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CodeGen: Optimize emssion of zeroinitialzied arrays 

Create an ConstantAggregateZero upfront if we see that it is viable.
This saves us from having to manually push_back each and every
initializer and then looping back over them to determine if they are
'null'.

llvm-svn: 224908
This commit is contained in:
David Majnemer 2014-12-28 23:46:59 +00:00
parent 4099328596
commit 90d854489f
1 changed files with 24 additions and 12 deletions
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36
clang/lib/CodeGen/CGExprConstant.cpp
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@ -750,6 +750,20 @@ public:
// initialise any elements that have not been initialised explicitly
unsigned NumInitableElts = std::min(NumInitElements, NumElements);
// Initialize remaining array elements.
// FIXME: This doesn't handle member pointers correctly!
llvm::Constant *fillC;
if (Expr *filler = ILE->getArrayFiller())
fillC = CGM.EmitConstantExpr(filler, filler->getType(), CGF);
else
fillC = llvm::Constant::getNullValue(ElemTy);
if (!fillC)
return nullptr;
// Try to use a ConstantAggregateZero if we can.
if (fillC->isNullValue() && !NumInitableElts)
return llvm::ConstantAggregateZero::get(AType);
// Copy initializer elements.
std::vector<llvm::Constant*> Elts;
Elts.reserve(NumInitableElts + NumElements);
@ -764,15 +778,6 @@ public:
Elts.push_back(C);
}
// Initialize remaining array elements.
// FIXME: This doesn't handle member pointers correctly!
llvm::Constant *fillC;
if (Expr *filler = ILE->getArrayFiller())
fillC = CGM.EmitConstantExpr(filler, filler->getType(), CGF);
else
fillC = llvm::Constant::getNullValue(ElemTy);
if (!fillC)
return nullptr;
RewriteType |= (fillC->getType() != ElemTy);
Elts.resize(NumElements, fillC);
@ -1207,9 +1212,6 @@ llvm::Constant *CodeGenModule::EmitConstantValue(const APValue &Value,
unsigned NumElements = Value.getArraySize();
unsigned NumInitElts = Value.getArrayInitializedElts();
std::vector<llvm::Constant*> Elts;
Elts.reserve(NumElements);
// Emit array filler, if there is one.
llvm::Constant *Filler = nullptr;
if (Value.hasArrayFiller())
@ -1219,6 +1221,16 @@ llvm::Constant *CodeGenModule::EmitConstantValue(const APValue &Value,
// Emit initializer elements.
llvm::Type *CommonElementType =
getTypes().ConvertType(CAT->getElementType());
// Try to use a ConstantAggregateZero if we can.
if (Filler && Filler->isNullValue() && !NumInitElts) {
llvm::ArrayType *AType =
llvm::ArrayType::get(CommonElementType, NumElements);
return llvm::ConstantAggregateZero::get(AType);
}
std::vector<llvm::Constant*> Elts;
Elts.reserve(NumElements);
for (unsigned I = 0; I < NumElements; ++I) {
llvm::Constant *C = Filler;
if (I < NumInitElts)