[llvm] [MC,X86] De-virtualize emitPrefix (PR #97008)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Fangrui Song (MaskRay)

<details>
<summary>Changes</summary>

and remove x86-specific emitPrefix from the generic MCCodeEmitter.


---
Full diff: https://github.com/llvm/llvm-project/pull/97008.diff


4 Files Affected:

- (modified) llvm/include/llvm/MC/MCCodeEmitter.h (-6) 
- (modified) llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp (+1-1) 
- (modified) llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp (+6-1) 
- (modified) llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h (+4) 


``````````diff
diff --git a/llvm/include/llvm/MC/MCCodeEmitter.h b/llvm/include/llvm/MC/MCCodeEmitter.h
index e4f4b27816bb3..ceb16c9b4da78 100644
--- a/llvm/include/llvm/MC/MCCodeEmitter.h
+++ b/llvm/include/llvm/MC/MCCodeEmitter.h
@@ -30,12 +30,6 @@ class MCCodeEmitter {
   /// Lifetime management
   virtual void reset() {}
 
-  /// Append the prefixes of given instruction to the code buffer.
-  ///
-  /// \param Inst a single low-level machine instruction.
-  /// \param CB code buffer
-  virtual void emitPrefix(const MCInst &Inst, SmallVectorImpl<char> &CB,
-                          const MCSubtargetInfo &STI) const {}
   /// Encode the given \p Inst to bytes and append to \p CB.
   virtual void encodeInstruction(const MCInst &Inst, SmallVectorImpl<char> &CB,
                                  SmallVectorImpl<MCFixup> &Fixups,
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 4567daeb5c4a0..372de5c18ac2b 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -788,7 +788,7 @@ bool X86AsmBackend::padInstructionViaPrefix(MCRelaxableFragment &RF,
   const unsigned MaxPossiblePad = std::min(15 - OldSize, RemainingSize);
   const unsigned RemainingPrefixSize = [&]() -> unsigned {
     SmallString<15> Code;
-    Emitter.emitPrefix(RF.getInst(), Code, STI);
+    X86_MC::emitPrefix(Emitter, RF.getInst(), Code, STI);
     assert(Code.size() < 15 && "The number of prefixes must be less than 15.");
 
     // TODO: It turns out we need a decent amount of plumbing for the target
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
index 72219c136c7e1..3cd0af0c7f546 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
@@ -344,7 +344,7 @@ class X86MCCodeEmitter : public MCCodeEmitter {
   ~X86MCCodeEmitter() override = default;
 
   void emitPrefix(const MCInst &MI, SmallVectorImpl<char> &CB,
-                  const MCSubtargetInfo &STI) const override;
+                  const MCSubtargetInfo &STI) const;
 
   void encodeInstruction(const MCInst &MI, SmallVectorImpl<char> &CB,
                          SmallVectorImpl<MCFixup> &Fixups,
@@ -1531,6 +1531,11 @@ void X86MCCodeEmitter::emitPrefix(const MCInst &MI, SmallVectorImpl<char> &CB,
   emitPrefixImpl(CurOp, MI, STI, CB);
 }
 
+void X86_MC::emitPrefix(MCCodeEmitter &MCE, const MCInst &MI,
+                        SmallVectorImpl<char> &CB, const MCSubtargetInfo &STI) {
+  static_cast<X86MCCodeEmitter &>(MCE).emitPrefix(MI, CB, STI);
+}
+
 void X86MCCodeEmitter::encodeInstruction(const MCInst &MI,
                                          SmallVectorImpl<char> &CB,
                                          SmallVectorImpl<MCFixup> &Fixups,
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h b/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h
index 9e68d0c670329..96a7823b04ad8 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h
@@ -13,6 +13,7 @@
 #ifndef LLVM_LIB_TARGET_X86_MCTARGETDESC_X86MCTARGETDESC_H
 #define LLVM_LIB_TARGET_X86_MCTARGETDESC_X86MCTARGETDESC_H
 
+#include "llvm/ADT/SmallVector.h"
 #include <memory>
 #include <string>
 
@@ -93,6 +94,9 @@ MCSubtargetInfo *createX86MCSubtargetInfo(const Triple &TT, StringRef CPU,
 
 void emitInstruction(MCObjectStreamer &, const MCInst &Inst,
                      const MCSubtargetInfo &STI);
+
+void emitPrefix(MCCodeEmitter &MCE, const MCInst &MI, SmallVectorImpl<char> &CB,
+                const MCSubtargetInfo &STI);
 }
 
 MCCodeEmitter *createX86MCCodeEmitter(const MCInstrInfo &MCII,

``````````

</details>


https://github.com/llvm/llvm-project/pull/97008