[llvm] fb13be0 - MC: Generalize evaluateTargetFixup

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2025-07-05T00:19:48-07:00
New Revision: fb13be06e18d3e19f3380fc46ff4009918beb19f

URL: https://github.com/llvm/llvm-project/commit/fb13be06e18d3e19f3380fc46ff4009918beb19f
DIFF: https://github.com/llvm/llvm-project/commit/fb13be06e18d3e19f3380fc46ff4009918beb19f.diff

LOG: MC: Generalize evaluateTargetFixup

Generalize evaluateTargetFixup to be called by all targets,
making FKF_IsTarget unneeded.

Next: Update targets that use FKF_IsAlignedDownTo32Bits to define
`evaluateFixup` and remove FKF_IsAlignedDownTo32Bits from the generic
code.

Added: 
    

Modified: 
    llvm/include/llvm/MC/MCAsmBackend.h
    llvm/lib/MC/MCAssembler.cpp
    llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
    llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h
    llvm/test/MC/RISCV/Relocations/mc-dump.s

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/MC/MCAsmBackend.h b/llvm/include/llvm/MC/MCAsmBackend.h
index 2b591032c2985..fae7fba8e8274 100644
--- a/llvm/include/llvm/MC/MCAsmBackend.h
+++ b/llvm/include/llvm/MC/MCAsmBackend.h
@@ -131,9 +131,12 @@ class LLVM_ABI MCAsmBackend {
     return false;
   }
 
-  virtual bool evaluateTargetFixup(const MCFixup &Fixup, const MCValue &Target,
-                                   uint64_t &Value) {
-    llvm_unreachable("Need to implement hook if target has custom fixups");
+  // Evaluate a fixup, returning std::nullopt to use default handling for
+  // `Value` and `IsResolved`. Otherwise, returns `IsResolved` with the
+  // expectation that the hook updates `Value`.
+  virtual std::optional<bool> evaluateFixup(MCFixup &Fixup, MCValue &Target,
+                                            uint64_t &Value) {
+    return {};
   }
 
   void maybeAddReloc(const MCFragment &, const MCFixup &, const MCValue &,

diff  --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 64fc0a8f25f43..e02fcb1e77f92 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -163,8 +163,8 @@ bool MCAssembler::evaluateFixup(const MCFragment &F, MCFixup &Fixup,
 
   unsigned FixupFlags = getBackend().getFixupKindInfo(Fixup.getKind()).Flags;
   bool IsResolved = false;
-  if (FixupFlags & MCFixupKindInfo::FKF_IsTarget) {
-    IsResolved = getBackend().evaluateTargetFixup(Fixup, Target, Value);
+  if (auto State = getBackend().evaluateFixup(Fixup, Target, Value)) {
+    IsResolved = *State;
   } else {
     const MCSymbol *Add = Target.getAddSym();
     const MCSymbol *Sub = Target.getSubSym();

diff  --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
index 7f7bbfa91fc5b..ce0d030031cdb 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
@@ -70,8 +70,8 @@ MCFixupKindInfo RISCVAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"fixup_riscv_12_i", 20, 12, 0},
       {"fixup_riscv_lo12_s", 0, 32, 0},
       {"fixup_riscv_pcrel_hi20", 12, 20, 0},
-      {"fixup_riscv_pcrel_lo12_i", 20, 12, MCFixupKindInfo::FKF_IsTarget},
-      {"fixup_riscv_pcrel_lo12_s", 0, 32, MCFixupKindInfo::FKF_IsTarget},
+      {"fixup_riscv_pcrel_lo12_i", 20, 12, 0},
+      {"fixup_riscv_pcrel_lo12_s", 0, 32, 0},
       {"fixup_riscv_jal", 12, 20, 0},
       {"fixup_riscv_branch", 0, 32, 0},
       {"fixup_riscv_rvc_jump", 2, 11, 0},
@@ -655,15 +655,16 @@ static const MCFixup *getPCRelHiFixup(const MCSpecifierExpr &Expr,
   return nullptr;
 }
 
-bool RISCVAsmBackend::evaluateTargetFixup(const MCFixup &Fixup,
-                                          const MCValue &Target,
-                                          uint64_t &Value) {
+std::optional<bool> RISCVAsmBackend::evaluateFixup(MCFixup &Fixup,
+                                                   MCValue &Target,
+                                                   uint64_t &Value) {
   const MCFixup *AUIPCFixup;
   const MCFragment *AUIPCDF;
   MCValue AUIPCTarget;
   switch (Fixup.getTargetKind()) {
   default:
-    llvm_unreachable("Unexpected fixup kind!");
+    // Use default handling for `Value` and `IsResolved`.
+    return {};
   case RISCV::fixup_riscv_pcrel_lo12_i:
   case RISCV::fixup_riscv_pcrel_lo12_s: {
     AUIPCFixup =

diff  --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h
index d98361ea5857f..292cacdbd45af 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h
@@ -47,8 +47,8 @@ class RISCVAsmBackend : public MCAsmBackend {
   bool shouldInsertFixupForCodeAlign(MCAssembler &Asm,
                                      MCAlignFragment &AF) override;
 
-  bool evaluateTargetFixup(const MCFixup &Fixup, const MCValue &Target,
-                           uint64_t &Value) override;
+  std::optional<bool> evaluateFixup(MCFixup &Fixup, MCValue &Target,
+                                    uint64_t &Value) override;
 
   bool addReloc(const MCFragment &, const MCFixup &, const MCValue &,
                 uint64_t &FixedValue, bool IsResolved);

diff  --git a/llvm/test/MC/RISCV/Relocations/mc-dump.s b/llvm/test/MC/RISCV/Relocations/mc-dump.s
index 2ebd249fcf49b..98205925da1cd 100644
--- a/llvm/test/MC/RISCV/Relocations/mc-dump.s
+++ b/llvm/test/MC/RISCV/Relocations/mc-dump.s
@@ -7,7 +7,7 @@
 # CHECK-NEXT:  Symbol @0 .text
 # CHECK-NEXT:0 Align Align:4 Value:0 ValueSize:1 MaxBytesToEmit:4 Nops
 # CHECK-NEXT:0 Data LinkerRelaxable Size:8 [97,00,00,00,e7,80,00,00]
-# CHECK-NEXT:  Fixup @0 Value:specifier(19,ext) Kind:4026
+# CHECK-NEXT:  Fixup @0 Value:specifier(19,ext) Kind:4022
 # CHECK-NEXT:  Symbol @0 $x
 # CHECK-NEXT:8 Align Align:8 Value:0 ValueSize:1 MaxBytesToEmit:8 Nops
 # CHECK-NEXT:12 Data Size:4 [13,05,30,00]