[cfe-commits] r150798 - in /cfe/trunk: lib/CodeGen/CGDeclCXX.cpp test/CodeGenCXX/init-invariant.cpp

[Chris Lattner]

On Feb 16, 2012, at 11:31 PM, Richard Smith wrote:

> Author: rsmith
> Date: Fri Feb 17 01:31:37 2012
> New Revision: 150798
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=150798&view=rev
> Log:
> 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.

Hi Richard,

We should only emit metadata like this when optimizations are enabled, not at -O0.

-Chris

> 
> Added:
>    cfe/trunk/test/CodeGenCXX/init-invariant.cpp
> Modified:
>    cfe/trunk/lib/CodeGen/CGDeclCXX.cpp
> 
> Modified: cfe/trunk/lib/CodeGen/CGDeclCXX.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDeclCXX.cpp?rev=150798&r1=150797&r2=150798&view=diff
> ==============================================================================
> --- cfe/trunk/lib/CodeGen/CGDeclCXX.cpp (original)
> +++ cfe/trunk/lib/CodeGen/CGDeclCXX.cpp Fri Feb 17 01:31:37 2012
> @@ -101,6 +101,19 @@
>   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 @@
>   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;
>   }
> 
> 
> Added: cfe/trunk/test/CodeGenCXX/init-invariant.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/init-invariant.cpp?rev=150798&view=auto
> ==============================================================================
> --- cfe/trunk/test/CodeGenCXX/init-invariant.cpp (added)
> +++ cfe/trunk/test/CodeGenCXX/init-invariant.cpp Fri Feb 17 01:31:37 2012
> @@ -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
> 
> 
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