On 21 May 2018 at 09:09, Serge Pavlov via cfe-commits < cfe-commits@lists.llvm.org> wrote:
> Author: sepavloff > Date: Mon May 21 09:09:54 2018 > New Revision: 332847 > > URL: http://llvm.org/viewvc/llvm-project?rev=332847&view=rev > Log: > [CodeGen] Recognize more cases of zero initialization > > If a variable has an initializer, codegen tries to build its value. If > the variable is large in size, building its value requires substantial > resources. It causes strange behavior from user viewpoint: compilation > of huge zero initialized arrays like: > > char data_1[2147483648u] = { 0 }; > > consumes enormous amount of time and memory. > > With this change codegen tries to determine if variable initializer is > equivalent to zero initializer. In this case variable value is not > constructed. > > This change fixes PR18978. > > Differential Revision: https://reviews.llvm.org/D46241 > > Removed: > cfe/trunk/test/SemaCXX/large-array-init.cpp > Modified: > cfe/trunk/include/clang/AST/Expr.h > cfe/trunk/lib/AST/ExprConstant.cpp > cfe/trunk/lib/CodeGen/CGExprConstant.cpp > cfe/trunk/test/CodeGen/const-init.c > cfe/trunk/test/CodeGen/designated-initializers.c > cfe/trunk/test/CodeGen/union-init2.c > cfe/trunk/test/CodeGenCXX/cxx11-initializer-aggregate.cpp > cfe/trunk/test/CodeGenCXX/cxx1z-initializer-aggregate.cpp > > Modified: cfe/trunk/include/clang/AST/Expr.h > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/ > clang/AST/Expr.h?rev=332847&r1=332846&r2=332847&view=diff > ============================================================ > ================== > --- cfe/trunk/include/clang/AST/Expr.h (original) > +++ cfe/trunk/include/clang/AST/Expr.h Mon May 21 09:09:54 2018 > @@ -537,6 +537,13 @@ public: > bool isConstantInitializer(ASTContext &Ctx, bool ForRef, > const Expr **Culprit = nullptr) const; > > + enum SideEffectsKind { > + SE_NoSideEffects, ///< Strictly evaluate the expression. > + SE_AllowUndefinedBehavior, ///< Allow UB that we can give a value, > but not > + ///< arbitrary unmodeled side effects. > + SE_AllowSideEffects ///< Allow any unmodeled side effect. > + }; > + > /// EvalStatus is a struct with detailed info about an evaluation in > progress. > struct EvalStatus { > /// Whether the evaluated expression has side effects. > @@ -565,6 +572,11 @@ public: > bool hasSideEffects() const { > return HasSideEffects; > } > + > + bool hasUnacceptableSideEffect(SideEffectsKind SEK) { > + return (SEK < SE_AllowSideEffects && HasSideEffects) || > + (SEK < SE_AllowUndefinedBehavior && HasUndefinedBehavior); > + } > }; > > /// EvalResult is a struct with detailed info about an evaluated > expression. > @@ -591,13 +603,6 @@ public: > /// side-effects. > bool EvaluateAsBooleanCondition(bool &Result, const ASTContext &Ctx) > const; > > - enum SideEffectsKind { > - SE_NoSideEffects, ///< Strictly evaluate the expression. > - SE_AllowUndefinedBehavior, ///< Allow UB that we can give a value, > but not > - ///< arbitrary unmodeled side effects. > - SE_AllowSideEffects ///< Allow any unmodeled side effect. > - }; > - > /// EvaluateAsInt - Return true if this is a constant which we can fold > and > /// convert to an integer, using any crazy technique that we want to. > bool EvaluateAsInt(llvm::APSInt &Result, const ASTContext &Ctx, > > Modified: