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[Macros] Copy the evaluated source into an owned memory buffer. #62440

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Merged
merged 1 commit into from
Dec 8, 2022
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[Macros] Copy the evaluated source into an owned memory buffer. #62440

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3 changes: 2 additions & 1 deletion lib/Sema/TypeCheckMacros.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -214,8 +214,9 @@ Expr *swift::expandMacroExpr(

// Create a new source buffer with the contents of the expanded macro.
auto macroBuffer =
llvm::MemoryBuffer::getMemBuffer(evaluatedSource, bufferName);
llvm::MemoryBuffer::getMemBufferCopy(evaluatedSource, bufferName);
unsigned macroBufferID = sourceMgr.addNewSourceBuffer(std::move(macroBuffer));
free((void*)evaluatedSource.data());
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@rintaro rintaro Dec 7, 2022 •
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We know it works. But still a little scary.

It would be great if there's a way to pass C++ lambda to swift_ASTGen_evaluateMacro where

  • the lambda receives a temporary C string (i.e. handler callback) 
    swift_ASTGen_evaluateMacro( ..., [&](unsigned char *utf8Start, size_t length) {
  // utf8Start is valid only while this lambda.
  macroBuffer = llvm::MemoryBuffer::getMemBufferCopy({utf8Start, length});
});
  • or, the lambda receives a size and returns a buffer pointer of the size (i.e. factory) 
    swift_ASTGen_evaluateMacro( ..., [&](size_t utf8Length) {
  macroBuffer = llvm::WritableMemoryBuffer::getNewUninitMemBuffer(utf8Length + 1, bufferIdentifier);
  return macroBuffer->getBufferStart();
  // the caller initializes the buffer.
});

So the size that allocates the memory has the responsibility to free it.

But I guess there's no way to pass C++ lambda to Swift, at this point?

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We can pass through a C function pointer and a context pointer, which would eliminate a copy and not have a malloc/free pair across languages.


// Create a source file to hold the macro buffer. This is automatically
// registered with the enclosing module.
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