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The clang half of r150794: after the construction of a global or static const 

variable ends, if the variable has a trivial destructor and no mutable
subobjects then emit an llvm.invariant.start call for it. globalopt knows to
make the variable const when evaluating this.

llvm-svn: 150798
This commit is contained in:
Richard Smith 2012-02-17 07:31:37 +00:00
parent 2939e6e136
commit 08a5144621
2 changed files with 77 additions and 1 deletions
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18
clang/lib/CodeGen/CGDeclCXX.cpp
View File

@ -101,6 +101,19 @@ static void EmitDeclDestroy(CodeGenFunction &CGF, const VarDecl &D,
CGF.EmitCXXGlobalDtorRegistration(function, argument);
}
/// Emit code to cause the variable at the given address to be considered as
/// constant from this point onwards.
static void EmitDeclInvariant(CodeGenFunction &CGF, llvm::Constant *Addr) {
// Grab the llvm.invariant.start intrinsic.
llvm::Intrinsic::ID InvStartID = llvm::Intrinsic::invariant_start;
llvm::Constant *InvariantStart = CGF.CGM.getIntrinsic(InvStartID);
// Emit a call, with size -1 signifying the whole object.
llvm::Value *Args[2] = { llvm::ConstantInt::getSigned(CGF.Int64Ty, -1),
llvm::ConstantExpr::getBitCast(Addr, CGF.Int8PtrTy)};
CGF.Builder.CreateCall(InvariantStart, Args);
}
void CodeGenFunction::EmitCXXGlobalVarDeclInit(const VarDecl &D,
llvm::Constant *DeclPtr,
bool PerformInit) {
@ -111,7 +124,10 @@ void CodeGenFunction::EmitCXXGlobalVarDeclInit(const VarDecl &D,
if (!T->isReferenceType()) {
if (PerformInit)
EmitDeclInit(*this, D, DeclPtr);
EmitDeclDestroy(*this, D, DeclPtr);
if (CGM.isTypeConstant(D.getType(), true))
EmitDeclInvariant(*this, DeclPtr);
else
EmitDeclDestroy(*this, D, DeclPtr);
return;
}

60
clang/test/CodeGenCXX/init-invariant.cpp Normal file
View File

@ -0,0 +1,60 @@
// RUN: %clang_cc1 -triple i686-linux-gnu -emit-llvm %s -o - | FileCheck %s
// Check that we add an llvm.invariant.start to mark when a global becomes
// read-only. If globalopt can fold the initializer, it will then mark the
// variable as constant.
struct A {
A() : n(42) {}
int n;
};
// CHECK: @a = global {{.*}} zeroinitializer
extern const A a = A();
struct B {
B() : n(76) {}
mutable int n;
};
// CHECK: @b = global {{.*}} zeroinitializer
extern const B b = B();
struct C {
C() : n(81) {}
~C();
int n;
};
// CHECK: @c = global {{.*}} zeroinitializer
extern const C c = C();
int f() { return 5; }
// CHECK: @d = global i32 0
extern const int d = f();
void e() {
static const A a = A();
}
// CHECK: define internal void @__cxx_global_var_init
// CHECK: call void @_ZN1AC1Ev({{.*}}* @a)
// CHECK-NEXT: call {{.*}}@llvm.invariant.start(i64 -1, i8* bitcast ({{.*}} @a to i8*))
// CHECK: define internal void @__cxx_global_var_init
// CHECK: call void @_ZN1BC1Ev({{.*}}* @b)
// CHECK-NOT: call {{.*}}@llvm.invariant.start(i64 -1, i8* bitcast ({{.*}} @b to i8*))
// CHECK: define internal void @__cxx_global_var_init
// CHECK: call void @_ZN1CC1Ev({{.*}}* @c)
// CHECK-NOT: call {{.*}}@llvm.invariant.start(i64 -1, i8* bitcast ({{.*}} @c to i8*))
// CHECK: define internal void @__cxx_global_var_init
// CHECK: call i32 @_Z1fv(
// CHECK: store {{.*}}, i32* @d
// CHECK: call {{.*}}@llvm.invariant.start(i64 -1, i8* bitcast ({{.*}} @d to i8*))
// CHECK: define void @_Z1ev(
// CHECK: call void @_ZN1AC1Ev(%struct.A* @_ZZ1evE1a)
// CHECK: call {{.*}}@llvm.invariant.start(i64 -1, i8* bitcast ({{.*}} @_ZZ1evE1a to i8*))
// CHECK-NOT: llvm.invariant.end