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Implement: test/Regression/Transforms/SimplifyCFG/switch_create.ll 

This turns code like this:
  if (X == 4 | X == 7)
and
  if (X != 4 & X != 7)
into switch instructions.

llvm-svn: 11792
This commit is contained in:
Chris Lattner 2004-02-24 05:38:11 +00:00
parent ae509325d6
commit 6f4b45acf5
1 changed files with 140 additions and 7 deletions
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147
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -14,17 +14,18 @@
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/Support/CFG.h"
#include <algorithm>
#include <functional>
using namespace llvm;
// PropagatePredecessors - This gets "Succ" ready to have the predecessors from
// "BB". This is a little tricky because "Succ" has PHI nodes, which need to
// have extra slots added to them to hold the merge edges from BB's
// predecessors, and BB itself might have had PHI nodes in it. This function
// returns true (failure) if the Succ BB already has a predecessor that is a
// predecessor of BB and incoming PHI arguments would not be discernible.
// PropagatePredecessorsForPHIs - This gets "Succ" ready to have the
// predecessors from "BB". This is a little tricky because "Succ" has PHI
// nodes, which need to have extra slots added to them to hold the merge edges
// from BB's predecessors, and BB itself might have had PHI nodes in it. This
// function returns true (failure) if the Succ BB already has a predecessor that
// is a predecessor of BB and incoming PHI arguments would not be discernible.
//
// Assumption: Succ is the single successor for BB.
//
@ -200,6 +201,91 @@ static bool DominatesMergePoint(Value *V, BasicBlock *BB) {
return true;
}
// GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq
// instructions that compare a value against a constant, return the value being
// compared, and stick the constant into the Values vector.
static Value *GatherConstantSetEQs(Value *V, std::vector<Constant*> &Values) {
if (Instruction *Inst = dyn_cast<Instruction>(V))
if (Inst->getOpcode() == Instruction::SetEQ) {
if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) {
Values.push_back(C);
return Inst->getOperand(0);
} else if (Constant *C = dyn_cast<Constant>(Inst->getOperand(0))) {
Values.push_back(C);
return Inst->getOperand(1);
}
} else if (Inst->getOpcode() == Instruction::Or) {
if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
if (LHS == RHS)
return LHS;
}
return 0;
}
// GatherConstantSetNEs - Given a potentially 'and'd together collection of
// setne instructions that compare a value against a constant, return the value
// being compared, and stick the constant into the Values vector.
static Value *GatherConstantSetNEs(Value *V, std::vector<Constant*> &Values) {
if (Instruction *Inst = dyn_cast<Instruction>(V))
if (Inst->getOpcode() == Instruction::SetNE) {
if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) {
Values.push_back(C);
return Inst->getOperand(0);
} else if (Constant *C = dyn_cast<Constant>(Inst->getOperand(0))) {
Values.push_back(C);
return Inst->getOperand(1);
}
} else if (Inst->getOpcode() == Instruction::Cast) {
// Cast of X to bool is really a comparison against zero.
assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!");
Values.push_back(Constant::getNullValue(Inst->getOperand(0)->getType()));
return Inst->getOperand(0);
} else if (Inst->getOpcode() == Instruction::And) {
if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
if (LHS == RHS)
return LHS;
}
return 0;
}
/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
/// bunch of comparisons of one value against constants, return the value and
/// the constants being compared.
static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
std::vector<Constant*> &Values) {
if (Cond->getOpcode() == Instruction::Or) {
CompVal = GatherConstantSetEQs(Cond, Values);
// Return true to indicate that the condition is true if the CompVal is
// equal to one of the constants.
return true;
} else if (Cond->getOpcode() == Instruction::And) {
CompVal = GatherConstantSetNEs(Cond, Values);
// Return false to indicate that the condition is false if the CompVal is
// equal to one of the constants.
return false;
}
return false;
}
/// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
/// has no side effects, nuke it. If it uses any instructions that become dead
/// because the instruction is now gone, nuke them too.
static void ErasePossiblyDeadInstructionTree(Instruction *I) {
if (isInstructionTriviallyDead(I)) {
std::vector<Value*> Operands(I->op_begin(), I->op_end());
I->getParent()->getInstList().erase(I);
for (unsigned i = 0, e = Operands.size(); i != e; ++i)
if (Instruction *OpI = dyn_cast<Instruction>(Operands[i]))
ErasePossiblyDeadInstructionTree(OpI);
}
}
// SimplifyCFG - This function is used to do simplification of a CFG. For
// example, it adjusts branches to branches to eliminate the extra hop, it
// eliminates unreachable basic blocks, and does other "peephole" optimization
@ -389,7 +475,6 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
}
}
// Merge basic blocks into their predecessor if there is only one distinct
// pred, and if there is only one distinct successor of the predecessor, and
// if there are no PHI nodes.
@ -452,6 +537,54 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
return true;
}
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
// Change br (X == 0 | X == 1), T, F into a switch instruction.
if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
Instruction *Cond = cast<Instruction>(BI->getCondition());
// If this is a bunch of seteq's or'd together, or if it's a bunch of
// 'setne's and'ed together, collect them.
Value *CompVal = 0;
std::vector<Constant*> Values;
bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
if (CompVal && CompVal->getType()->isInteger()) {
// There might be duplicate constants in the list, which the switch
// instruction can't handle, remove them now.
std::sort(Values.begin(), Values.end());
Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
// Figure out which block is which destination.
BasicBlock *DefaultBB = BI->getSuccessor(1);
BasicBlock *EdgeBB = BI->getSuccessor(0);
if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
// Create the new switch instruction now.
SwitchInst *New = new SwitchInst(CompVal, DefaultBB, BI);
// Add all of the 'cases' to the switch instruction.
for (unsigned i = 0, e = Values.size(); i != e; ++i)
New->addCase(Values[i], EdgeBB);
// We added edges from PI to the EdgeBB. As such, if there were any
// PHI nodes in EdgeBB, they need entries to be added corresponding to
// the number of edges added.
for (BasicBlock::iterator BBI = EdgeBB->begin();
PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) {
Value *InVal = PN->getIncomingValueForBlock(*PI);
for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
PN->addIncoming(InVal, *PI);
}
// Erase the old branch instruction.
(*PI)->getInstList().erase(BI);
// Erase the potentially condition tree that was used to computed the
// branch condition.
ErasePossiblyDeadInstructionTree(Cond);
return true;
}
}
// If there is a trivial two-entry PHI node in this basic block, and we can
// eliminate it, do so now.
if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))