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

[Pavel Labath via llvm-commits]

================
@@ -109,91 +107,81 @@ class SFrameEmitterImpl {
   MCSymbol *FRESubSectionStart;
   MCSymbol *FRESubSectionEnd;
 
-
-  bool setCfaRegister(SFrameFDE &FDE, SFrameFRE &FRE, const MCCFIInstruction &I) {
+  bool setCFARegister(SFrameFRE &FRE, const MCCFIInstruction &I) {
     if (I.getRegister() == SPReg) {
-      FRE.CfaRegSet = true;
+      FRE.CFARegSet = true;
       FRE.FromFP = false;
       return true;
-    } else if (I.getRegister() == FPReg) {
-      FRE.CfaRegSet = true;
+    }
+    if (I.getRegister() == FPReg) {
+      FRE.CFARegSet = true;
       FRE.FromFP = true;
       return true;
     }
     Streamer.getContext().reportWarning(
         I.getLoc(), "Canonical Frame Address not in stack- or frame-pointer. "
                     "Omitting SFrame unwind info for this function.");
-    FDE.Invalid = true;
     return false;
   }
 
-  bool isCfaRegisterSet(SFrameFDE &FDE, SFrameFRE &FRE,
-                        const MCCFIInstruction &I) {
-    if (FRE.CfaRegSet)
-      return true;
-
-    Streamer.getContext().reportWarning(
-        I.getLoc(), "Adjusting CFA offset without a base register. "
-                    "Omitting SFrame unwind info for this function.");
-    FDE.Invalid = true;
-    return false;
+  bool setCFAOffset(SFrameFRE &FRE, const SMLoc &Loc, size_t Offset) {
+    if (!FRE.CFARegSet) {
+      Streamer.getContext().reportWarning(
+          Loc, "Adjusting CFA offset without a base register. "
+               "Omitting SFrame unwind info for this function.");
+      return false;
+    }
+    FRE.CFAOffset = Offset;
+    return true;
   }
 
   // Add the effects of CFI to the current FDE, creating a new FRE when
   // necessary.
-  void handleCFI(SFrameFDE &FDE, SFrameFRE &FRE, const MCCFIInstruction &CFI) {
+  bool handleCFI(SFrameFDE &FDE, SFrameFRE &FRE, const MCCFIInstruction &CFI) {
     switch (CFI.getOperation()) {
     case MCCFIInstruction::OpDefCfaRegister:
-      setCfaRegister(FDE, FRE, CFI);
-      return;
+      return setCFARegister(FRE, CFI);
     case MCCFIInstruction::OpDefCfa:
     case MCCFIInstruction::OpLLVMDefAspaceCfa:
-      if (!setCfaRegister(FDE, FRE, CFI))
-        return;
-      FRE.CfaOffset = CFI.getOffset();
-      return;
+      if (!setCFARegister(FRE, CFI))
+        return false;
+      setCFAOffset(FRE, CFI.getLoc(), CFI.getOffset());
+      return true;
----------------
labath wrote:

Should this be:

```suggestion
      return setCFAOffset(FRE, CFI.getLoc(), CFI.getOffset());
```

I guess the difference is that if this was the only error, the code would still go on to produce a (broken) FDE entry. 

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