[RISCV] Define FeatureRelax and shouldForceRelocation for RISCV linker relaxation

1. Deine FeatureRelax to enable/disable linker relaxation.

2. Define shouldForceRelocation to preserve relocation types even if the fixup
   can be resolved when linker relaxation enabled. This is necessary for
   correctness as offsets may change during relaxation.

Differential Revision: https://reviews.llvm.org/D46674

llvm-svn: 332318

diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
index 65425e4..9c4ca81 100644 (file)
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
@@ -43,6 +43,14 @@ public:
   std::unique_ptr<MCObjectWriter>
   createObjectWriter(raw_pwrite_stream &OS) const override;
 
+  // If linker relaxation is enabled, always emit relocations even if the fixup
+  // can be resolved. This is necessary for correctness as offsets may change
+  // during relaxation.
+  bool shouldForceRelocation(const MCAssembler &Asm, const MCFixup &Fixup,
+                             const MCValue &Target) override {
+    return STI.getFeatureBits()[RISCV::FeatureRelax];
+  }
+
   bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
                             const MCRelaxableFragment *DF,
                             const MCAsmLayout &Layout) const override;

diff --git a/llvm/lib/Target/RISCV/RISCV.td b/llvm/lib/Target/RISCV/RISCV.td
index 3e80d74..281378c 100644 (file)
--- a/llvm/lib/Target/RISCV/RISCV.td
+++ b/llvm/lib/Target/RISCV/RISCV.td
@@ -55,6 +55,10 @@ def IsRV32 : Predicate<"!Subtarget->is64Bit()">,
 def RV64           : HwMode<"+64bit">;
 def RV32           : HwMode<"-64bit">;
 
+def FeatureRelax
+    : SubtargetFeature<"relax", "EnableLinkerRelax", "true",
+                       "Enable Linker relaxation.">;
+
 //===----------------------------------------------------------------------===//
 // Registers, calling conventions, instruction descriptions.
 //===----------------------------------------------------------------------===//

diff --git a/llvm/lib/Target/RISCV/RISCVSubtarget.h b/llvm/lib/Target/RISCV/RISCVSubtarget.h
index 928ba58..0e09391 100644 (file)
--- a/llvm/lib/Target/RISCV/RISCVSubtarget.h
+++ b/llvm/lib/Target/RISCV/RISCVSubtarget.h
@@ -36,6 +36,7 @@ class RISCVSubtarget : public RISCVGenSubtargetInfo {
   bool HasStdExtD = false;
   bool HasStdExtC = false;
   bool HasRV64 = false;
+  bool EnableLinkerRelax = false;
   unsigned XLen = 32;
   MVT XLenVT = MVT::i32;
   RISCVFrameLowering FrameLowering;
@@ -77,6 +78,7 @@ public:
   bool hasStdExtD() const { return HasStdExtD; }
   bool hasStdExtC() const { return HasStdExtC; }
   bool is64Bit() const { return HasRV64; }
+  bool enableLinkerRelax() const { return EnableLinkerRelax; }
   MVT getXLenVT() const { return XLenVT; }
   unsigned getXLen() const { return XLen; }
 };