From 448da519cca87cbcba620188e1e595dc1f120512 Mon Sep 17 00:00:00 2001 From: Hans Wennborg Date: Sat, 18 Jun 2011 10:28:47 +0000 Subject: [PATCH] Fix PR10103: Less code for enum type translation. In cases such as the attached test, where the case value for a switch destination is used in a phi node that follows the destination, it might be better to replace that value with the condition value of the switch, so that more blocks can be folded away with TryToSimplifyUncondBranchFromEmptyBlock because there are less conflicts in the phi node. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133344 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Utils/SimplifyCFG.cpp | 74 +++++++++++++++++++ .../ForwardSwitchConditionToPHI.ll | 36 +++++++++ .../SimplifyCFG/switch_switch_fold_dbginfo.ll | 2 +- 3 files changed, 111 insertions(+), 1 deletion(-) create mode 100644 test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp index 6df846cbd18..7b93b4a8e25 100644 --- a/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/lib/Transforms/Utils/SimplifyCFG.cpp @@ -2450,6 +2450,77 @@ static bool EliminateDeadSwitchCases(SwitchInst *SI) { return !DeadCases.empty(); } +/// FindPHIForConditionForwarding - If BB would be eligible for simplification +/// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated +/// by an unconditional branch), look at the phi node for BB in the successor +/// block and see if the incoming value is equal to CaseValue. If so, return +/// the phi node, and set PhiIndex to BB's index in the phi node. +static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue, + BasicBlock *BB, + int *PhiIndex) { + if (BB->getFirstNonPHIOrDbg() != BB->getTerminator()) + return NULL; // BB must be empty to be a candidate for simplification. + if (!BB->getSinglePredecessor()) + return NULL; // BB must be dominated by the switch. + + BranchInst *Branch = dyn_cast(BB->getTerminator()); + if (!Branch || !Branch->isUnconditional()) + return NULL; // Terminator must be unconditional branch. + + BasicBlock *Succ = Branch->getSuccessor(0); + + BasicBlock::iterator I = Succ->begin(); + while (PHINode *PHI = dyn_cast(I++)) { + int Idx = PHI->getBasicBlockIndex(BB); + assert(Idx >= 0 && "PHI has no entry for predecessor?"); + + Value *InValue = PHI->getIncomingValue(Idx); + if (InValue != CaseValue) continue; + + *PhiIndex = Idx; + return PHI; + } + + return NULL; +} + +/// ForwardSwitchConditionToPHI - Try to forward the condition of a switch +/// instruction to a phi node dominated by the switch, if that would mean that +/// some of the destination blocks of the switch can be folded away. +/// Returns true if a change is made. +static bool ForwardSwitchConditionToPHI(SwitchInst *SI) { + typedef DenseMap > ForwardingNodesMap; + ForwardingNodesMap ForwardingNodes; + + for (unsigned I = 1; I < SI->getNumCases(); ++I) { // 0 is the default case. + ConstantInt *CaseValue = SI->getCaseValue(I); + BasicBlock *CaseDest = SI->getSuccessor(I); + + int PhiIndex; + PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest, + &PhiIndex); + if (!PHI) continue; + + ForwardingNodes[PHI].push_back(PhiIndex); + } + + bool Changed = false; + + for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(), + E = ForwardingNodes.end(); I != E; ++I) { + PHINode *Phi = I->first; + SmallVector &Indexes = I->second; + + if (Indexes.size() < 2) continue; + + for (size_t I = 0, E = Indexes.size(); I != E; ++I) + Phi->setIncomingValue(Indexes[I], SI->getCondition()); + Changed = true; + } + + return Changed; +} + bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) { // If this switch is too complex to want to look at, ignore it. if (!isValueEqualityComparison(SI)) @@ -2486,6 +2557,9 @@ bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) { if (EliminateDeadSwitchCases(SI)) return SimplifyCFG(BB) | true; + if (ForwardSwitchConditionToPHI(SI)) + return SimplifyCFG(BB) | true; + return false; } diff --git a/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll b/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll new file mode 100644 index 00000000000..1b70c065ba3 --- /dev/null +++ b/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll @@ -0,0 +1,36 @@ +; RUN: opt < %s -simplifycfg -S | \ +; RUN: not grep " switch" +; PR10131 + +; ModuleID = '' +target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32" +target triple = "i386-pc-linux-gnu" + +define i32 @t(i32 %m) nounwind readnone { +entry: + switch i32 %m, label %sw.bb4 [ + i32 0, label %sw.bb0 + i32 1, label %sw.bb1 + i32 2, label %sw.bb2 + i32 3, label %sw.bb3 + ] + +sw.bb0: ; preds = %entry + br label %return + +sw.bb1: ; preds = %entry + br label %return + +sw.bb2: ; preds = %entry + br label %return + +sw.bb3: ; preds = %entry + br label %return + +sw.bb4: ; preds = %entry + br label %return + +return: ; preds = %entry, %sw.bb4, %sw.bb3, %sw.bb2, %sw.bb1 + %retval.0 = phi i32 [ 4, %sw.bb4 ], [ 3, %sw.bb3 ], [ 2, %sw.bb2 ], [ 1, %sw.bb1 ], [ 0, %sw.bb0 ] + ret i32 %retval.0 +} diff --git a/test/Transforms/SimplifyCFG/switch_switch_fold_dbginfo.ll b/test/Transforms/SimplifyCFG/switch_switch_fold_dbginfo.ll index 7d7391af1b9..343e169edc2 100644 --- a/test/Transforms/SimplifyCFG/switch_switch_fold_dbginfo.ll +++ b/test/Transforms/SimplifyCFG/switch_switch_fold_dbginfo.ll @@ -1,5 +1,5 @@ ; RUN: opt < %s -simplifycfg -S | \ -; RUN: grep switch | count 1 +; RUN: not grep " switch" ; ModuleID = '' target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"