[SimplifyCFG] Pass context instruction to isSafeToSpeculativelyExecute() (#109132)
Pass speculation target and assumption cache to isSafeToSpeculativelyExecute() calls. This allows speculating based on dereferenceable/align assumptions, but the primary motivation here is to avoid regressions from planned changes to fix https://github.com/llvm/llvm-project/issues/108854.
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Nikita Popov
GitHub
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752e10379c
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30cdf1e959
@ -398,9 +398,6 @@ static void addPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
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/// expensive.
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static InstructionCost computeSpeculationCost(const User *I,
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const TargetTransformInfo &TTI) {
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assert((!isa<Instruction>(I) ||
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isSafeToSpeculativelyExecute(cast<Instruction>(I))) &&
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"Instruction is not safe to speculatively execute!");
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return TTI.getInstructionCost(I, TargetTransformInfo::TCK_SizeAndLatency);
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}
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@ -421,12 +418,11 @@ static InstructionCost computeSpeculationCost(const User *I,
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/// After this function returns, Cost is increased by the cost of
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/// V plus its non-dominating operands. If that cost is greater than
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/// Budget, false is returned and Cost is undefined.
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static bool dominatesMergePoint(Value *V, BasicBlock *BB,
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static bool dominatesMergePoint(Value *V, BasicBlock *BB, Instruction *InsertPt,
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SmallPtrSetImpl<Instruction *> &AggressiveInsts,
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InstructionCost &Cost,
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InstructionCost Budget,
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InstructionCost &Cost, InstructionCost Budget,
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const TargetTransformInfo &TTI,
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unsigned Depth = 0) {
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AssumptionCache *AC, unsigned Depth = 0) {
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// It is possible to hit a zero-cost cycle (phi/gep instructions for example),
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// so limit the recursion depth.
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// TODO: While this recursion limit does prevent pathological behavior, it
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@ -461,7 +457,7 @@ static bool dominatesMergePoint(Value *V, BasicBlock *BB,
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// Okay, it looks like the instruction IS in the "condition". Check to
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// see if it's a cheap instruction to unconditionally compute, and if it
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// only uses stuff defined outside of the condition. If so, hoist it out.
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if (!isSafeToSpeculativelyExecute(I))
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if (!isSafeToSpeculativelyExecute(I, InsertPt, AC))
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return false;
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Cost += computeSpeculationCost(I, TTI);
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@ -480,8 +476,8 @@ static bool dominatesMergePoint(Value *V, BasicBlock *BB,
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// Okay, we can only really hoist these out if their operands do
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// not take us over the cost threshold.
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for (Use &Op : I->operands())
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if (!dominatesMergePoint(Op, BB, AggressiveInsts, Cost, Budget, TTI,
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Depth + 1))
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if (!dominatesMergePoint(Op, BB, InsertPt, AggressiveInsts, Cost, Budget,
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TTI, AC, Depth + 1))
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return false;
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// Okay, it's safe to do this! Remember this instruction.
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AggressiveInsts.insert(I);
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@ -3140,7 +3136,8 @@ bool SimplifyCFGOpt::speculativelyExecuteBB(BranchInst *BI,
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return false;
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// Don't hoist the instruction if it's unsafe or expensive.
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if (!IsSafeCheapLoadStore && !isSafeToSpeculativelyExecute(&I) &&
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if (!IsSafeCheapLoadStore &&
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!isSafeToSpeculativelyExecute(&I, BI, Options.AC) &&
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!(HoistCondStores && !SpeculatedStoreValue &&
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(SpeculatedStoreValue =
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isSafeToSpeculateStore(&I, BB, ThenBB, EndBB))))
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@ -3651,7 +3648,8 @@ static bool foldCondBranchOnValueKnownInPredecessor(BranchInst *BI,
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/// Given a BB that starts with the specified two-entry PHI node,
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/// see if we can eliminate it.
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static bool foldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
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DomTreeUpdater *DTU, const DataLayout &DL,
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DomTreeUpdater *DTU, AssumptionCache *AC,
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const DataLayout &DL,
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bool SpeculateUnpredictables) {
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// Ok, this is a two entry PHI node. Check to see if this is a simple "if
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// statement", which has a very simple dominance structure. Basically, we
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@ -3741,10 +3739,10 @@ static bool foldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
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continue;
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}
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if (!dominatesMergePoint(PN->getIncomingValue(0), BB, AggressiveInsts,
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Cost, Budget, TTI) ||
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!dominatesMergePoint(PN->getIncomingValue(1), BB, AggressiveInsts,
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Cost, Budget, TTI))
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if (!dominatesMergePoint(PN->getIncomingValue(0), BB, DomBI,
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AggressiveInsts, Cost, Budget, TTI, AC) ||
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!dominatesMergePoint(PN->getIncomingValue(1), BB, DomBI,
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AggressiveInsts, Cost, Budget, TTI, AC))
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return Changed;
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}
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@ -8116,7 +8114,7 @@ bool SimplifyCFGOpt::simplifyOnce(BasicBlock *BB) {
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// eliminate it, do so now.
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if (auto *PN = dyn_cast<PHINode>(BB->begin()))
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if (PN->getNumIncomingValues() == 2)
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if (foldTwoEntryPHINode(PN, TTI, DTU, DL,
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if (foldTwoEntryPHINode(PN, TTI, DTU, Options.AC, DL,
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Options.SpeculateUnpredictables))
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return true;
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}
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@ -4,14 +4,10 @@
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define i64 @align_deref_align(i1 %c, ptr %p) {
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; CHECK-LABEL: define i64 @align_deref_align(
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; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*]]:
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ]
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; CHECK-NEXT: br i1 [[C]], label %[[IF:.*]], label %[[EXIT:.*]]
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; CHECK: [[IF]]:
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; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8
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; CHECK-NEXT: br label %[[EXIT]]
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; CHECK: [[EXIT]]:
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; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[V]], %[[IF]] ], [ 0, %[[ENTRY]] ]
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; CHECK-NEXT: [[RES:%.*]] = select i1 [[C]], i64 [[V]], i64 0
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; CHECK-NEXT: ret i64 [[RES]]
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;
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entry:
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@ -30,17 +26,12 @@ exit:
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define i64 @assume_deref_align2(i1 %c1, i32 %x, ptr %p) {
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; CHECK-LABEL: define i64 @assume_deref_align2(
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; CHECK-SAME: i1 [[C1:%.*]], i32 [[X:%.*]], ptr [[P:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*]]:
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ]
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; CHECK-NEXT: br i1 [[C1]], label %[[IF1:.*]], label %[[EXIT:.*]]
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; CHECK: [[IF1]]:
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; CHECK-NEXT: [[C2:%.*]] = icmp ugt i32 [[X]], 10
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; CHECK-NEXT: br i1 [[C2]], label %[[IF2:.*]], label %[[EXIT]]
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; CHECK: [[IF2]]:
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; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8
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; CHECK-NEXT: br label %[[EXIT]]
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; CHECK: [[EXIT]]:
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; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[V]], %[[IF2]] ], [ 1, %[[IF1]] ], [ 0, %[[ENTRY]] ]
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; CHECK-NEXT: [[SPEC_SELECT:%.*]] = select i1 [[C2]], i64 [[V]], i64 1
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; CHECK-NEXT: [[RES:%.*]] = select i1 [[C1]], i64 [[SPEC_SELECT]], i64 0
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; CHECK-NEXT: ret i64 [[RES]]
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;
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entry:
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