[CodeGen] More bits for calling convention

[Xinglong]

Summary

According to https://reveiws.llvm.org/D13826, bitcode use 10 bits to represent calling convention ID, but for clang codegen, we only have 8 bits. so if we use a calling convention ID greater than 255, clang will truncate it, and bitcode will get an error calling convention ID. Single 32-bit unit is broken, so here we use 16 bits.

[Xinglong]

ping

[rjmccall]

clang/include/clang/CodeGen/CGFunctionInfo.h

562

At some point, these bit-fields fit into a single 32-bit unit. There's currently 33 bits, so that hasn't been true for a while, and we might as well make all three of these fields 16 bits.

It doesn't look like there's a good opportunity to pack the struct because we're at an odd number of 32-bit chunks overall, so that'll do for now.

[Xinglong]

Some patch broken the single 32-bit unit, so here use 16 bits is better.

[Xinglong]

clang/include/clang/CodeGen/CGFunctionInfo.h

562

Yes, 32-bit unit is broken, here use 16 bits is better and llvm backend need a patch to align to 16 bits.

[Xinglong]

rebase

[rjmccall]

LGTM

clang/include/clang/CodeGen/CGFunctionInfo.h

class CGFunctionInfo final
     : public llvm::FoldingSetNode,
       private llvm::TrailingObjects<CGFunctionInfo, CGFunctionInfoArgInfo,
                                     FunctionProtoType::ExtParameterInfo> {
   typedef CGFunctionInfoArgInfo ArgInfo;
   typedef FunctionProtoType::ExtParameterInfo ExtParameterInfo;
 
   /// The LLVM::CallingConv to use for this function (as specified by the
   /// user).
-  unsigned CallingConvention : 8;
+  unsigned CallingConvention : 16;
 
   /// The LLVM::CallingConv to actually use for this function, which may
   /// depend on the ABI.
-  unsigned EffectiveCallingConvention : 8;
+  unsigned EffectiveCallingConvention : 16;
 
   /// The clang::CallingConv that this was originally created with.
-  unsigned ASTCallingConvention : 6;
+  unsigned ASTCallingConvention : 16;
 
   /// Whether this is an instance method.
   unsigned InstanceMethod : 1;
 
   /// Whether this is a chain call.
   unsigned ChainCall : 1;
 
   /// Whether this function is a CMSE nonsecure call