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More aggressively sink GEP offsets into loops. For example, before we

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generated:

        movl 8(%esp), %eax
        movl %eax, %edx
        addl $4316, %edx
        cmpb $1, %cl
        ja LBB1_2       #cond_false
LBB1_1: #cond_true
        movl L_QuantizationTables720$non_lazy_ptr, %ecx
        movl %ecx, (%edx)
        movl L_QNOtoQuantTableShift720$non_lazy_ptr, %edx
        movl %edx, 4460(%eax)
        ret
...

Now we generate:

        movl 8(%esp), %eax
        cmpb $1, %cl
        ja LBB1_2       #cond_false
LBB1_1: #cond_true
        movl L_QuantizationTables720$non_lazy_ptr, %ecx
        movl %ecx, 4316(%eax)
        movl L_QNOtoQuantTableShift720$non_lazy_ptr, %ecx
        movl %ecx, 4460(%eax)
        ret

... which uses one fewer register.

llvm-svn: 28129
This commit is contained in:
Chris Lattner 2006-05-05 21:17:49 +00:00
parent 73bfc4c2ea
commit 229d3e3c2d
1 changed files with 121 additions and 62 deletions
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183
lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
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@ -2733,6 +2733,60 @@ void SelectionDAGISel::getAnalysisUsage(AnalysisUsage &AU) const {
}
/// OptimizeNoopCopyExpression - We have determined that the specified cast
/// instruction is a noop copy (e.g. it's casting from one pointer type to
/// another, int->uint, or int->sbyte on PPC.
///
/// Return true if any changes are made.
static bool OptimizeNoopCopyExpression(CastInst *CI) {
BasicBlock *DefBB = CI->getParent();
/// InsertedCasts - Only insert a cast in each block once.
std::map<BasicBlock*, CastInst*> InsertedCasts;
bool MadeChange = false;
for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end();
UI != E; ) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI);
// Figure out which BB this cast is used in. For PHI's this is the
// appropriate predecessor block.
BasicBlock *UserBB = User->getParent();
if (PHINode *PN = dyn_cast<PHINode>(User)) {
unsigned OpVal = UI.getOperandNo()/2;
UserBB = PN->getIncomingBlock(OpVal);
}
// Preincrement use iterator so we don't invalidate it.
++UI;
// If this user is in the same block as the cast, don't change the cast.
if (UserBB == DefBB) continue;
// If we have already inserted a cast into this block, use it.
CastInst *&InsertedCast = InsertedCasts[UserBB];
if (!InsertedCast) {
BasicBlock::iterator InsertPt = UserBB->begin();
while (isa<PHINode>(InsertPt)) ++InsertPt;
InsertedCast =
new CastInst(CI->getOperand(0), CI->getType(), "", InsertPt);
MadeChange = true;
}
// Replace a use of the cast with a use of the new casat.
TheUse = InsertedCast;
}
// If we removed all uses, nuke the cast.
if (CI->use_empty())
CI->eraseFromParent();
return MadeChange;
}
/// InsertGEPComputeCode - Insert code into BB to compute Ptr+PtrOffset,
/// casting to the type of GEPI.
static Value *InsertGEPComputeCode(Value *&V, BasicBlock *BB, Instruction *GEPI,
@ -2763,57 +2817,59 @@ static Value *InsertGEPComputeCode(Value *&V, BasicBlock *BB, Instruction *GEPI,
return V = Ptr;
}
/// OptimizeNoopCopyExpression - We have determined that the specified cast
/// instruction is a noop copy (e.g. it's casting from one pointer type to
/// another, int->uint, or int->sbyte on PPC.
static void OptimizeNoopCopyExpression(CastInst *CI) {
BasicBlock *DefBB = CI->getParent();
