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-rw-r--r--lib/Transforms/Utils/LowerSwitch.cpp129
1 files changed, 102 insertions, 27 deletions
diff --git a/lib/Transforms/Utils/LowerSwitch.cpp b/lib/Transforms/Utils/LowerSwitch.cpp
index 9ef694c..eac693b 100644
--- a/lib/Transforms/Utils/LowerSwitch.cpp
+++ b/lib/Transforms/Utils/LowerSwitch.cpp
@@ -14,11 +14,13 @@
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/CFG.h"
#include "llvm/Pass.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
@@ -58,16 +60,18 @@ namespace {
Low(low), High(high), BB(bb) { }
};
- typedef std::vector<CaseRange> CaseVector;
+ typedef std::vector<CaseRange> CaseVector;
typedef std::vector<CaseRange>::iterator CaseItr;
private:
void processSwitchInst(SwitchInst *SI);
- BasicBlock* switchConvert(CaseItr Begin, CaseItr End, Value* Val,
- BasicBlock* OrigBlock, BasicBlock* Default);
- BasicBlock* newLeafBlock(CaseRange& Leaf, Value* Val,
- BasicBlock* OrigBlock, BasicBlock* Default);
- unsigned Clusterify(CaseVector& Cases, SwitchInst *SI);
+ BasicBlock *switchConvert(CaseItr Begin, CaseItr End,
+ ConstantInt *LowerBound, ConstantInt *UpperBound,
+ Value *Val, BasicBlock *OrigBlock,
+ BasicBlock *Default);
+ BasicBlock *newLeafBlock(CaseRange &Leaf, Value *Val, BasicBlock *OrigBlock,
+ BasicBlock *Default);
+ unsigned Clusterify(CaseVector &Cases, SwitchInst *SI);
};
/// The comparison function for sorting the switch case values in the vector.
@@ -129,15 +133,26 @@ static raw_ostream& operator<<(raw_ostream &O,
// switchConvert - Convert the switch statement into a binary lookup of
// the case values. The function recursively builds this tree.
-//
-BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
- Value* Val, BasicBlock* OrigBlock,
- BasicBlock* Default)
-{
+// LowerBound and UpperBound are used to keep track of the bounds for Val
+// that have already been checked by a block emitted by one of the previous
+// calls to switchConvert in the call stack.
+BasicBlock *LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
+ ConstantInt *LowerBound,
+ ConstantInt *UpperBound, Value *Val,
+ BasicBlock *OrigBlock,
+ BasicBlock *Default) {
unsigned Size = End - Begin;
- if (Size == 1)
+ if (Size == 1) {
+ // Check if the Case Range is perfectly squeezed in between
+ // already checked Upper and Lower bounds. If it is then we can avoid
+ // emitting the code that checks if the value actually falls in the range
+ // because the bounds already tell us so.
+ if (Begin->Low == LowerBound && Begin->High == UpperBound) {
+ return Begin->BB;
+ }
return newLeafBlock(*Begin, Val, OrigBlock, Default);
+ }
unsigned Mid = Size / 2;
std::vector<CaseRange> LHS(Begin, Begin + Mid);
@@ -145,15 +160,50 @@ BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
std::vector<CaseRange> RHS(Begin + Mid, End);
DEBUG(dbgs() << "RHS: " << RHS << "\n");
- CaseRange& Pivot = *(Begin + Mid);
- DEBUG(dbgs() << "Pivot ==> "
- << cast<ConstantInt>(Pivot.Low)->getValue() << " -"
- << cast<ConstantInt>(Pivot.High)->getValue() << "\n");
+ CaseRange &Pivot = *(Begin + Mid);
+ DEBUG(dbgs() << "Pivot ==> "
+ << cast<ConstantInt>(Pivot.Low)->getValue()
+ << " -" << cast<ConstantInt>(Pivot.High)->getValue() << "\n");
+
+ // NewLowerBound here should never be the integer minimal value.
+ // This is because it is computed from a case range that is never
+ // the smallest, so there is always a case range that has at least
+ // a smaller value.
+ ConstantInt *NewLowerBound = cast<ConstantInt>(Pivot.Low);
+ ConstantInt *NewUpperBound;
+
+ // If we don't have a Default block then it means that we can never
+ // have a value outside of a case range, so set the UpperBound to the highest
+ // value in the LHS part of the case ranges.
