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llvm-project/clang/lib/Parse
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George Karpenkov ec38cf7aed [ast] Do not auto-initialize Objective-C for-loop variables in Objective-C++ in templatized code under ARC 
The AST for the fragment

```
@interface I
@end

template <typename>
void decode(I *p) {
  for (I *k in p) {}
}

void decode(I *p) {
  decode<int>(p);
}
```

differs heavily when templatized and non-templatized:

```
|-FunctionTemplateDecl 0x7fbfe0863940 <line:4:1, line:7:1> line:5:6 decode
| |-TemplateTypeParmDecl 0x7fbfe0863690 <line:4:11> col:11 typename depth 0 index 0
| |-FunctionDecl 0x7fbfe08638a0 <line:5:1, line:7:1> line:5:6 decode 'void (I *__strong)'
| | |-ParmVarDecl 0x7fbfe08637a0 <col:13, col:16> col:16 referenced p 'I *__strong'
| | `-CompoundStmt 0x7fbfe0863b88 <col:19, line:7:1>
| |   `-ObjCForCollectionStmt 0x7fbfe0863b50 <line:6:3, col:20>
| |     |-DeclStmt 0x7fbfe0863a50 <col:8, col:13>
| |     | `-VarDecl 0x7fbfe08639f0 <col:8, col:11> col:11 k 'I *const __strong'
| |     |-ImplicitCastExpr 0x7fbfe0863a90 <col:16> 'I *' <LValueToRValue>
| |     | `-DeclRefExpr 0x7fbfe0863a68 <col:16> 'I *__strong' lvalue ParmVar 0x7fbfe08637a0 'p' 'I *__strong'
| |     `-CompoundStmt 0x7fbfe0863b78 <col:19, col:20>
| `-FunctionDecl 0x7fbfe0863f80 <line:5:1, line:7:1> line:5:6 used decode 'void (I *__strong)'
|   |-TemplateArgument type 'int'
|   |-ParmVarDecl 0x7fbfe0863ef8 <col:13, col:16> col:16 used p 'I *__strong'
|   `-CompoundStmt 0x7fbfe0890cf0 <col:19, line:7:1>
|     `-ObjCForCollectionStmt 0x7fbfe0890cc8 <line:6:3, col:20>
|       |-DeclStmt 0x7fbfe0890c70 <col:8, col:13>
|       | `-VarDecl 0x7fbfe0890c00 <col:8, col:11> col:11 k 'I *__strong' callinit
|       |   `-ImplicitValueInitExpr 0x7fbfe0890c60 <<invalid sloc>> 'I *__strong'
|       |-ImplicitCastExpr 0x7fbfe0890cb0 <col:16> 'I *' <LValueToRValue>
|       | `-DeclRefExpr 0x7fbfe0890c88 <col:16> 'I *__strong' lvalue ParmVar 0x7fbfe0863ef8 'p' 'I *__strong'
|       `-CompoundStmt 0x7fbfe0863b78 <col:19, col:20>
```

Note how in the instantiated version ImplicitValueInitExpr unexpectedly appears.

While objects are auto-initialized under ARC, it does not make sense to
have an initializer for a for-loop variable, and it makes even less
sense to have such a different AST for instantiated and non-instantiated
version.

Digging deeper, I have found that there are two separate Sema* files for
dealing with templates and for dealing with non-templatized code.
In a non-templatized version, an initialization was performed only for
variables which are not loop variables for an Objective-C loop and not
variables for a C++ for-in loop:

```
  if (FRI && (Tok.is(tok::colon) || isTokIdentifier_in())) {
    bool IsForRangeLoop = false;
    if (TryConsumeToken(tok::colon, FRI->ColonLoc)) {
      IsForRangeLoop = true;
      if (Tok.is(tok::l_brace))
        FRI->RangeExpr = ParseBraceInitializer();
      else
        FRI->RangeExpr = ParseExpression();
    }

    Decl *ThisDecl = Actions.ActOnDeclarator(getCurScope(), D);
    if (IsForRangeLoop)
      Actions.ActOnCXXForRangeDecl(ThisDecl);
    Actions.FinalizeDeclaration(ThisDecl);
    D.complete(ThisDecl);
    return Actions.FinalizeDeclaratorGroup(getCurScope(), DS, ThisDecl);
  }

  SmallVector<Decl *, 8> DeclsInGroup;
  Decl *FirstDecl = ParseDeclarationAfterDeclaratorAndAttributes(
      D, ParsedTemplateInfo(), FRI);
```

However the code in SemaTemplateInstantiateDecl was inconsistent,
guarding only against C++ for-in loops.

rdar://38391075

Differential Revision: https://reviews.llvm.org/D44989

llvm-svn: 328749
 		2018-03-29 00:56:24 +00:00
..
CMakeLists.txt
…
ParseAST.cpp [Templight] Template Instantiation Observer 2018-02-10 14:04:45 +00:00
ParseCXXInlineMethods.cpp PR34163: Don't cache an incorrect key function for a class if queried between 2017-08-12 01:46:03 +00:00
ParseDecl.cpp [ast] Do not auto-initialize Objective-C for-loop variables in Objective-C++ in templatized code under ARC 2018-03-29 00:56:24 +00:00
ParseDeclCXX.cpp Fix some handling of AST nodes with diagnostics. 2018-03-28 04:16:13 +00:00
ParseExpr.cpp Again reverting an attempt to convert the DeclSpec enums into scoped enums. 2018-01-01 18:23:28 +00:00
ParseExprCXX.cpp [C++17] Allow an empty expression in an if init statement 2018-03-17 21:42:10 +00:00
ParseInit.cpp Added LLVM_FALLTHROUGH to address warning: this statement may fall through. NFC. 2017-06-01 21:23:52 +00:00
ParseObjc.cpp Sink PrettyDeclStackTrace down to the AST library 2018-03-23 00:07:18 +00:00
ParseOpenMP.cpp [OPENMP] Codegen for ctor|dtor of declare target variables. 2018-03-28 14:28:54 +00:00
ParsePragma.cpp [ms] Parse #pragma optimize and ignore it behind its own flag 2018-03-20 08:53:11 +00:00
ParseStmt.cpp Sink PrettyDeclStackTrace down to the AST library 2018-03-23 00:07:18 +00:00
ParseStmtAsm.cpp Move MS inline asm parser methods out of line to reduce indentation, NFC 2017-10-26 17:07:48 +00:00
ParseTemplate.cpp Fix a couple of cases where we would fail to correctly parse deduced class template specialization types. 2018-02-28 03:02:23 +00:00
ParseTentative.cpp [MS] Accept __unaligned as a qualifier on member function pointers 2018-03-07 23:26:02 +00:00
Parser.cpp [Parser] Remove hard-coded bracket depth limit 2018-03-16 20:17:28 +00:00