]
+ %call3 = tail call i32 @gf1(i32 0) #4
+ %cmp4 = icmp ult i32 %call3, 10
+ %arrayidx6 = getelementptr inbounds i32, i32 addrspace(4)* %A, i32 %i.026
+ %1 = load i32, i32 addrspace(4)* %arrayidx6, align 4
+ br i1 %cmp4, label %if.then5, label %if.else
+
+if.then5:
+; CHECK: DIVERGENT: %mul = shl i32 %1, 1
+; CHECK: DIVERGENT: %2 = load i32, i32 addrspace(4)* %arrayidx10, align 4
+; CHECK: DIVERGENT: %add = add nsw i32 %2, %mul
+ %mul = shl i32 %1, 1
+ %2 = load i32, i32 addrspace(4)* %arrayidx10, align 4
+ %add = add nsw i32 %2, %mul
+ br label %if.end
+
+if.else:
+; CHECK: DIVERGENT: %mul9 = shl i32 %1, 2
+; CHECK: DIVERGENT: %3 = load i32, i32 addrspace(4)* %arrayidx10, align 4
+; CHECK: DIVERGENT: %add11 = add nsw i32 %3, %mul9
+ %mul9 = shl i32 %1, 2
+ %3 = load i32, i32 addrspace(4)* %arrayidx10, align 4
+ %add11 = add nsw i32 %3, %mul9
+ br label %if.end
+
+if.end:
+; CHECK: DIVERGENT: %storemerge = phi i32 [ %add11, %if.else ], [ %add, %if.then5 ]
+; CHECK: DIVERGENT: store i32 %storemerge, i32 addrspace(4)* %arrayidx10, align 4
+; CHECK-NOT: DIVERGENT: %inc = add nuw nsw i32 %i.026, 1
+; CHECK: DIVERGENT: %exitcond = icmp ne i32 %inc, %0
+; CHECK: DIVERGENT: br i1 %exitcond, label %if.end.while.body_crit_edge, label %while.end.loopexit
+ %storemerge = phi i32 [ %add11, %if.else ], [ %add, %if.then5 ]
+ store i32 %storemerge, i32 addrspace(4)* %arrayidx10, align 4
+ %inc = add nuw nsw i32 %i.026, 1
+ %exitcond = icmp ne i32 %inc, %0
+ br i1 %exitcond, label %if.end.while.body_crit_edge, label %while.end.loopexit
+
+if.end.while.body_crit_edge:
+ br label %while.body
+
+while.end.loopexit:
+; CHECK: DIVERGENT: %storemerge.lcssa = phi i32 [ %storemerge, %if.end ]
+ %storemerge.lcssa = phi i32 [ %storemerge, %if.end ]
+ br label %while.end
+
+while.end:
+; CHECK: DIVERGENT: %4 = phi i32 [ %.pre, %if.then.while.end_crit_edge ], [ %storemerge.lcssa, %while.end.loopexit ]
+; CHECK: DIVERGENT: %i.0.lcssa = phi i32 [ 0, %if.then.while.end_crit_edge ], [ %0, %while.end.loopexit ]
+; CHECK: DIVERGENT: %sub = sub nsw i32 %4, %i.0.lcssa
+; CHECK: DIVERGENT: store i32 %sub, i32 addrspace(4)* %arrayidx10, align 4
+ %4 = phi i32 [ %.pre, %if.then.while.end_crit_edge ], [ %storemerge.lcssa, %while.end.loopexit ]
+ %i.0.lcssa = phi i32 [ 0, %if.then.while.end_crit_edge ], [ %0, %while.end.loopexit ]
+ %sub = sub nsw i32 %4, %i.0.lcssa
+ store i32 %sub, i32 addrspace(4)* %arrayidx10, align 4
+ br label %new_exit
+
+new_exit:
+ ret void
+}
+
+attributes #0 = { nounwind readnone }
+attributes #1 = { nounwind readnone }
+attributes #2 = { nounwind readnone }
+attributes #3 = { nounwind readnone }
+attributes #4 = { nounwind readnone }
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