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[DivergenceAnalysis] fix a bug in computing influence regions 

Fixes PR25864

llvm-svn: 256036
This commit is contained in:
Jingyue Wu 2015-12-18 21:44:26 +00:00
parent ba3ca76ed2
commit 3f422280f5
2 changed files with 41 additions and 8 deletions
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26
llvm/lib/Analysis/DivergenceAnalysis.cpp
View File

@ -96,7 +96,7 @@ private:
// A helper function that explores sync dependents of TI.
void exploreSyncDependency(TerminatorInst *TI);
// Computes the influence region from Start to End. This region includes all
// basic blocks on any path from Start to End.
// basic blocks on any simple path from Start to End.
void computeInfluenceRegion(BasicBlock *Start, BasicBlock *End,
DenseSet<BasicBlock *> &InfluenceRegion);
// Finds all users of I that are outside the influence region, and add these
@ -198,21 +198,33 @@ void DivergencePropagator::findUsersOutsideInfluenceRegion(
}
}
// A helper function for computeInfluenceRegion that adds successors of "ThisBB"
// to the influence region.
static void
addSuccessorsToInfluenceRegion(BasicBlock *ThisBB, BasicBlock *End,
DenseSet<BasicBlock *> &InfluenceRegion,
std::vector<BasicBlock *> &InfluenceStack) {
for (BasicBlock *Succ : successors(ThisBB)) {
if (Succ != End && InfluenceRegion.insert(Succ).second)
InfluenceStack.push_back(Succ);
}
}
void DivergencePropagator::computeInfluenceRegion(
BasicBlock *Start, BasicBlock *End,
DenseSet<BasicBlock *> &InfluenceRegion) {
assert(PDT.properlyDominates(End, Start) &&
"End does not properly dominate Start");
// The influence region starts from the end of "Start" to the beginning of
// "End". Therefore, "Start" should not be in the region unless "Start" is in
// a loop that doesn't contain "End".
std::vector<BasicBlock *> InfluenceStack;
InfluenceStack.push_back(Start);
InfluenceRegion.insert(Start);
addSuccessorsToInfluenceRegion(Start, End, InfluenceRegion, InfluenceStack);
while (!InfluenceStack.empty()) {
BasicBlock *BB = InfluenceStack.back();
InfluenceStack.pop_back();
for (BasicBlock *Succ : successors(BB)) {
if (End != Succ && InfluenceRegion.insert(Succ).second)
InfluenceStack.push_back(Succ);
}
addSuccessorsToInfluenceRegion(BB, End, InfluenceRegion, InfluenceStack);
}
}

23
llvm/test/Analysis/DivergenceAnalysis/NVPTX/diverge.ll
View File

@ -185,14 +185,35 @@ else:
ret i32 1
}
; Verifies sync-dependence is computed correctly in the absense of loops.
define i32 @sync_no_loop(i32 %arg) {
entry:
%0 = add i32 %arg, 1
%tid = call i32 @llvm.nvvm.read.ptx.sreg.tid.x()
%1 = icmp sge i32 %tid, 10
br i1 %1, label %bb1, label %bb2
bb1:
br label %bb3
bb2:
br label %bb3
bb3:
%2 = add i32 %0, 2
; CHECK-NOT: DIVERGENT: %2
ret i32 %2
}
declare i32 @llvm.nvvm.read.ptx.sreg.tid.x()
declare i32 @llvm.nvvm.read.ptx.sreg.tid.y()
declare i32 @llvm.nvvm.read.ptx.sreg.tid.z()
declare i32 @llvm.ptx.read.laneid()
!nvvm.annotations = !{!0, !1, !2, !3, !4}
!nvvm.annotations = !{!0, !1, !2, !3, !4, !5}
!0 = !{i32 (i32, i32, i32)* @no_diverge, !"kernel", i32 1}
!1 = !{i32 (i32, i32)* @sync, !"kernel", i32 1}
!2 = !{i32 (i32, i32, i32)* @mixed, !"kernel", i32 1}
!3 = !{i32 ()* @loop, !"kernel", i32 1}
!4 = !{i32 (i1)* @unstructured_loop, !"kernel", i32 1}
!5 = !{i32 (i32)* @sync_no_loop, !"kernel", i32 1}