cfe/trunk/lib/AST/ExprConstant.cpp > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ > ExprConstant.cpp?rev=332847&r1=332846&r2=332847&view=diff > ============================================================ > ================== > --- cfe/trunk/lib/AST/ExprConstant.cpp (original) > +++ cfe/trunk/lib/AST/ExprConstant.cpp Mon May 21 09:09:54 2018 > @@ -10312,12 +10312,6 @@ bool Expr::EvaluateAsBooleanCondition(bo > HandleConversionToBool(Scratch.Val, Result); > } > > -static bool hasUnacceptableSideEffect(Expr::EvalStatus &Result, > - Expr::SideEffectsKind SEK) { > - return (SEK < Expr::SE_AllowSideEffects && Result.HasSideEffects) || > - (SEK < Expr::SE_AllowUndefinedBehavior && > Result.HasUndefinedBehavior); > -} > - > bool Expr::EvaluateAsInt(APSInt &Result, const ASTContext &Ctx, > SideEffectsKind AllowSideEffects) const { > if (!getType()->isIntegralOrEnumerationType()) > @@ -10325,7 +10319,7 @@ bool Expr::EvaluateAsInt(APSInt &Result, > > EvalResult ExprResult; > if (!EvaluateAsRValue(ExprResult, Ctx) || !ExprResult.Val.isInt() || > - hasUnacceptableSideEffect(ExprResult, AllowSideEffects)) > + ExprResult.hasUnacceptableSideEffect(AllowSideEffects)) > return false; > > Result = ExprResult.Val.getInt(); > @@ -10339,7 +10333,7 @@ bool Expr::EvaluateAsFloat(APFloat &Resu > > EvalResult ExprResult; > if (!EvaluateAsRValue(ExprResult, Ctx) || !ExprResult.Val.isFloat() || > - hasUnacceptableSideEffect(ExprResult, AllowSideEffects)) > + ExprResult.hasUnacceptableSideEffect(AllowSideEffects)) > return false; > > Result = ExprResult.Val.getFloat(); > @@ -10417,7 +10411,7 @@ bool Expr::EvaluateAsInitializer(APValue > bool Expr::isEvaluatable(const ASTContext &Ctx, SideEffectsKind SEK) > const { > EvalResult Result; > return EvaluateAsRValue(Result, Ctx) && > - !hasUnacceptableSideEffect(Result, SEK); > + !Result.hasUnacceptableSideEffect(SEK); > } > > APSInt Expr::EvaluateKnownConstInt(const ASTContext &Ctx, > > Modified: cfe/trunk/lib/CodeGen/CGExprConstant.cpp > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/ > CGExprConstant.cpp?rev=332847&r1=332846&r2=332847&view=diff > ============================================================ > ================== > --- cfe/trunk/lib/CodeGen/CGExprConstant.cpp (original) > +++ cfe/trunk/lib/CodeGen/CGExprConstant.cpp Mon May 21 09:09:54 2018 > @@ -1392,20 +1392,40 @@ static QualType getNonMemoryType(CodeGen > return type; > } > > +/// Checks if the specified initializer is equivalent to zero > initialization. > +static bool isZeroInitializer(ConstantEmitter &CE, const Expr *Init) { > + if (auto *E = dyn_cast_or_null<CXXConstructExpr>(Init)) { > + CXXConstructorDecl *CD = E->getConstructor(); > + return CD->isDefaultConstructor() && CD->isTrivial(); > + } > + > + if (auto *IL = dyn_cast_or_null<InitListExpr>(Init)) { > + for (auto I : IL->inits()) > + if (!isZeroInitializer(CE, I)) > + return false; > + if (const Expr *Filler = IL->getArrayFiller()) > + return isZeroInitializer(CE, Filler); > + return true; > + } > + > + QualType InitTy = Init->getType(); > + if (InitTy->isIntegralOrEnumerationType() || InitTy->isPointerType()) { > + Expr::EvalResult Result; > + if (Init->EvaluateAsRValue(Result, CE.CGM.getContext()) && > + !Result.hasUnacceptableSideEffect(Expr::SE_NoSideEffects)) > As I mentioned on the review