[cfe-dev] [llvm-dev] DeclarationName and the StringRef.

[Umesh Kalappa via cfe-dev]

Hi Eli and All ,

We added the support to rename the function name ,i.e something like "func"
to "test_func" for any function we append the string "test_",hence modified
the code @ @ lib/Sema/SemaDecl.cpp like

 static FunctionDecl* CreateNewFunctionDecl(Sema &SemaRef, Declarator &D,
                                           DeclContext *DC, QualType &R,
                                           TypeSourceInfo *TInfo,
                                           StorageClass SC,
                                           bool &IsVirtualOkay){
 DeclarationNameInfo NameInfo = SemaRef.GetNameForDeclarator(D);
 DeclarationName Name = NameInfo.getName();
 std::string ExtPreRef;

  SmallString<32> Str;
  StringRef EP = ("Test_" + Name.getAsString()).toStringRef(Str);
  const IdentifierInfo &test = SemaRef.PP.getIdentifierTable().get(EP);
  DeclarationName ExternName(&test);
   SemaRef.ExternPrefixMap[Name.getAsString()] = ExternName;
  NameInfo.setName(ExternName);

 FunctionDecl *NewFD = nullptr;
 bool isInline = D.getDeclSpec().isInlineSpecified();

}

testcase.c

int foo();
int bar();


int bar()
{
 return 1;
}


int foo()
{
        return foo() + bar();
}

int (*ptr) ();

int main()
{
        ptr =  bar;
        return ptr();
}


we we try to compile the source testcase.c ,we ended up with the below
warnings and error.

test.c:12:9: warning: implicit declaration of function 'foo' is invalid in
C99 [-Wimplicit-function-declaration]
        return foo() + bar();
               ^
DefinefooFound:foo
test.c:12:17: warning: implicit declaration of function 'bar' is invalid in
C99 [-Wimplicit-function-declaration]
        return foo() + bar();
                       ^
DefinebarFound:bar
DefinemainCome
maintest.c:19:6: error: assigning to 'int (*)()' from incompatible type
'<overloaded function type>'
        ptr = Test_list_bar;
            ^ ~~~~~~~~~~~~~
test.c:12:17: note: candidate function
        return foo() + bar();


to overcome the above issue ,we modified the source @ lib/Sema/SemaExpr.cpp
,i.e

ExprResult
Sema::ActOnIdExpression(Scope *S, CXXScopeSpec &SS,
                        SourceLocation TemplateKWLoc, UnqualifiedId &Id,
                        bool HasTrailingLParen, bool IsAddressOfOperand,
                        std::unique_ptr<CorrectionCandidateCallback> CCC,
                        bool IsInlineAsmIdentifier, Token
*KeywordReplacement) {
  assert(!(IsAddressOfOperand && HasTrailingLParen) &&
         "cannot be direct & operand and have a trailing lparen");
  if (SS.isInvalid())
    return ExprError();

  TemplateArgumentListInfo TemplateArgsBuffer;

  // Decompose the UnqualifiedId into the following data.
  DeclarationNameInfo NameInfo;
  const TemplateArgumentListInfo *TemplateArgs;
  DecomposeUnqualifiedId(Id, TemplateArgsBuffer, NameInfo, TemplateArgs);
  /* This Map will have functions that are renamed ,Key is Function Name
and Value is the DeclarationName of renamed function.*/
   if(this->ExternPrefixMap.count( NameInfo.getName().getAsString()) == 1){
                auto ExternName =
this->ExternPrefixMap.find(NameInfo.getName().getAsString());
                if(ExternName != this->ExternPrefixMap.end()){

NameInfo.setName(this->ExternPrefixMap[NameInfo.getName().getAsString()]);
                }
        }
  DeclarationName Name = NameInfo.getName();
  IdentifierInfo *II = Name.getAsIdentifierInfo();
  SourceLocation NameLoc = NameInfo.getLoc();
}


But ,we ended up with errors like ,


test.c:12:9: error: use of undeclared identifier 'Test_foo'; did you mean
'Test_foo'?
        return foo() + bar();
               ^~~
               Test_foo
test.c:10:5: note: 'Test_foo' declared here
int foo()
    ^
test.c:12:17: error: use of undeclared identifier 'Test_bar'; did you mean
'Test_bar'?
        return foo() + bar();
                       ^~~
                       Test_bar
test.c:5:5: note: 'Test_bar' declared here
int bar()
    ^

maintest.c:19:6: error: assigning to 'int (*)()' from incompatible type
'<overloaded function type>'
        ptr = bar;


debugging the same ,any inputs or suggestions or comments  here ,will be
highly appreciated .

Thank you
~Umesh




On Wed, Dec 21, 2016 at 11:34 PM, Friedman, Eli <efriedma at codeaurora.org>
wrote:

> On 12/21/2016 5:01 AM, Umesh Kalappa via llvm-dev wrote:
>
> To context was ,
>
> Basic requirement was to append extra string to the decl name  and update
> all his references to the updated name. ,
>
> So we are constructing  the DeclarationName  instance as stated below code
> snap.
> and from DeclarationName instance ,we are constructing  the
> DeclarationNameInfo and same info used to create decl spec
> with FunctionDecl::Create () .
>
> Question is ,
>
> How do ,someone instantiate   the DeclarationName instance using StringRef
> ,because in the current trunk code snap ,we see that the DeclarationName
> can be constructed using the IdentifierInfo or Objc Selector or
> CXXOperatorId  etc as argument in the constructor .
>
> The code i.e
>
> void appendExtern(StringRef Sr)
> {
>  char *ExternChar = const_cast<char *> (Sr.data());
>  *Ptr =reinterpret_cast<void *>(ExternChar);
>
>   this->ExternName = DeclarationName::getFromOpaquePtr(Ptr);
>
> }
>
> the above is kind of hack ,may result in dangling memory references ,Any
> thoughts  on this  ?
>
> we thought to change the DeclarationName class ,with adding
> new DeclarationName constructor ,that construct the DeclarationName
> instance by StringRef as argument. i.e DeclarationName(StringRef Sr) ;
>
> Before doing this ,we thought to check with community for better
> alternative / suggestions .
>
>
> Usually it's better to send questions about the clang frontend to just
> cfe-dev, rather than llvm-dev.
>
> You can use IdentifierTable::get to get an IdentifierInfo for an arbitrary
> string, then make a DeclarationName from that.
>
> -Eli
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>
>
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