/// InsertedCasts - Only insert a cast in each block once.
std::map<BasicBlock*, CastInst*> InsertedCasts;
for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end();
UI != E; ) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI);
/// ReplaceUsesOfGEPInst - Replace all uses of RepPtr with inserted code to
/// compute its value. The RepPtr value can be computed with Ptr+PtrOffset. One
/// trivial way of doing this would be to evaluate Ptr+PtrOffset in RepPtr's
/// block, then ReplaceAllUsesWith'ing everything. However, we would prefer to
/// sink PtrOffset into user blocks where doing so will likely allow us to fold
/// the constant add into a load or store instruction. Additionally, if a user
/// is a pointer-pointer cast, we look through it to find its users.
static void ReplaceUsesOfGEPInst(Instruction *RepPtr, Value *Ptr,
Constant *PtrOffset, BasicBlock *DefBB,
GetElementPtrInst *GEPI,
std::map<BasicBlock*,Value*> &InsertedExprs) {
while (!RepPtr->use_empty()) {
Instruction *User = cast<Instruction>(RepPtr->use_back());
// Figure out which BB this cast is used in. For PHI's this is the
// appropriate predecessor block.
BasicBlock *UserBB = User->getParent();
if (PHINode *PN = dyn_cast<PHINode>(User)) {
unsigned OpVal = UI.getOperandNo()/2;
UserBB = PN->getIncomingBlock(OpVal);
}
// Preincrement use iterator so we don't invalidate it.
++UI;
// If this user is in the same block as the cast, don't change the cast.
if (UserBB == DefBB) continue;
// If we have already inserted a cast into this block, use it.
CastInst *&InsertedCast = InsertedCasts[UserBB];
if (!InsertedCast) {
BasicBlock::iterator InsertPt = UserBB->begin();
while (isa<PHINode>(InsertPt)) ++InsertPt;
// If the user is a Pointer-Pointer cast, recurse.
if (isa<CastInst>(User) && isa<PointerType>(User->getType())) {
ReplaceUsesOfGEPInst(User, Ptr, PtrOffset, DefBB, GEPI, InsertedExprs);
InsertedCast =
new CastInst(CI->getOperand(0), CI->getType(), "", InsertPt);
// Drop the use of RepPtr. The cast is dead. Don't delete it now, else we
// could invalidate an iterator.
User->setOperand(0, UndefValue::get(RepPtr->getType()));
continue;
}
// Replace a use of the cast with a use of the new casat.
TheUse = InsertedCast;
// If this is a load of the pointer, or a store through the pointer, emit
// the increment into the load/store block.
Value *NewVal;
if (isa<LoadInst>(User) ||
(isa<StoreInst>(User) && User->getOperand(0) != RepPtr)) {
NewVal = InsertGEPComputeCode(InsertedExprs[User->getParent()],
User->getParent(), GEPI,
Ptr, PtrOffset);
} else {
// If this use is not foldable into the addressing mode, use a version
// emitted in the GEP block.
NewVal = InsertGEPComputeCode(InsertedExprs[DefBB], DefBB, GEPI,
Ptr, PtrOffset);
}
if (GEPI->getType() != RepPtr->getType())
NewVal = new CastInst(NewVal, RepPtr->getType(), "", User);
User->replaceUsesOfWith(RepPtr, NewVal);
}
}
/// OptimizeGEPExpression - Since we are doing basic-block-at-a-time instruction
/// selection, we want to be a bit careful about some things. In particular, if
/// we have a GEP instruction that is used in a different block than it is
/// defined, the addressing expression of the GEP cannot be folded into loads or
/// stores that use it. In this case, decompose the GEP and move constant
/// indices into blocks that use it.
static void OptimizeGEPExpression(GetElementPtrInst *GEPI,
static bool OptimizeGEPExpression(GetElementPtrInst *GEPI,
const TargetData *TD) {