thread, this is wrong, and you need to call D->evaluateValue() here instead. > + return (Result.Val.isInt() && Result.Val.getInt().isNullValue()) || > + (Result.Val.isLValue() && Result.Val.isNullPointer()); > + } > + > + return false; > +} > + > llvm::Constant *ConstantEmitter::tryEmitPrivateForVarInit(const VarDecl > &D) { > // Make a quick check if variable can be default NULL initialized > // and avoid going through rest of code which may do, for c++11, > // initialization of memory to all NULLs. > - if (!D.hasLocalStorage()) { > - QualType Ty = CGM.getContext().getBaseElementType(D.getType()); > - if (Ty->isRecordType()) > - if (const CXXConstructExpr *E = > - dyn_cast_or_null<CXXConstructExpr>(D.getInit())) { > - const CXXConstructorDecl *CD = E->getConstructor(); > - if (CD->isTrivial() && CD->isDefaultConstructor()) > - return CGM.EmitNullConstant(D.getType()); > - } > - } > + if (!D.hasLocalStorage() && isZeroInitializer(*this, D.getInit())) > + return CGM.EmitNullConstant(D.getType()); > > QualType destType = D.getType(); > > > Modified: cfe/trunk/test/CodeGen/const-init.c > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/ > CodeGen/const-init.c?rev=332847&r1=332846&r2=332847&view=diff > ============================================================ > ================== > --- cfe/trunk/test/CodeGen/const-init.c (original) > +++ cfe/trunk/test/CodeGen/const-init.c Mon May 21 09:09:54 2018 > @@ -167,7 +167,7 @@ void g30() { > int : 1; > int x; > } a = {}; > - // CHECK: @g30.a = internal global %struct.anon.1 <{ i8 undef, i32 0 > }>, align 1 > + // CHECK: @g30.a = internal global %struct.anon.1 zeroinitializer, > align 1 > #pragma pack() > } > > > Modified: cfe/trunk/test/CodeGen/designated-initializers.c > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/ > CodeGen/designated-initializers.c?rev=332847&r1=332846&r2=332847&view=diff > ============================================================ > ================== > --- cfe/trunk/test/CodeGen/designated-initializers.c (original) > +++ cfe/trunk/test/CodeGen/designated-initializers.c Mon May 21 09:09:54 > 2018 > @@ -8,7 +8,7 @@ struct foo { > // CHECK: @u = global %union.anon zeroinitializer > union { int i; float f; } u = { }; > > -// CHECK: @u2 = global { i32, [4 x i8] } { i32 0, [4 x i8] undef } > +// CHECK: @u2 = global %union.anon.0 zeroinitializer > union { int i; double f; } u2 = { }; > > // CHECK: @u3 = global %union.anon.1 zeroinitializer > > Modified: cfe/trunk/test/CodeGen/union-init2.c > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/ > CodeGen/union-init2.c?rev=332847&r1=332846&r2=332847&view=diff > ============================================================ > ================== > --- cfe/trunk/test/CodeGen/union-init2.c (original) > +++ cfe/trunk/test/CodeGen/union-init2.c Mon May 21 09:09:54 2018 > @@ -5,7 +5,7 @@ > union x {long long b;union x* a;} r = {.a = &r}; > > > -// CHECK: global { [3 x i8], [5 x i8] } { [3 x i8] zeroinitializer, [5 x > i8] undef } > +// CHECK: global %union.z zeroinitializer > union z { > char a[3]; > long long b; > > Modified: cfe/trunk/test/CodeGenCXX/cxx11-initializer-aggregate.cpp > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/ > CodeGenCXX/cxx11-initializer-aggregate.cpp?rev=332847&r1= > 332846&r2=332847&view=diff > ============================================================ > ================== > --- cfe/trunk/test/CodeGenCXX/cxx11-initializer-aggregate.cpp (original) > +++ cfe/trunk/test/CodeGenCXX/cxx11-initializer-aggregate.cpp Mon May 21 > 09:09:54 2018 > @@ -51,3 +51,30 @@ namespace NonTrivialInit { > // meaningful. > B b[30] = {}; > } > + > +namespace ZeroInit { > + enum { Zero, One }; > + constexpr int zero() { return 0; } > + constexpr int *null() { return nullptr; } > + struct Filler { > + int x; > + Filler(); > + }; > + struct S1 { > + int x; > + }; > + > + // These declarations, if implemented elementwise, require huge > + // amout of memory and compiler time. > + unsigned char data_1[1024 * 1024 * 1024 * 2u] = { 0 }; > + unsigned char data_2[1024 * 1024 * 1024 * 2u] = { Zero }; > + unsigned char data_3[1024][1024][1024] = {{{0}}}; > + unsigned char data_4[1024 * 1024 * 1024 * 2u] = { zero() }; > + int *data_5[1024 * 1024 * 512] = { nullptr }; > + int *data_6[1024 * 1024 * 512] = { null() }; > + struct S1 data_7[1024 * 1024 * 512] = {{0}}; > + > + // This variable must be initialized elementwise. > + Filler data_e1[1024] = {}; > + // CHECK: getelementptr inbounds {{.*}} @_ZN8ZeroInit7data_e1E > +} > > Modified: cfe/trunk/test/CodeGenCXX/cxx1z-initializer-aggregate.cpp > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/ > CodeGenCXX/cxx1z-initializer-aggregate.cpp?rev=332847&r1= > 332846&r2=332847&view=diff > ============================================================ > ================== > --- cfe/trunk/test/CodeGenCXX/cxx1z-initializer-aggregate.cpp (original) > +++ cfe/trunk/test/CodeGenCXX/cxx1z-initializer-aggregate.cpp Mon May 21 > 09:09:54 2018 > @@ -17,14 +17,14 @@ namespace Constant { > > C c1 = {}; > C c2 = {1}; > - // CHECK: @_ZN8Constant2c1E = global { i8 } zeroinitializer, align 1 > + // CHECK: @_ZN8Constant2c1E = global %"struct.Constant::C" > zeroinitializer, align 1 > // CHECK: @_ZN8Constant2c2E = global { i8 } { i8 1 }, align 1 > > // Test packing bases into tail padding. > D d1 = {}; > D d2 = {1, 2, 3}; > D d3 = {1}; > - // CHECK: @_ZN8Constant2d1E = global { i32, i8, i8 } zeroinitializer, > align 4 > + // CHECK: @_ZN8Constant2d1E = global %"struct.Constant::D" > zeroinitializer, align 4 > // CHECK: @_ZN8Constant2d2E = global { i32, i8, i8 } { i32 1, i8 2, i8 > 3 }, align 4 > // CHECK: @_ZN8Constant2d3E = global { i32, i8, i8 } { i32 1, i8 0, i8 > 0 }, align 4 > > > Removed: cfe/trunk/test/SemaCXX/large-array-init.cpp > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/ > SemaCXX/large-array-init.cpp?rev=332846&view=auto > ============================================================ > ================== > --- cfe/trunk/test/SemaCXX/large-array-init.cpp (original) > +++ cfe/trunk/test/SemaCXX/large-array-init.cpp (removed) > @@ -1,10 +0,0 @@ > -// RUN: %clang_cc1 -S -o %t.ll -mllvm -debug-only=exprconstant %s 2>&1 | \ > -// RUN: FileCheck %s > -// REQUIRES: asserts > - > -struct S { int i; }; > - > -static struct S arr[100000000] = {{ 0 }}; > -// CHECK: The number of elements to initialize: 1. > - > -struct S *foo() { return arr; } > > > _______________________________________________ > cfe-commits mailing list > cfe-commits@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >
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