[llvm-commits] CVS: llvm/lib/Transforms/Scalar/LowerSwitch.cpp
Chris Lattner
lattner at cs.uiuc.edu
Tue Oct 7 13:47:01 PDT 2003
Changes in directory llvm/lib/Transforms/Scalar:
LowerSwitch.cpp updated: 1.4 -> 1.5
---
Log message:
Bill contributed this major rewrite of the -lowerswitch pass to make it generate
logarithmic conditional branch sequences instead of linear sequences. Thanks Bill!
---
Diffs of the changes: (+144 -44)
Index: llvm/lib/Transforms/Scalar/LowerSwitch.cpp
diff -u llvm/lib/Transforms/Scalar/LowerSwitch.cpp:1.4 llvm/lib/Transforms/Scalar/LowerSwitch.cpp:1.5
--- llvm/lib/Transforms/Scalar/LowerSwitch.cpp:1.4 Sat Aug 23 17:54:34 2003
+++ llvm/lib/Transforms/Scalar/LowerSwitch.cpp Tue Oct 7 13:46:23 2003
@@ -7,11 +7,13 @@
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
+#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/iTerminators.h"
#include "llvm/iOperators.h"
#include "llvm/iPHINode.h"
#include "llvm/Pass.h"
+#include "Support/Debug.h"
#include "Support/Statistic.h"
namespace {
@@ -20,9 +22,30 @@
/// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
/// instructions. Note that this cannot be a BasicBlock pass because it
/// modifies the CFG!
- struct LowerSwitch : public FunctionPass {
+ class LowerSwitch : public FunctionPass {
+ public:
bool runOnFunction(Function &F);
+ typedef std::pair<Constant*, BasicBlock*> Case;
+ typedef std::vector<Case>::iterator CaseItr;
+ private:
void processSwitchInst(SwitchInst *SI);
+
+ BasicBlock* switchConvert(CaseItr Begin, CaseItr End, Value* Val,
+ BasicBlock* OrigBlock, BasicBlock* Default);
+ BasicBlock* newLeafBlock(Case& Leaf, Value* Val,
+ BasicBlock* OrigBlock, BasicBlock* Default);
+ };
+
+ /// The comparison function for sorting the switch case values in the vector.
+ struct CaseCmp {
+ bool operator () (const LowerSwitch::Case& C1,
+ const LowerSwitch::Case& C2) {
+ if (const ConstantUInt* U1 = dyn_cast<const ConstantUInt>(C1.first))
+ return U1->getValue() < cast<const ConstantUInt>(C2.first)->getValue();
+
+ const ConstantSInt* S1 = dyn_cast<const ConstantSInt>(C1.first);
+ return S1->getValue() < cast<const ConstantSInt>(C2.first)->getValue();
+ }
};
RegisterOpt<LowerSwitch>
@@ -49,16 +72,107 @@
return Changed;
}
+// operator<< - Used for debugging purposes.
+//
+std::ostream& operator << (std::ostream& O, std::vector<LowerSwitch::Case>& C)
+{
+ O << "[";
+
+ for (std::vector<LowerSwitch::Case>::iterator B = C.begin(), E = C.end();
+ B != E; ) {
+ O << *B->first;
+ if (++B != E) O << ", ";
+ }
+
+ return 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)
+{
+ unsigned Size = End - Begin;
+
+ if (Size == 1)
+ return newLeafBlock(*Begin, Val, OrigBlock, Default);
+
+ unsigned Mid = Size / 2;
+ std::vector<Case> LHS(Begin, Begin + Mid);
+ DEBUG(std::cerr << "LHS: " << LHS << "\n");
+ std::vector<Case> RHS(Begin + Mid, End);
+ DEBUG(std::cerr << "RHS: " << RHS << "\n");
+
+ Case& Pivot = *(Begin + Mid);
+ DEBUG(std::cerr << "Pivot ==> "
+ << cast<ConstantUInt>(Pivot.first)->getValue() << "\n");
+
+ BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
+ OrigBlock, Default);
+ BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), 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.
+ Function* F = OrigBlock->getParent();
+ BasicBlock* NewNode = new BasicBlock("NodeBlock");
+ F->getBasicBlockList().insert(OrigBlock->getNext(), NewNode);
+
+ SetCondInst* Comp = new SetCondInst(Instruction::SetLT, Val, Pivot.first,
+ "Pivot");
+ NewNode->getInstList().push_back(Comp);
+ BranchInst* Br = new BranchInst(LBranch, RBranch, Comp);
+ NewNode->getInstList().push_back(Br);
+ return NewNode;
+}
+
+// newLeafBlock - Create a new leaf block for the binary lookup tree. It
+// checks if the switch's value == the case's value. If not, then it
+// jumps to the default branch. At this point in the tree, the value
+// can't be another valid case value, so the jump to the "default" branch
+// is warranted.
