r205225 - MS ABI: mangleStringLiteral shouldn't rely on the host's endianness

[Reid Kleckner]

On Mon, Mar 31, 2014 at 10:18 AM, David Majnemer
<david.majnemer at gmail.com>wrote:

> Author: majnemer
> Date: Mon Mar 31 12:18:53 2014
> New Revision: 205225
>
> URL: http://llvm.org/viewvc/llvm-project?rev=205225&view=rev
> Log:
> MS ABI: mangleStringLiteral shouldn't rely on the host's endianness
>
> No test case is needed, the one in-tree is sufficient.  The build-bot
> never emailed me because something else had upset it.
>
> Modified:
>     cfe/trunk/lib/AST/MicrosoftMangle.cpp
>
> Modified: cfe/trunk/lib/AST/MicrosoftMangle.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/MicrosoftMangle.cpp?rev=205225&r1=205224&r2=205225&view=diff
>
> ==============================================================================
> --- cfe/trunk/lib/AST/MicrosoftMangle.cpp (original)
> +++ cfe/trunk/lib/AST/MicrosoftMangle.cpp Mon Mar 31 12:18:53 2014
> @@ -2385,9 +2385,39 @@ void MicrosoftMangleContextImpl::mangleS
>      }
>    };
>
> +  auto GetLittleEndianByte = [&Mangler, &SL](unsigned Index) {
>

Lambda nub question: can you capture SL by value since it never changes?


> +    unsigned CharByteWidth = SL->getCharByteWidth();
> +    uint32_t CodeUnit = SL->getCodeUnit(Index / CharByteWidth);
> +    if (CharByteWidth == 1) {
> +      return static_cast<char>(CodeUnit);
> +    } else if (CharByteWidth == 2) {
> +      if (Index % 2)
> +        return static_cast<char>((CodeUnit >> 8) & 0xff);
> +      else
> +        return static_cast<char>(CodeUnit & 0xff);
> +    } else {
> +      llvm_unreachable("unsupported CharByteWidth");
> +    }
> +  };
> +
> +  auto GetBigEndianByte = [&Mangler, &SL](unsigned Index) {
> +    unsigned CharByteWidth = SL->getCharByteWidth();
> +    uint32_t CodeUnit = SL->getCodeUnit(Index / CharByteWidth);
> +    if (CharByteWidth == 1) {
> +      return static_cast<char>(CodeUnit);
> +    } else if (CharByteWidth == 2) {
> +      if (Index % 2)
> +        return static_cast<char>(CodeUnit & 0xff);
> +      else
> +        return static_cast<char>((CodeUnit >> 8) & 0xff);
> +    } else {
> +      llvm_unreachable("unsupported CharByteWidth");
> +    }
> +  };
> +
>

This feels overly complex, but I haven't come up with any brilliant ideas
for simplifying it.  The best I can come up with is getting the bytes,
copying them, and endian swapping them appropriately.


>    // CRC all the bytes of the StringLiteral.
> -  for (char Byte : SL->getBytes())
> -    UpdateCRC(Byte);
> +  for (unsigned I = 0, E = SL->getByteLength(); I != E; ++I)
> +    UpdateCRC(GetLittleEndianByte(I));
>
>    // The NUL terminator byte(s) were not present earlier,
>    // we need to manually process those bytes into the CRC.
> @@ -2462,25 +2492,17 @@ void MicrosoftMangleContextImpl::mangleS
>      }
>    };
>
> -  auto MangleChar = [&Mangler, &MangleByte, &SL](uint32_t CodeUnit) {
> -    if (SL->getCharByteWidth() == 1) {
> -      MangleByte(static_cast<char>(CodeUnit));
> -    } else if (SL->getCharByteWidth() == 2) {
> -      MangleByte(static_cast<char>((CodeUnit >> 16) & 0xff));
> -      MangleByte(static_cast<char>(CodeUnit & 0xff));
> -    } else {
> -      llvm_unreachable("unsupported CharByteWidth");
> -    }
> -  };
> -
>    // Enforce our 32 character max.
>    unsigned NumCharsToMangle = std::min(32U, SL->getLength());
> -  for (unsigned i = 0; i < NumCharsToMangle; ++i)
> -    MangleChar(SL->getCodeUnit(i));
> +  for (unsigned I = 0, E = NumCharsToMangle * SL->getCharByteWidth(); I
> != E;
> +       ++I)
> +    MangleByte(GetBigEndianByte(I));
>
>    // Encode the NUL terminator if there is room.
>    if (NumCharsToMangle < 32)
> -    MangleChar(0);
> +    for (unsigned NullTerminator = 0; NullTerminator <
> SL->getCharByteWidth();
> +         ++NullTerminator)
> +      MangleByte(0);
>
>    Mangler.getStream() << '@';
>  }
>
>
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