r325478 - [CodeGen] Initialize large arrays by copying from a global
Ivan A. Kosarev via cfe-commits
cfe-commits at lists.llvm.org
Mon Feb 19 01:49:11 PST 2018
Author: kosarev
Date: Mon Feb 19 01:49:11 2018
New Revision: 325478
URL: http://llvm.org/viewvc/llvm-project?rev=325478&view=rev
Log:
[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
Modified:
cfe/trunk/lib/CodeGen/CGExprAgg.cpp
cfe/trunk/test/CodeGen/init.c
Modified: cfe/trunk/lib/CodeGen/CGExprAgg.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGExprAgg.cpp?rev=325478&r1=325477&r2=325478&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGExprAgg.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGExprAgg.cpp Mon Feb 19 01:49:11 2018
@@ -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(Addre
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(I
// Handle initialization of an array.
if (E->getType()->isArrayType()) {
- QualType elementType =
- CGF.getContext().getAsArrayType(E->getType())->getElementType();
-
auto AType = cast<llvm::ArrayType>(Dest.getAddress().getElementType());
- EmitArrayInit(Dest.getAddress(), AType, elementType, E);
+ EmitArrayInit(Dest.getAddress(), AType, E->getType(), E);
return;
}
Modified: cfe/trunk/test/CodeGen/init.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/init.c?rev=325478&r1=325477&r2=325478&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/init.c (original)
+++ cfe/trunk/test/CodeGen/init.c Mon Feb 19 01:49:11 2018
@@ -8,8 +8,9 @@ unsigned v2[2][3] = {[0 ... 1][0 ... 1]
// CHECK-DAG: %struct.M = type { [2 x %struct.I] }
// CHECK-DAG: %struct.I = type { [3 x i32] }
-// CHECK: [1 x %struct.M] [%struct.M { [2 x %struct.I] [%struct.I { [3 x i32] [i32 4, i32 4, i32 0] }, %struct.I { [3 x i32] [i32 4, i32 4, i32 5] }] }],
-// CHECK: [2 x [3 x i32]] {{[[][[]}}3 x i32] [i32 2222, i32 2222, i32 0], [3 x i32] [i32 2222, i32 2222, i32 3333]],
+// CHECK-DAG: [1 x %struct.M] [%struct.M { [2 x %struct.I] [%struct.I { [3 x i32] [i32 4, i32 4, i32 0] }, %struct.I { [3 x i32] [i32 4, i32 4, i32 5] }] }],
+// CHECK-DAG: [2 x [3 x i32]] {{[[][[]}}3 x i32] [i32 2222, i32 2222, i32 0], [3 x i32] [i32 2222, i32 2222, i32 3333]],
+// CHECK-DAG: [[INIT14:.*]] = private global [16 x i32] [i32 0, i32 0, i32 0, i32 0, i32 0, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 0, i32 0, i32 0, i32 0], align 4
void f1() {
// Scalars in braces.
@@ -33,8 +34,8 @@ void f3() {
}
// Constants
-// CHECK: @g3 = constant i32 10
-// CHECK: @f4.g4 = internal constant i32 12
+// CHECK-DAG: @g3 = constant i32 10
+// CHECK-DAG: @f4.g4 = internal constant i32 12
const int g3 = 10;
int f4() {
static const int g4 = 12;
@@ -61,7 +62,7 @@ void f6() {
-// CHECK: @test7 = global{{.*}}{ i32 0, [4 x i8] c"bar\00" }
+// CHECK-DAG: @test7 = global{{.*}}{ i32 0, [4 x i8] c"bar\00" }
// PR8217
struct a7 {
int b;
@@ -151,3 +152,15 @@ void PR20473() {
// CHECK: memcpy{{.*}}getelementptr inbounds ([3 x i8], [3 x i8]* @
bar((char[3]) {""});
}
+
+// Test that we initialize large member arrays by copying from a global and not
+// with a series of stores.
+struct S14 { int a[16]; };
+
+void test14(struct S14 *s14) {
+// CHECK-LABEL: @test14
+// CHECK: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 {{.*}}, i8* align 4 {{.*}} [[INIT14]] {{.*}}, i32 64, i1 false)
+// CHECK-NOT: store
+// CHECK: ret void
+ *s14 = (struct S14) { { [5 ... 11] = 17 } };
+}
More information about the cfe-commits
mailing list