+//
+BasicBlock* LowerSwitch::newLeafBlock(Case& Leaf, Value* Val,
+ BasicBlock* OrigBlock,
+ BasicBlock* Default)
+{
+ Function* F = OrigBlock->getParent();
+ BasicBlock* NewLeaf = new BasicBlock("LeafBlock");
+ F->getBasicBlockList().insert(OrigBlock->getNext(), NewLeaf);
+
+ // Make the seteq instruction...
+ SetCondInst* Comp = new SetCondInst(Instruction::SetEQ, Val,
+ Leaf.first, "SwitchLeaf");
+ NewLeaf->getInstList().push_back(Comp);
+
+ // Make the conditional branch...
+ BasicBlock* Succ = Leaf.second;
+ Instruction* Br = new BranchInst(Succ, Default, Comp);
+ NewLeaf->getInstList().push_back(Br);
+
+ // If there were any PHI nodes in this successor, rewrite one entry
+ // from OrigBlock to come from NewLeaf.
+ for (BasicBlock::iterator I = Succ->begin();
+ PHINode* PN = dyn_cast<PHINode>(I); ++I) {
+ int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
+ assert(BlockIdx != -1 && "Switch didn't go to this successor??");
+ PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
+ }
+
+ return NewLeaf;
+}
+
// processSwitchInst - Replace the specified switch instruction with a sequence
-// of chained basic blocks. Right now we just insert an incredibly stupid
-// linear sequence of branches. It would be better to do a balanced binary
-// search eventually. FIXME
+// of chained if-then insts in a balanced binary search.
//
void LowerSwitch::processSwitchInst(SwitchInst *SI) {
BasicBlock *CurBlock = SI->getParent();
BasicBlock *OrigBlock = CurBlock;
Function *F = CurBlock->getParent();
Value *Val = SI->getOperand(0); // The value we are switching on...
+ BasicBlock* Default = SI->getDefaultDest();
// Unlink the switch instruction from it's block.
CurBlock->getInstList().remove(SI);
@@ -70,49 +184,35 @@
return;
}
- // Expand comparisons for all of the non-default cases...
- for (unsigned i = 2, e = SI->getNumOperands(); i != e; i += 2) {
- // Insert a new basic block after the current one...
- BasicBlock *NextBlock;
- if (i != e-2) {
- NextBlock = new BasicBlock("switchblock");
- F->getBasicBlockList().insert(CurBlock->getNext(), NextBlock);
- } else { // Last case, if it's not the value, go to default block.
- NextBlock = cast<BasicBlock>(SI->getDefaultDest());
- }
+ // 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 = new BasicBlock("NewDefault");
+ F->getBasicBlockList().insert(Default, NewDefault);
+
+ NewDefault->getInstList().push_back(new BranchInst(Default));
+
+ // 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();
+ PHINode *PN = dyn_cast<PHINode>(I); ++I) {
+ int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
+ assert(BlockIdx != -1 && "Switch didn't go to this successor??");
+ PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
+ }
- // Make the seteq instruction...
- Instruction *Comp = new SetCondInst(Instruction::SetEQ, Val,
- SI->getOperand(i), "switchcase");
- CurBlock->getInstList().push_back(Comp);
-
- // Make the conditional branch...
- BasicBlock *Succ = cast<BasicBlock>(SI->getOperand(i+1));
- Instruction *Br = new BranchInst(Succ, NextBlock, Comp);
- CurBlock->getInstList().push_back(Br);
-
- // If there were any PHI nodes in this successor, rewrite one entry from
- // OrigBlock to come from CurBlock.
- for (BasicBlock::iterator I = Succ->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++I) {
- int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
- assert(BlockIdx != -1 && "Switch didn't go to this successor??");
- PN->setIncomingBlock((unsigned)BlockIdx, CurBlock);
- }
+ std::vector<Case> Cases;
- if (i == e-2) { // Is this looking at the default destination?
- // If there is an entry in any PHI nodes for the default edge, make sure
- // to update them as well.
- for (BasicBlock::iterator I = NextBlock->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++I) {
- int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
- assert(BlockIdx != -1 && "Switch didn't go to this successor??");
- PN->setIncomingBlock((unsigned)BlockIdx, CurBlock);
- }
- }
+ // Expand comparisons for all of the non-default cases...
+ for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
+ Cases.push_back(Case(SI->getSuccessorValue(i), SI->getSuccessor(i)));
- CurBlock = NextBlock; // Move on to the next condition
- }
+ std::sort(Cases.begin(), Cases.end(), CaseCmp());
+ DEBUG(std::cerr << "Cases: " << Cases << "\n");
+ BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
+ OrigBlock, NewDefault);
+
+ // Branch to our shiny new if-then stuff...
+ OrigBlock->getInstList().push_back(new BranchInst(SwitchBlock));
// We are now done with the switch instruction, delete it.
delete SI;
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