+ if (Default != nullptr) {
+ // Because NewLowerBound is never the smallest representable integer
+ // it is safe here to subtract one.
+ NewUpperBound = ConstantInt::get(NewLowerBound->getContext(),
+ NewLowerBound->getValue() - 1);
+ } else {
+ CaseItr LastLHS = LHS.begin() + LHS.size() - 1;
+ NewUpperBound = cast<ConstantInt>(LastLHS->High);
+ }
- BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
- OrigBlock, Default);
- BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), Val,
- OrigBlock, Default);
+ DEBUG(dbgs() << "LHS Bounds ==> ";
+ if (LowerBound) {
+ dbgs() << cast<ConstantInt>(LowerBound)->getSExtValue();
+ } else {
+ dbgs() << "NONE";
+ }
+ dbgs() << " - " << NewUpperBound->getSExtValue() << "\n";
+ dbgs() << "RHS Bounds ==> ";
+ dbgs() << NewLowerBound->getSExtValue() << " - ";
+ if (UpperBound) {
+ dbgs() << cast<ConstantInt>(UpperBound)->getSExtValue() << "\n";
+ } else {
+ dbgs() << "NONE\n";
+ });
+
+ BasicBlock *LBranch = switchConvert(LHS.begin(), LHS.end(), LowerBound,
+ NewUpperBound, Val, OrigBlock, Default);
+ BasicBlock *RBranch = switchConvert(RHS.begin(), RHS.end(), NewLowerBound,
+ UpperBound, Val, OrigBlock, Default);
// Create a new node that checks if the value is < pivot. Go to the
// left branch if it is and right branch if not.
@@ -291,13 +341,19 @@ void LowerSwitch::processSwitchInst(SwitchInst *SI) {
return;
}
+ const bool DefaultIsUnreachable =
+ Default->size() == 1 && isa<UnreachableInst>(Default->getTerminator());
// Create a new, empty default block so that the new hierarchy of
// if-then statements go to this and the PHI nodes are happy.
- BasicBlock* NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
- F->getBasicBlockList().insert(Default, NewDefault);
-
- BranchInst::Create(Default, NewDefault);
-
+ // if the default block is set as an unreachable we avoid creating one
+ // because will never be a valid target.
+ BasicBlock *NewDefault = nullptr;
+ if (!DefaultIsUnreachable) {
+ NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
+ F->getBasicBlockList().insert(Default, NewDefault);
+
+ BranchInst::Create(Default, NewDefault);
+ }
// If there is an entry in any PHI nodes for the default edge, make sure
// to update them as well.
for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
@@ -316,12 +372,31 @@ void LowerSwitch::processSwitchInst(SwitchInst *SI) {
DEBUG(dbgs() << "Cases: " << Cases << "\n");
(void)numCmps;
- BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
- OrigBlock, NewDefault);
+ ConstantInt *UpperBound = nullptr;
+ ConstantInt *LowerBound = nullptr;
+
+ // Optimize the condition where Default is an unreachable block. In this case
+ // we can make the bounds tightly fitted around the case value ranges,
+ // because we know that the value passed to the switch should always be
+ // exactly one of the case values.
+ if (DefaultIsUnreachable) {
+ CaseItr LastCase = Cases.begin() + Cases.size() - 1;
+ UpperBound = cast<ConstantInt>(LastCase->High);
+ LowerBound = cast<ConstantInt>(Cases.begin()->Low);
+ }
+ BasicBlock *SwitchBlock =
+ switchConvert(Cases.begin(), Cases.end(), LowerBound, UpperBound, Val,
+ OrigBlock, NewDefault);
// Branch to our shiny new if-then stuff...
BranchInst::Create(SwitchBlock, OrigBlock);
// We are now done with the switch instruction, delete it.
CurBlock->getInstList().erase(SI);
+
+ pred_iterator PI = pred_begin(Default), E = pred_end(Default);
+ // If the Default block has no more predecessors just remove it
+ if (PI == E) {
+ DeleteDeadBlock(Default);
+ }
}
generated by cgit v1.1 at 2024-09-22 16:17:27 +0000