From e0ef348cb9c50d56be935e856c81e48cc1e744bd Mon Sep 17 00:00:00 2001 From: "Ivan A. Kosarev" Date: Mon, 19 Feb 2018 09:49:11 +0000 Subject: [CodeGen] Initialize large arrays by copying from a global Currently, clang compiles explicit initializers for array elements into series of store instructions. For large arrays of built-in types this results in bloated output code and significant amount of time spent on the instruction selection phase. This patch fixes the issue by initializing such arrays with global constants that store the binary image of the initializer. Differential Revision: https://reviews.llvm.org/D43181 llvm-svn: 325478 --- clang/lib/CodeGen/CGExprAgg.cpp | 36 ++++++++++++++++++++++++++++++------ 1 file changed, 30 insertions(+), 6 deletions(-) (limited to 'clang/lib/CodeGen/CGExprAgg.cpp') diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp index d2b29e06ae3..34ce0d3398f 100644 --- a/clang/lib/CodeGen/CGExprAgg.cpp +++ b/clang/lib/CodeGen/CGExprAgg.cpp @@ -14,6 +14,7 @@ #include "CodeGenFunction.h" #include "CGObjCRuntime.h" #include "CodeGenModule.h" +#include "ConstantEmitter.h" #include "clang/AST/ASTContext.h" #include "clang/AST/DeclCXX.h" #include "clang/AST/DeclTemplate.h" @@ -85,7 +86,7 @@ public: void EmitMoveFromReturnSlot(const Expr *E, RValue Src); void EmitArrayInit(Address DestPtr, llvm::ArrayType *AType, - QualType elementType, InitListExpr *E); + QualType ArrayQTy, InitListExpr *E); AggValueSlot::NeedsGCBarriers_t needsGC(QualType T) { if (CGF.getLangOpts().getGC() && TypeRequiresGCollection(T)) @@ -394,12 +395,15 @@ static bool isTrivialFiller(Expr *E) { /// \brief Emit initialization of an array from an initializer list. void AggExprEmitter::EmitArrayInit(Address DestPtr, llvm::ArrayType *AType, - QualType elementType, InitListExpr *E) { + QualType ArrayQTy, InitListExpr *E) { uint64_t NumInitElements = E->getNumInits(); uint64_t NumArrayElements = AType->getNumElements(); assert(NumInitElements <= NumArrayElements); + QualType elementType = + CGF.getContext().getAsArrayType(ArrayQTy)->getElementType(); + // DestPtr is an array*. Construct an elementType* by drilling // down a level. llvm::Value *zero = llvm::ConstantInt::get(CGF.SizeTy, 0); @@ -411,6 +415,29 @@ void AggExprEmitter::EmitArrayInit(Address DestPtr, llvm::ArrayType *AType, CharUnits elementAlign = DestPtr.getAlignment().alignmentOfArrayElement(elementSize); + // Consider initializing the array by copying from a global. For this to be + // more efficient than per-element initialization, the size of the elements + // with explicit initializers should be large enough. + if (NumInitElements * elementSize.getQuantity() > 16 && + elementType.isTriviallyCopyableType(CGF.getContext())) { + CodeGen::CodeGenModule &CGM = CGF.CGM; + ConstantEmitter Emitter(CGM); + LangAS AS = ArrayQTy.getAddressSpace(); + if (llvm::Constant *C = Emitter.tryEmitForInitializer(E, AS, ArrayQTy)) { + auto GV = new llvm::GlobalVariable( + CGM.getModule(), C->getType(), + CGM.isTypeConstant(ArrayQTy, /* ExcludeCtorDtor= */ true), + llvm::GlobalValue::PrivateLinkage, C, "constinit", + /* InsertBefore= */ nullptr, llvm::GlobalVariable::NotThreadLocal, + CGM.getContext().getTargetAddressSpace(AS)); + Emitter.finalize(GV); + CharUnits Align = CGM.getContext().getTypeAlignInChars(ArrayQTy); + GV->setAlignment(Align.getQuantity()); + EmitFinalDestCopy(ArrayQTy, CGF.MakeAddrLValue(GV, ArrayQTy, Align)); + return; + } + } + // Exception safety requires us to destroy all the // already-constructed members if an initializer throws. // For that, we'll need an EH cleanup. @@ -1158,11 +1185,8 @@ void AggExprEmitter::VisitInitListExpr(InitListExpr *E) { // Handle initialization of an array. if (E->getType()->isArrayType()) { - QualType elementType = - CGF.getContext().getAsArrayType(E->getType())->getElementType(); - auto AType = cast(Dest.getAddress().getElementType()); - EmitArrayInit(Dest.getAddress(), AType, elementType, E); + EmitArrayInit(Dest.getAddress(), AType, E->getType(), E); return; } -- cgit v1.2.3