diff options
| -rw-r--r-- | lib/Transforms/Utils/SimplifyCFG.cpp | 27 | ||||
| -rw-r--r-- | test/Transforms/SimplifyCFG/SpeculativeExec.ll | 29 |
2 files changed, 47 insertions, 9 deletions
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp index 11cb25d0f9..9f3464de43 100644 --- a/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/lib/Transforms/Utils/SimplifyCFG.cpp @@ -1369,7 +1369,8 @@ static bool SinkThenElseCodeToEnd(BranchInst *BI1) { /// \endcode /// /// \returns true if the conditional block is removed. -static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) { +static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB, + const TargetTransformInfo &TTI) { // Be conservative for now. FP select instruction can often be expensive. Value *BrCond = BI->getCondition(); if (isa<FCmpInst>(BrCond)) @@ -1398,15 +1399,22 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) { // Only speculatively execution a single instruction (not counting the // terminator) for now. - ++SpeculationCost; - if (SpeculationCost > 1) + SpeculationCost += TTI.getUserCost(I); + if (SpeculationCost > TargetTransformInfo::TCC_Basic) return false; // Don't hoist the instruction if it's unsafe or expensive. if (!isSafeToSpeculativelyExecute(I)) return false; - if (ComputeSpeculationCost(I) > PHINodeFoldingThreshold) + // FIXME: This should really be a cost metric, but our cost model doesn't + // accurately model the expense of select. + if (isa<SelectInst>(I)) return false; + // FIXME: The cost metric currently doesn't reason accurately about simple + // versus complex GEPs, take a conservative approach here. + if (GEPOperator *GEP = dyn_cast<GEPOperator>(I)) + if (!GEP->hasAllConstantIndices()) + return false; // Do not hoist the instruction if any of its operands are defined but not // used in this BB. The transformation will prevent the operand from @@ -1449,9 +1457,10 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) { // Account for the cost of an unfolded ConstantExpr which could end up // getting expanded into Instructions. // FIXME: This doesn't account for how many operations are combined in the - // constant expression. - ++SpeculationCost; - if (SpeculationCost > 1) + // constant expression. The cost functions in TTI don't yet correctly model + // constant expression costs. + SpeculationCost += TargetTransformInfo::TCC_Basic; + if (SpeculationCost > TargetTransformInfo::TCC_Basic) return false; } @@ -3868,7 +3877,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) { TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator(); if (Succ0TI->getNumSuccessors() == 1 && Succ0TI->getSuccessor(0) == BI->getSuccessor(1)) - if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0))) + if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), TTI)) return SimplifyCFG(BB, TTI, TD) | true; } } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { @@ -3877,7 +3886,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) { TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator(); if (Succ1TI->getNumSuccessors() == 1 && Succ1TI->getSuccessor(0) == BI->getSuccessor(0)) - if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1))) + if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), TTI)) return SimplifyCFG(BB, TTI, TD) | true; } diff --git a/test/Transforms/SimplifyCFG/SpeculativeExec.ll b/test/Transforms/SimplifyCFG/SpeculativeExec.ll index 7e27f415f7..bcef848040 100644 --- a/test/Transforms/SimplifyCFG/SpeculativeExec.ll +++ b/test/Transforms/SimplifyCFG/SpeculativeExec.ll @@ -108,3 +108,32 @@ end: ret i8* %x10 } + +define i16 @test5(i1* %dummy, i16 %a, i16 %b) { +; Test that we speculate no-op instructions. +; CHECK: @test5 + +entry: + %cond1 = load volatile i1* %dummy + br i1 %cond1, label %if, label %end + +if: + %cond2 = load volatile i1* %dummy + %a.conv = sext i16 %a to i32 + %b.conv = sext i16 %b to i32 + %cmp = icmp ult i32 %a.conv, %b.conv + br i1 %cond2, label %then, label %end + +then: + %sub = sub i32 %a.conv, %b.conv + %sub.conv = trunc i32 %sub to i16 + br label %end + +end: + %x = phi i16 [ %a, %entry ], [ %b, %if ], [ %sub.conv, %then ] +; CHECK-NOT: phi +; CHECK: select i1 + + ret i16 %x +} + |