r333500 - Update NRVO logic to support early return
Author: tzik
Date: Tue May 29 20:53:16 2018
New Revision: 333500
URL: http://llvm.org/viewvc/llvm-project?rev=333500&view=rev
Log:
Update NRVO logic to support early return
Summary:
The previous implementation misses an opportunity to apply NRVO (Named Return
Value
Optimization) below. That discourages user to write early return code.
```
struct Foo {};
Foo f(bool b) {
if (b)
return Foo();
Foo oo;
return oo;
}
```
That is, we can/should apply RVO for a local variable if:
* It's directly returned by at least one return statement.
* And, all reachable return statements in its scope returns the variable
directly.
While, the previous implementation disables the RVO in a scope if there are
multiple return
statements that refers different variables.
On the new algorithm, local variables are in NRVO_Candidate state at first, and
a return
statement changes it to NRVO_Disabled for all visible variables but the return
statement refers.
Then, at the end of the function AST traversal, NRVO is enabled for variables
in NRVO_Candidate
state and refers from at least one return statement.
Reviewers: rsmith
Reviewed By: rsmith
Subscribers: xbolva00, Quuxplusone, arthur.j.odwyer, cfe-commits
Differential Revision: https://reviews.llvm.org/D47067
Added:
cfe/trunk/test/CodeGenCXX/nrvo-noopt.cpp
cfe/trunk/test/SemaCXX/nrvo-ast.cpp
Modified:
cfe/trunk/include/clang/AST/Decl.h
cfe/trunk/include/clang/Sema/Scope.h
cfe/trunk/lib/Sema/Scope.cpp
cfe/trunk/lib/Sema/SemaDecl.cpp
cfe/trunk/lib/Sema/SemaExpr.cpp
cfe/trunk/lib/Sema/SemaStmt.cpp
cfe/trunk/lib/Serialization/ASTReaderDecl.cpp
cfe/trunk/lib/Serialization/ASTWriterDecl.cpp
cfe/trunk/test/CodeGenCXX/nrvo.cpp
Modified: cfe/trunk/include/clang/AST/Decl.h
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/Decl.h?rev=333500&r1=333499&r2=333500&view=diff
==
--- cfe/trunk/include/clang/AST/Decl.h (original)
+++ cfe/trunk/include/clang/AST/Decl.h Tue May 29 20:53:16 2018
@@ -879,6 +879,12 @@ protected:
DAK_Normal
};
+ enum NRVOMode {
+NRVO_Candidate,
+NRVO_Disabled,
+NRVO_Enabled,
+ };
+
class ParmVarDeclBitfields {
friend class ASTDeclReader;
friend class ParmVarDecl;
@@ -931,7 +937,7 @@ protected:
/// Whether this local variable could be allocated in the return
/// slot of its function, enabling the named return value optimization
/// (NRVO).
-unsigned NRVOVariable : 1;
+unsigned NRVOMode : 2;
/// Whether this variable is the for-range-declaration in a C++0x
/// for-range statement.
@@ -1319,12 +1325,20 @@ public:
/// return slot when returning from the function. Within the function body,
/// each return that returns the NRVO object will have this variable as its
/// NRVO candidate.
+ NRVOMode getNRVOMode() const {
+if (isa(this))
+ return NRVO_Disabled;
+return static_cast(NonParmVarDeclBits.NRVOMode);
+ }
+ bool isNRVOCandidate() const {
+return isa(this) ? false : NonParmVarDeclBits.NRVOMode ==
NRVO_Candidate;
+ }
bool isNRVOVariable() const {
-return isa(this) ? false : NonParmVarDeclBits.NRVOVariable;
+return isa(this) ? false : NonParmVarDeclBits.NRVOMode ==
NRVO_Enabled;
}
void setNRVOVariable(bool NRVO) {
assert(!isa(this));
-NonParmVarDeclBits.NRVOVariable = NRVO;
+NonParmVarDeclBits.NRVOMode = NRVO ? NRVO_Enabled : NRVO_Disabled;
}
/// Determine whether this variable is the for-range-declaration in
Modified: cfe/trunk/include/clang/Sema/Scope.h
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Scope.h?rev=333500&r1=333499&r2=333500&view=diff
==
--- cfe/trunk/include/clang/Sema/Scope.h (original)
+++ cfe/trunk/include/clang/Sema/Scope.h Tue May 29 20:53:16 2018
@@ -201,10 +201,6 @@ private:
/// Used to determine if errors occurred in this scope.
