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Reg2Mem cleanup and optimizations:

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- enable phi instructions demotion to stack
 - create alloca instructions in the entry block


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43208 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Anton Korobeynikov 2007-10-21 23:05:16 +00:00
parent c6185038b8
commit a024e8ceda
3 changed files with 75 additions and 27 deletions
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5
include/llvm/Transforms/Utils/Local.h
View File

@ -78,12 +78,13 @@ bool SimplifyCFG(BasicBlock *BB);
/// invalidating the SSA information for the value. It returns the pointer to
/// the alloca inserted to create a stack slot for X.
///
AllocaInst *DemoteRegToStack(Instruction &X, bool VolatileLoads = false);
AllocaInst *DemoteRegToStack(Instruction &X, bool VolatileLoads = false,
Instruction *AllocaPoint = NULL);
/// DemotePHIToStack - This function takes a virtual register computed by a phi
/// node and replaces it with a slot in the stack frame, allocated via alloca.
/// The phi node is deleted and it returns the pointer to the alloca inserted.
AllocaInst *DemotePHIToStack(PHINode *P);
AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = NULL);
} // End llvm namespace

59
lib/Transforms/Scalar/Reg2Mem.cpp
View File

@ -26,10 +26,12 @@
#include "llvm/Instructions.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/CFG.h"
#include <list>
using namespace llvm;
STATISTIC(NumDemoted, "Number of registers demoted");
STATISTIC(NumRegsDemoted, "Number of registers demoted");
STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted");
namespace {
struct VISIBILITY_HIDDEN RegToMem : public FunctionPass {
@ -43,8 +45,8 @@ namespace {
bool valueEscapes(Instruction* i) {
BasicBlock* bb = i->getParent();
for(Value::use_iterator ii = i->use_begin(), ie = i->use_end();
ii != ie; ++ii)
for (Value::use_iterator ii = i->use_begin(), ie = i->use_end();
ii != ie; ++ii)
if (cast<Instruction>(*ii)->getParent() != bb ||
isa<PHINode>(*ii))
return true;
@ -53,26 +55,57 @@ namespace {
virtual bool runOnFunction(Function &F) {
if (!F.isDeclaration()) {
//give us a clean block
BasicBlock* bbold = &F.getEntryBlock();
BasicBlock* bbnew = new BasicBlock("allocablock", &F,
&F.getEntryBlock());
new BranchInst(bbold, bbnew);
// Insert all new allocas into entry block.
BasicBlock* BBEntry = &F.getEntryBlock();
assert(pred_begin(BBEntry) == pred_end(BBEntry) &&
"Entry block to function must not have predecessors!");
//find the instructions
// Find first non-alloca instruction and create insertion point. This is
// safe if block is well-formed: it always have terminator, otherwise
// we'll get and assertion.
BasicBlock::iterator I = BBEntry->begin();
while (isa<AllocaInst>(I)) ++I;
CastInst *AllocaInsertionPoint =
CastInst::create(Instruction::BitCast,
Constant::getNullValue(Type::Int32Ty), Type::Int32Ty,
"reg2mem alloca point", I);
// Find the escaped instructions. But don't create stack slots for
// allocas in entry block.
std::list<Instruction*> worklist;
for (Function::iterator ibb = F.begin(), ibe = F.end();
ibb != ibe; ++ibb)
for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
iib != iie; ++iib) {
if(valueEscapes(iib))
if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
valueEscapes(iib)) {
worklist.push_front(&*iib);
}
}
//demote escaped instructions
NumDemoted += worklist.size();
// Demote escaped instructions
NumRegsDemoted += worklist.size();
for (std::list<Instruction*>::iterator ilb = worklist.begin(),
ile = worklist.end(); ilb != ile; ++ilb)
DemoteRegToStack(**ilb, false);
DemoteRegToStack(**ilb, false, AllocaInsertionPoint);
worklist.clear();
// Find all phi's
for (Function::iterator ibb = F.begin(), ibe = F.end();
ibb != ibe; ++ibb)
for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
iib != iie; ++iib)
if (isa<PHINode>(iib))
worklist.push_front(&*iib);
// Demote phi nodes
NumPhisDemoted += worklist.size();
for (std::list<Instruction*>::iterator ilb = worklist.begin(),
ile = worklist.end(); ilb != ile; ++ilb)
DemotePHIToStack(cast<PHINode>(*ilb), AllocaInsertionPoint);
return true;
}
return false;

38
lib/Transforms/Utils/DemoteRegToStack.cpp
View File

@ -29,14 +29,23 @@ using namespace llvm;
/// invalidating the SSA information for the value. It returns the pointer to
/// the alloca inserted to create a stack slot for I.
///
AllocaInst* llvm::DemoteRegToStack(Instruction &I, bool VolatileLoads) {
if (I.use_empty()) return 0; // nothing to do!
AllocaInst* llvm::DemoteRegToStack(Instruction &I, bool VolatileLoads,
Instruction *AllocaPoint) {
if (I.use_empty()) {
I.eraseFromParent();
return 0;
}
// Create a stack slot to hold the value.
Function *F = I.getParent()->getParent();
AllocaInst *Slot = new AllocaInst(I.getType(), 0, I.getName(),
F->getEntryBlock().begin());
AllocaInst *Slot;
if (AllocaPoint) {
Slot = new AllocaInst(I.getType(), 0, I.getName()+".reg2mem", AllocaPoint);
} else {
Function *F = I.getParent()->getParent();
Slot = new AllocaInst(I.getType(), 0, I.getName()+".reg2mem",
F->getEntryBlock().begin());
}
// Change all of the users of the instruction to read from the stack slot
// instead.
while (!I.use_empty()) {
@ -98,16 +107,21 @@ AllocaInst* llvm::DemoteRegToStack(Instruction &I, bool VolatileLoads) {
/// DemotePHIToStack - This function takes a virtual register computed by a phi
/// node and replaces it with a slot in the stack frame, allocated via alloca.
/// The phi node is deleted and it returns the pointer to the alloca inserted.
AllocaInst* llvm::DemotePHIToStack(PHINode *P) {
AllocaInst* llvm::DemotePHIToStack(PHINode *P, Instruction *AllocaPoint) {
if (P->use_empty()) {
P->eraseFromParent();
return 0;
}
// Create a stack slot to hold the value.
Function *F = P->getParent()->getParent();
AllocaInst *Slot = new AllocaInst(P->getType(), 0, P->getName(),
F->getEntryBlock().begin());
AllocaInst *Slot;
if (AllocaPoint) {
Slot = new AllocaInst(P->getType(), 0, P->getName()+".reg2mem", AllocaPoint);
} else {
Function *F = P->getParent()->getParent();
Slot = new AllocaInst(P->getType(), 0, P->getName()+".reg2mem",
F->getEntryBlock().begin());
}
// Iterate over each operand, insert store in each predecessor.
for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {