[llvm] Parse CFI instructions to create SFrame FREs (PR #155496)

[James Henderson via llvm-commits]

================
@@ -88,13 +189,96 @@ class SFrameEmitterImpl {
                .has_value());
     FDEs.reserve(Streamer.getDwarfFrameInfos().size());
     SFrameABI = *Streamer.getContext().getObjectFileInfo()->getSFrameABIArch();
+    switch (SFrameABI) {
+    case ABI::AArch64EndianBig:
+    case ABI::AArch64EndianLittle:
+      SPReg = 31;
+      RAReg = 29;
+      FPReg = 30;
+      break;
+    case ABI::AMD64EndianLittle:
+      SPReg = 7;
+      // RARegister untracked in this abi. Value chosen to match
+      // MCDwarfFrameInfo constructor.
+      RAReg = static_cast<unsigned>(INT_MAX);
+      FPReg = 6;
+      break;
+    }
+
     FDESubSectionStart = Streamer.getContext().createTempSymbol();
     FRESubSectionStart = Streamer.getContext().createTempSymbol();
     FRESubSectionEnd = Streamer.getContext().createTempSymbol();
   }
 
-  void BuildSFDE(const MCDwarfFrameInfo &DF) {
-    FDEs.emplace_back(DF, Streamer.getContext().createTempSymbol());
+  bool atSameLocation(const MCSymbol *Left, const MCSymbol *Right) {
+    return Left != nullptr && Right != nullptr &&
+           Left->getFragment() == Right->getFragment() &&
+           Left->getOffset() == Right->getOffset();
+  }
+
+  bool equalIgnoringLocation(const SFrameFRE &Left, const SFrameFRE &Right) {
+    return Left.CFAOffset == Right.CFAOffset &&
+           Left.FPOffset == Right.FPOffset && Left.RAOffset == Right.RAOffset &&
+           Left.FromFP == Right.FromFP && Left.CFARegSet == Right.CFARegSet;
+  }
+
+  void buildSFDE(const MCDwarfFrameInfo &DF) {
+    bool Valid = true;
+    SFrameFDE FDE(DF, Streamer.getContext().createTempSymbol());
+    // This would have been set via ".cfi_return_column", but
+    // MCObjectStreamer doesn't emit an MCCFIInstruction for that. It just
+    // sets the DF.RAReg.
+    // FIXME: This also prevents providing a proper location for the error.
+    // LLVM doesn't change the return column itself, so this was
+    // hand-written assembly.
+    if (DF.RAReg != RAReg) {
+      Streamer.getContext().reportWarning(
+          SMLoc(), "Non-default RA register in .cfi_return_column " +
----------------
jh7370 wrote:

Nit: `non-default` to conform with LLVM warning style guide.

https://github.com/llvm/llvm-project/pull/155496