DiagnosticErrorTrap ErrorTrap;
- /// A lattice consisting of undefined, a single NRVO candidate variable in
- /// this scope, or over-defined. The bit is true when over-defined.
- llvm::PointerIntPair NRVO;
-
void setFlags(Scope *Parent, unsigned F);
public:
@@ -466,23 +462,7 @@ public:
UsingDirectives.end());
}
- void addNRVOCandidate(VarDecl *VD) {
-if (NRVO.getInt())
- return;
-if (NRVO.getPointer() == nullptr) {
- NRVO.setPointer(VD);
- return;
-}
-if (NRVO.getPointer() != VD)
- setNoNRVO();
- }
-
- void setNoNRVO() {
-NRVO.setInt(true);
-NRVO.setPointer(nullptr);
- }
-
- void mergeNRVOIntoParent();
+ void setNRVOCandidate(VarDecl *Candidate);
/// Init - This is used by the parser to implement scope caching.
void Init(Scope *parent, unsigned flags);
Modified: cfe/trunk/lib/Sema/Scope.cpp
URL:
http://llvm.org/viewv
r335019 - Update NRVO logic to support early return (Attempt 2)
Author: tzik
Date: Mon Jun 18 21:39:07 2018
New Revision: 335019
URL: http://llvm.org/viewvc/llvm-project?rev=335019&view=rev
Log:
Update NRVO logic to support early return (Attempt 2)
Summary:
This is the second attempt of r333500 (Update NRVO logic to support early
return).
The previous one was reverted for a miscompilation for an incorrect NRVO set up
on templates such as:
```
struct Foo {};
template
T bar() {
T t;
if (false)
return T();
return t;
}
```
Where, `t` is marked as non-NRVO variable before its instantiation. However,
while its instantiation, it's left an NRVO candidate, turned into an NRVO
variable later.
Reviewers: rsmith
Reviewed By: rsmith
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D47586
Added:
cfe/trunk/test/CodeGenCXX/nrvo-noopt.cpp
cfe/trunk/test/SemaCXX/nrvo-ast.cpp
Modified:
cfe/trunk/include/clang/AST/Decl.h
cfe/trunk/include/clang/Sema/Scope.h
cfe/trunk/lib/Sema/Scope.cpp
cfe/trunk/lib/Sema/SemaDecl.cpp
cfe/trunk/lib/Sema/SemaExpr.cpp
cfe/trunk/lib/Sema/SemaStmt.cpp
cfe/trunk/lib/Sema/SemaTemplateInstantiateDecl.cpp
cfe/trunk/lib/Serialization/ASTReaderDecl.cpp
cfe/trunk/lib/Serialization/ASTWriterDecl.cpp
cfe/trunk/test/CodeGenCXX/nrvo.cpp
Modified: cfe/trunk/include/clang/AST/Decl.h
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/Decl.h?rev=335019&r1=335018&r2=335019&view=diff
==
--- cfe/trunk/include/clang/AST/Decl.h (original)
+++ cfe/trunk/include/clang/AST/Decl.h Mon Jun 18 21:39:07 2018
@@ -879,6 +879,12 @@ protected:
DAK_Normal
};
+ enum NRVOMode {
+NRVO_Candidate,
+NRVO_Disabled,
+NRVO_Enabled,
+ };
+
class ParmVarDeclBitfields {
friend class ASTDeclReader;
friend class ParmVarDecl;
@@ -931,7 +937,7 @@ protected:
/// Whether this local variable could be allocated in the return
/// slot of its function, enabling the named return value optimization
/// (NRVO).
-unsigned NRVOVariable : 1;
+unsigned NRVOMode : 2;
/// Whether this variable is the for-range-declaration in a C++0x
/// for-range statement.
@@ -1319,12 +1325,20 @@ public:
/// return slot when returning from the function. Within the function body,
/// each return that returns the NRVO object will have this variable as its
/// NRVO candidate.
