From: Serge Pavlov Date: Mon, 21 May 2018 16:09:54 +0000 (+0000) Subject: [CodeGen] Recognize more cases of zero initialization X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=6b450481a2d4d66aa0b146a1d7fc1084c555488e;p=clang [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 git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@332847 91177308-0d34-0410-b5e6-96231b3b80d8 --- diff --git a/include/clang/AST/Expr.h b/include/clang/AST/Expr.h index 47e8261abf..a44e98b1d1 100644 --- a/include/clang/AST/Expr.h +++ b/include/clang/AST/Expr.h @@ -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, diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp index 0e1fb98bf7..3efd8dc6a6 100644 --- a/lib/AST/ExprConstant.cpp +++ b/lib/AST/ExprConstant.cpp @@ -10312,12 +10312,6 @@ bool Expr::EvaluateAsBooleanCondition(bool &Result, 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, const ASTContext &Ctx, 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 &Result, const ASTContext &Ctx, 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 &Value, const ASTContext &Ctx, 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, diff --git a/lib/CodeGen/CGExprConstant.cpp b/lib/CodeGen/CGExprConstant.cpp index 7b076ea3e6..ae05df1be5 100644 --- a/lib/CodeGen/CGExprConstant.cpp +++ b/lib/CodeGen/CGExprConstant.cpp @@ -1392,20 +1392,40 @@ static QualType getNonMemoryType(CodeGenModule &CGM, QualType type) { 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(Init)) { + CXXConstructorDecl *CD = E->getConstructor(); + return CD->isDefaultConstructor() && CD->isTrivial(); + } + + if (auto *IL = dyn_cast_or_null(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)) + 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(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(); diff --git a/test/CodeGen/const-init.c b/test/CodeGen/const-init.c index 3fd231b630..2d69995403 100644 --- a/test/CodeGen/const-init.c +++ b/test/CodeGen/const-init.c @@ -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() } diff --git a/test/CodeGen/designated-initializers.c b/test/CodeGen/designated-initializers.c index 74532c8fa5..21077b4c14 100644 --- a/test/CodeGen/designated-initializers.c +++ b/test/CodeGen/designated-initializers.c @@ -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 diff --git a/test/CodeGen/union-init2.c b/test/CodeGen/union-init2.c index bf20696a22..0b68c21112 100644 --- a/test/CodeGen/union-init2.c +++ b/test/CodeGen/union-init2.c @@ -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; diff --git a/test/CodeGenCXX/cxx11-initializer-aggregate.cpp b/test/CodeGenCXX/cxx11-initializer-aggregate.cpp index 8bf35966f5..0fb247a31c 100644 --- a/test/CodeGenCXX/cxx11-initializer-aggregate.cpp +++ b/test/CodeGenCXX/cxx11-initializer-aggregate.cpp @@ -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 +} diff --git a/test/CodeGenCXX/cxx1z-initializer-aggregate.cpp b/test/CodeGenCXX/cxx1z-initializer-aggregate.cpp index f59ec51136..ab1c6383bd 100644 --- a/test/CodeGenCXX/cxx1z-initializer-aggregate.cpp +++ b/test/CodeGenCXX/cxx1z-initializer-aggregate.cpp @@ -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 diff --git a/test/SemaCXX/large-array-init.cpp b/test/SemaCXX/large-array-init.cpp deleted file mode 100644 index ba73428059..0000000000 --- a/test/SemaCXX/large-array-init.cpp +++ /dev/null @@ -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; }