[llvm] [LoongArch] Allow delayed decision for ADD/SUB relocations (PR #72960)

[Jinyang He via llvm-commits]

MQ-mengqing wrote:

Follow RISCV 1df5ea29, we can fix it by the diff. I'll add some test cases. 

BTW, add tests is messy for this RELAX series patches. I reduced the correlation between patches so that patches could be reviewed earlier. Commit in progress may be affected by a previous commit. #72961 is an example where I need to re-modify the test case after #72960 is merged.

```diff
diff --git a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
index 6d8ef1bf96cb..9c080aba2c96 100644
--- a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
+++ b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
@@ -173,6 +173,7 @@ bool LoongArchAsmBackend::shouldForceRelocation(const MCAssembler &Asm,
   case FK_Data_2:
   case FK_Data_4:
   case FK_Data_8:
+  case FK_Data_leb128:
     return !Target.isAbsolute();
   }
 }
@@ -202,9 +203,25 @@ getRelocPairForSize(unsigned Size) {
     return std::make_pair(
         MCFixupKind(FirstLiteralRelocationKind + ELF::R_LARCH_ADD64),
         MCFixupKind(FirstLiteralRelocationKind + ELF::R_LARCH_SUB64));
+  case 128:
+    return std::make_pair(
+        MCFixupKind(FirstLiteralRelocationKind + ELF::R_LARCH_ADD_ULEB128),
+        MCFixupKind(FirstLiteralRelocationKind + ELF::R_LARCH_SUB_ULEB128));
   }
 }
 
+bool LoongArchAsmBackend::relaxLEB128(MCLEBFragment &LF, MCAsmLayout &Layout,
+                                      int64_t &Value) const {
+  if (LF.isSigned())
+    return false;
+  const MCExpr &Expr = LF.getValue();
+//  if (ULEB128Reloc) {
+    LF.getFixups().push_back(
+        MCFixup::create(0, &Expr, FK_Data_leb128, Expr.getLoc()));
+//  }
+  return Expr.evaluateKnownAbsolute(Value, Layout);
+}
+
 bool LoongArchAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
                                        const MCSubtargetInfo *STI) const {
   // We mostly follow binutils' convention here: align to 4-byte boundary with a
@@ -255,6 +272,9 @@ bool LoongArchAsmBackend::handleAddSubRelocations(const MCAsmLayout &Layout,
   case llvm::FK_Data_8:
     FK = getRelocPairForSize(64);
     break;
+  case llvm::FK_Data_leb128:
+    FK = getRelocPairForSize(128);
+    break;
   default:
     llvm_unreachable("unsupported fixup size");
   }
diff --git a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.h b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.h
index fef0e84600a7..238f5b931f58 100644
--- a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.h
+++ b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.h
@@ -66,6 +66,10 @@ public:
   void relaxInstruction(MCInst &Inst,
                         const MCSubtargetInfo &STI) const override {}
 
+
+  bool relaxLEB128(MCLEBFragment &LF, MCAsmLayout &Layout,
+                   int64_t &Value) const override;
+
   bool writeNopData(raw_ostream &OS, uint64_t Count,
                     const MCSubtargetInfo *STI) const override;
```

https://github.com/llvm/llvm-project/pull/72960