+ NRVOMode getNRVOMode() const {
+if (isa(this))
+ return NRVO_Disabled;
+return static_cast(NonParmVarDeclBits.NRVOMode);
+ }
+ bool isNRVOCandidate() const {
+return isa(this) ? false : NonParmVarDeclBits.NRVOMode ==
NRVO_Candidate;
+ }
bool isNRVOVariable() const {
-return isa(this) ? false : NonParmVarDeclBits.NRVOVariable;
+return isa(this) ? false : NonParmVarDeclBits.NRVOMode ==
NRVO_Enabled;
}
void setNRVOVariable(bool NRVO) {
assert(!isa(this));
-NonParmVarDeclBits.NRVOVariable = NRVO;
+NonParmVarDeclBits.NRVOMode = NRVO ? NRVO_Enabled : NRVO_Disabled;
}
/// Determine whether this variable is the for-range-declaration in
Modified: cfe/trunk/include/clang/Sema/Scope.h
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Scope.h?rev=335019&r1=335018&r2=335019&view=diff
==
--- cfe/trunk/include/clang/Sema/Scope.h (original)
+++ cfe/trunk/include/clang/Sema/Scope.h Mon Jun 18 21:39:07 2018
@@ -201,10 +201,6 @@ private:
/// Used to determine if errors occurred in this scope.
DiagnosticErrorTrap ErrorTrap;
- /// A lattice consisting of undefined, a single NRVO candidate variable in
- /// this scope, or over-defined. The bit is true when over-defined.
- llvm::PointerIntPair NRVO;
-
void setFlags(Scope *Parent, unsigned F);
public:
@@ -466,23 +462,7 @@ public:
UsingDirectives.end());
}
- void addNRVOCandidate(VarDecl *VD) {
-if (NRVO.getInt())
- return;
-if (NRVO.getPointer() == nullptr) {
- NRVO.setPointer(VD);
- return;
-}
-if (NRVO.getPointer() != VD)
- setNoNRVO();
- }
-
- void setNoNRVO() {
-NRVO.setInt(true);
-NRVO.setPointer(nullptr);
- }
-
- void mergeNRVOIntoParent();
+ void setNRVOCandidate(VarDecl *Candidate);
/// Init - This is used by the parser to implement scope caching.
void Init(Scope *parent, unsigned flags);
Modified: cfe/trunk/lib/Sema/Scope.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/Scope.cpp?rev=335019&r1=335018&r2=335019&view=diff
==
--- cfe/trunk/lib/Sema/Scope.cpp (original)
+++ cfe/trunk/lib/Sema/Scope.cpp Mon Jun 18 21:39:07 2018
@@ -92,7 +92,6 @@ void Scope::Init(Scope *parent, unsigned
UsingDirectives.clear();
Entity = nullptr;
ErrorTrap.reset();
- NRVO.setPointerAndInt(nullptr, 0);
}
bool Scope
r335022 - Revert r335019 "Update NRVO logic to support early return (Attempt 2)"
Author: tzik
Date: Mon Jun 18 22:35:30 2018
New Revision: 335022
URL: http://llvm.org/viewvc/llvm-project?rev=335022&view=rev
Log:
Revert r335019 "Update NRVO logic to support early return (Attempt 2)"
Removed:
cfe/trunk/test/CodeGenCXX/nrvo-noopt.cpp
cfe/trunk/test/SemaCXX/nrvo-ast.cpp
Modified:
cfe/trunk/include/clang/AST/Decl.h
cfe/trunk/include/clang/Sema/Scope.h
cfe/trunk/lib/Sema/Scope.cpp
cfe/trunk/lib/Sema/SemaDecl.cpp
cfe/trunk/lib/Sema/SemaExpr.cpp
cfe/trunk/lib/Sema/SemaStmt.cpp
cfe/trunk/lib/Sema/SemaTemplateInstantiateDecl.cpp
cfe/trunk/lib/Serialization/ASTReaderDecl.cpp
cfe/trunk/lib/Serialization/ASTWriterDecl.cpp
cfe/trunk/test/CodeGenCXX/nrvo.cpp
Modified: cfe/trunk/include/clang/AST/Decl.h
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/Decl.h?rev=335022&r1=335021&r2=335022&view=diff
==
--- cfe/trunk/include/clang/AST/Decl.h (original)
+++ cfe/trunk/include/clang/AST/Decl.h Mon Jun 18 22:35:30 2018
@@ -879,12 +879,6 @@ protected:
DAK_Normal
};
- enum NRVOMode {
-NRVO_Candidate,
-NRVO_Disabled,
-NRVO_Enabled,
- };
-
class ParmVarDeclBitfields {
friend class ASTDeclReader;
friend class ParmVarDecl;
@@ -937,7 +931,7 @@ protected:
/// Whether this local variable could be allocated in the return
/// slot of its function, enabling the named return value optimization
/// (NRVO).
