[llvm] [SFrames] Emit and relax FREs (PR #158154)

[Fangrui Song via llvm-commits]

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@@ -33,10 +34,70 @@ struct SFrameFRE {
   size_t CFAOffset = 0;
   size_t FPOffset = 0;
   size_t RAOffset = 0;
-  bool FromFP = false;
+  FREInfo<endianness::native> Info;
   bool CFARegSet = false;
 
   SFrameFRE(const MCSymbol *Start) : Label(Start) {}
+
+  void emitOffset(MCObjectStreamer &S, FREOffset OffsetSize, size_t Offset) {
+    switch (OffsetSize) {
+    case (FREOffset::B1):
+      S.emitInt8(Offset);
+      return;
+    case (FREOffset::B2):
+      S.emitInt16(Offset);
+      return;
+    case (FREOffset::B4):
+      S.emitInt32(Offset);
+      return;
+    }
+  }
+
+  void emit(MCObjectStreamer &S, const MCSymbol *FuncBegin,
+            MCFragment *FDEFrag) {
+    S.emitSFrameCalculateFuncOffset(FuncBegin, Label, FDEFrag, SMLoc());
+
+    // fre_cfa_base_reg_id already set during parsing
+
+    // fre_offset_count
+    unsigned RegsTracked = 1; // always track the cfa.
+    if (FPOffset != 0)
+      RegsTracked++;
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MaskRay wrote:

LLVM coding style prefers pre-increment

https://github.com/llvm/llvm-project/pull/158154