// If this GEP is only used inside the block it is defined in, there is no
// need to rewrite it.
@ -2826,21 +2882,36 @@ static void OptimizeGEPExpression(GetElementPtrInst *GEPI,
break;
}
}
if (!isUsedOutsideDefBB) return;
if (!isUsedOutsideDefBB) return false;
// If this GEP has no non-zero constant indices, there is nothing we can do,
// ignore it.
bool hasConstantIndex = false;
bool hasVariableIndex = false;
for (GetElementPtrInst::op_iterator OI = GEPI->op_begin()+1,
E = GEPI->op_end(); OI != E; ++OI) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(*OI))
if (ConstantInt *CI = dyn_cast<ConstantInt>(*OI)) {
if (CI->getRawValue()) {
hasConstantIndex = true;
break;
}
} else {
hasVariableIndex = true;
}
}
// If this is a "GEP X, 0, 0, 0", turn this into a cast.
if (!hasConstantIndex && !hasVariableIndex) {
Value *NC = new CastInst(GEPI->getOperand(0), GEPI->getType(),
GEPI->getName(), GEPI);
GEPI->replaceAllUsesWith(NC);
GEPI->eraseFromParent();
return true;
}
// If this is a GEP &Alloca, 0, 0, forward subst the frame index into uses.
if (!hasConstantIndex && !isa<AllocaInst>(GEPI->getOperand(0))) return;
if (!hasConstantIndex && !isa<AllocaInst>(GEPI->getOperand(0)))
return false;
// Otherwise, decompose the GEP instruction into multiplies and adds. Sum the
// constant offset (which we now know is non-zero) and deal with it later.
@ -2900,28 +2971,12 @@ static void OptimizeGEPExpression(GetElementPtrInst *GEPI,
// won't be foldable as addresses, so we might as well share the computation).
std::map<BasicBlock*,Value*> InsertedExprs;
while (!GEPI->use_empty()) {
Instruction *User = cast<Instruction>(GEPI->use_back());
// If this use is not foldable into the addressing mode, use a version
// emitted in the GEP block.
Value *NewVal;
if (!isa<LoadInst>(User) &&
(!isa<StoreInst>(User) || User->getOperand(0) == GEPI)) {
NewVal = InsertGEPComputeCode(InsertedExprs[DefBB], DefBB, GEPI,
Ptr, PtrOffset);
} else {
// Otherwise, insert the code in the User's block so it can be folded into
// any users in that block.
NewVal = InsertGEPComputeCode(InsertedExprs[User->getParent()],
User->getParent(), GEPI,
Ptr, PtrOffset);
}
User->replaceUsesOfWith(GEPI, NewVal);
}
ReplaceUsesOfGEPInst(GEPI, Ptr, PtrOffset, DefBB, GEPI, InsertedExprs);
// Finally, the GEP is dead, remove it.
GEPI->eraseFromParent();
return true;
}
bool SelectionDAGISel::runOnFunction(Function &Fn) {
@ -2938,6 +2993,9 @@ bool SelectionDAGISel::runOnFunction(Function &Fn) {
// selection.
//
//
bool MadeChange = true;
while (MadeChange) {
MadeChange = false;
for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
PHINode *PN;
BasicBlock::iterator BBI;
@ -2949,7 +3007,7 @@ bool SelectionDAGISel::runOnFunction(Function &Fn) {
for (BasicBlock::iterator E = BB->end(); BBI != E; ) {
Instruction *I = BBI++;
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
OptimizeGEPExpression(GEPI, TLI.getTargetData());
MadeChange |= OptimizeGEPExpression(GEPI, TLI.getTargetData());
} else if (CastInst *CI = dyn_cast<CastInst>(I)) {
// If this is a noop copy, sink it into user blocks to reduce the number
// of virtual registers that must be created and coallesced.
@ -2974,10 +3032,11 @@ bool SelectionDAGISel::runOnFunction(Function &Fn) {
// If, after promotion, these are the same types, this is a noop copy.
if (SrcVT == DstVT)
OptimizeNoopCopyExpression(CI);
MadeChange |= OptimizeNoopCopyExpression(CI);
}
}
}
}
FunctionLoweringInfo FuncInfo(TLI, Fn, MF);