-unsigned NRVOMode : 2;
+unsigned NRVOVariable : 1;
/// Whether this variable is the for-range-declaration in a C++0x
/// for-range statement.
@@ -1325,20 +1319,12 @@ public:
/// return slot when returning from the function. Within the function body,
/// each return that returns the NRVO object will have this variable as its
/// NRVO candidate.
- NRVOMode getNRVOMode() const {
-if (isa(this))
- return NRVO_Disabled;
-return static_cast(NonParmVarDeclBits.NRVOMode);
- }
- bool isNRVOCandidate() const {
-return isa(this) ? false : NonParmVarDeclBits.NRVOMode ==
NRVO_Candidate;
- }
bool isNRVOVariable() const {
-return isa(this) ? false : NonParmVarDeclBits.NRVOMode ==
NRVO_Enabled;
+return isa(this) ? false : NonParmVarDeclBits.NRVOVariable;
}
void setNRVOVariable(bool NRVO) {
assert(!isa(this));
-NonParmVarDeclBits.NRVOMode = NRVO ? NRVO_Enabled : NRVO_Disabled;
+NonParmVarDeclBits.NRVOVariable = NRVO;
}
/// Determine whether this variable is the for-range-declaration in
Modified: cfe/trunk/include/clang/Sema/Scope.h
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Scope.h?rev=335022&r1=335021&r2=335022&view=diff
==
--- cfe/trunk/include/clang/Sema/Scope.h (original)
+++ cfe/trunk/include/clang/Sema/Scope.h Mon Jun 18 22:35:30 2018
@@ -201,6 +201,10 @@ private:
/// Used to determine if errors occurred in this scope.
DiagnosticErrorTrap ErrorTrap;
+ /// A lattice consisting of undefined, a single NRVO candidate variable in
+ /// this scope, or over-defined. The bit is true when over-defined.
+ llvm::PointerIntPair NRVO;
+
void setFlags(Scope *Parent, unsigned F);
public:
@@ -462,7 +466,23 @@ public:
UsingDirectives.end());
}
- void setNRVOCandidate(VarDecl *Candidate);
+ void addNRVOCandidate(VarDecl *VD) {
+if (NRVO.getInt())
+ return;
+if (NRVO.getPointer() == nullptr) {
+ NRVO.setPointer(VD);
+ return;
+}
+if (NRVO.getPointer() != VD)
+ setNoNRVO();
+ }
+
+ void setNoNRVO() {
+NRVO.setInt(true);
+NRVO.setPointer(nullptr);
+ }
+
+ void mergeNRVOIntoParent();
/// Init - This is used by the parser to implement scope caching.
void Init(Scope *parent, unsigned flags);
Modified: cfe/trunk/lib/Sema/Scope.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/Scope.cpp?rev=335022&r1=335021&r2=335022&view=diff
==
--- cfe/trunk/lib/Sema/Scope.cpp (original)
+++ cfe/trunk/lib/Sema/Scope.cpp Mon Jun 18 22:35:30 2018
@@ -92,6 +92,7 @@ void Scope::Init(Scope *parent, unsigned
UsingDirectives.clear();
Entity = nullptr;
ErrorTrap.reset();
+ NRVO.setPointerAndInt(nullptr, 0);
}
bool Scope::containedInPrototypeScope() const {
@@ -118,15 +119,19 @@ void Scope::AddFlags(unsigned FlagsToSet
Flags |= FlagsToSet;
}
-void Scope::setNRVOCandidate(VarDecl *Candidate) {
- for (Decl *D : DeclsInScope) {
-VarDecl *VD = dyn_cast(D);
-if (VD && VD != Candidate && VD->isNRVOCandidate())
- VD->setNRVOVariable(false);
+void Scope::mergeNRVOIntoParent() {
+ if (VarDecl *Candidate = NRVO.getPointer()) {
+if (isDeclScope(Candidate))
+ Candidate->setNRVOVariable(true);
}
- if (Scope *parent = getParent())
-parent->setNRVOC
