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Revert "[SimplifyCFG] Skip threading if the target may have divergent branches" #100994

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Merged
merged 1 commit into from
Jul 29, 2024
Merged

Revert "[SimplifyCFG] Skip threading if the target may have divergent branches" #100994

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27 changes: 12 additions & 15 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3246,12 +3246,7 @@ bool SimplifyCFGOpt::SpeculativelyExecuteBB(BranchInst *BI,
}

/// Return true if we can thread a branch across this block.
static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB,
const TargetTransformInfo &TTI) {
// Skip threading if the branch may be divergent.
if (TTI.hasBranchDivergence(BB->getParent()))
return false;

static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
int Size = 0;
EphemeralValueTracker EphTracker;

Expand Down Expand Up @@ -3306,9 +3301,10 @@ static ConstantInt *getKnownValueOnEdge(Value *V, BasicBlock *From,
/// If we have a conditional branch on something for which we know the constant
/// value in predecessors (e.g. a phi node in the current block), thread edges
/// from the predecessor to their ultimate destination.
static std::optional<bool> FoldCondBranchOnValueKnownInPredecessorImpl(
BranchInst *BI, DomTreeUpdater *DTU, const DataLayout &DL,
const TargetTransformInfo &TTI, AssumptionCache *AC) {
static std::optional<bool>
FoldCondBranchOnValueKnownInPredecessorImpl(BranchInst *BI, DomTreeUpdater *DTU,
const DataLayout &DL,
AssumptionCache *AC) {
SmallMapVector<ConstantInt *, SmallSetVector<BasicBlock *, 2>, 2> KnownValues;
BasicBlock *BB = BI->getParent();
Value *Cond = BI->getCondition();
Expand Down Expand Up @@ -3336,7 +3332,7 @@ static std::optional<bool> FoldCondBranchOnValueKnownInPredecessorImpl(
// Now we know that this block has multiple preds and two succs.
// Check that the block is small enough and values defined in the block are
// not used outside of it.
if (!BlockIsSimpleEnoughToThreadThrough(BB, TTI))
if (!BlockIsSimpleEnoughToThreadThrough(BB))
return false;

for (const auto &Pair : KnownValues) {
Expand Down Expand Up @@ -3463,14 +3459,15 @@ static std::optional<bool> FoldCondBranchOnValueKnownInPredecessorImpl(
return false;
}

static bool FoldCondBranchOnValueKnownInPredecessor(
BranchInst *BI, DomTreeUpdater *DTU, const DataLayout &DL,
const TargetTransformInfo &TTI, AssumptionCache *AC) {
static bool FoldCondBranchOnValueKnownInPredecessor(BranchInst *BI,
DomTreeUpdater *DTU,
const DataLayout &DL,
AssumptionCache *AC) {
std::optional<bool> Result;
bool EverChanged = false;
do {
// Note that None means "we changed things, but recurse further."
Result = FoldCondBranchOnValueKnownInPredecessorImpl(BI, DTU, DL, TTI, AC);
Result = FoldCondBranchOnValueKnownInPredecessorImpl(BI, DTU, DL, AC);
EverChanged |= Result == std::nullopt || *Result;
} while (Result == std::nullopt);
return EverChanged;
Expand Down Expand Up @@ -7546,7 +7543,7 @@ bool SimplifyCFGOpt::simplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
// If this is a branch on something for which we know the constant value in
// predecessors (e.g. a phi node in the current block), thread control
// through this block.
if (FoldCondBranchOnValueKnownInPredecessor(BI, DTU, DL, TTI, Options.AC))
if (FoldCondBranchOnValueKnownInPredecessor(BI, DTU, DL, Options.AC))
return requestResimplify();

// Scan predecessor blocks for conditional branches.
Expand Down
44 changes: 0 additions & 44 deletions llvm/test/Transforms/SimplifyCFG/AMDGPU/skip-threading.ll
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39 changes: 0 additions & 39 deletions llvm/test/Transforms/SimplifyCFG/convergent.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -4,9 +4,6 @@
; RUN: opt -S -passes='simplifycfg<hoist-common-insts;sink-common-insts>' < %s | FileCheck -check-prefixes=CHECK,SINK %s

declare void @foo() convergent
declare void @bar1()
declare void @bar2()
declare void @bar3()
declare i32 @tid()
declare i32 @mbcnt(i32 %a, i32 %b) convergent
declare i32 @bpermute(i32 %a, i32 %b) convergent
Expand Down Expand Up @@ -48,42 +45,6 @@ exit:
ret i32 %a
}

define i32 @test_01a(i32 %a) {
; CHECK-LABEL: @test_01a(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 [[A:%.*]], 0
; CHECK-NEXT: br i1 [[COND]], label [[EXIT_CRITEDGE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.false:
; CHECK-NEXT: call void @bar1()
; CHECK-NEXT: call void @bar2()
; CHECK-NEXT: call void @bar3()
; CHECK-NEXT: br label [[EXIT:%.*]]
; CHECK: exit.critedge:
; CHECK-NEXT: call void @bar2()
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret i32 [[A]]
;
entry:
%cond = icmp eq i32 %a, 0
br i1 %cond, label %merge, label %if.false

if.false:
call void @bar1()
br label %merge

merge:
call void @bar2()
br i1 %cond, label %exit, label %if.false.2

if.false.2:
call void @bar3()
br label %exit

exit:
ret i32 %a
}

define void @test_02(ptr %y.coerce) convergent {
; NOSINK-LABEL: @test_02(
; NOSINK-NEXT: entry:
Expand Down
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