[llvm] 3fe6d27 - X86AsmBackend: Simplify isRightAfterData for the auto-pad feature

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2025-07-25T00:07:25-07:00
New Revision: 3fe6d276dc952b3b2b487cb67a999c3981cf9563

URL: https://github.com/llvm/llvm-project/commit/3fe6d276dc952b3b2b487cb67a999c3981cf9563
DIFF: https://github.com/llvm/llvm-project/commit/3fe6d276dc952b3b2b487cb67a999c3981cf9563.diff

LOG: X86AsmBackend: Simplify isRightAfterData for the auto-pad feature

Added: 
    

Modified: 
    llvm/include/llvm/MC/MCStreamer.h
    llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/MC/MCStreamer.h b/llvm/include/llvm/MC/MCStreamer.h
index dfaf3487e11a7..8ccce80ea7677 100644
--- a/llvm/include/llvm/MC/MCStreamer.h
+++ b/llvm/include/llvm/MC/MCStreamer.h
@@ -438,7 +438,7 @@ class LLVM_ABI MCStreamer {
     assert(!CurFrag || CurFrag->getKind() == MCFragment::FT_Data);
     return CurFrag;
   }
-  size_t getCurFragOffset() const { return getCurrentFragment()->Offset; }
+  size_t getCurFragSize() const { return getCurrentFragment()->getFixedSize(); }
   /// Save the current and previous section on the section stack.
   void pushSection() {
     SectionStack.push_back(

diff  --git a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index e213923ccf38e..7f9d474023a0d 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -388,36 +388,6 @@ static bool mayHaveInterruptDelaySlot(unsigned InstOpcode) {
   return false;
 }
 
-/// Check if the instruction to be emitted is right after any data.
-static bool
-isRightAfterData(MCFragment *CurrentFragment,
-                 const std::pair<MCFragment *, size_t> &PrevInstPosition) {
-  MCFragment *F = CurrentFragment;
-  // Since data is always emitted into a DataFragment, our check strategy is
-  // simple here.
-  //   - If the fragment is a DataFragment
-  //     - If it's empty (section start or data after align), return false.
-  //     - If it's not the fragment where the previous instruction is,
-  //       returns true.
-  //     - If it's the fragment holding the previous instruction but its
-  //       size changed since the previous instruction was emitted into
-  //       it, returns true.
-  //     - Otherwise returns false.
-  //   - If the fragment is not a DataFragment, returns false.
-  if (F->getKind() == MCFragment::FT_Data)
-    return F->getFixedSize() && (F != PrevInstPosition.first ||
-                                 F->getFixedSize() != PrevInstPosition.second);
-
-  return false;
-}
-
-/// \returns the fragment size if it has instructions, otherwise returns 0.
-static size_t getSizeForInstFragment(const MCFragment *F) {
-  if (!F || !F->hasInstructions())
-    return 0;
-  return F->getSize();
-}
-
 /// Return true if we can insert NOP or prefixes automatically before the
 /// the instruction to be emitted.
 bool X86AsmBackend::canPadInst(const MCInst &Inst, MCObjectStreamer &OS) const {
@@ -441,9 +411,11 @@ bool X86AsmBackend::canPadInst(const MCInst &Inst, MCObjectStreamer &OS) const {
     // semantic.
     return false;
 
-  if (isRightAfterData(OS.getCurrentFragment(), PrevInstPosition))
-    // If this instruction follows any data, there is no clear
-    // instruction boundary, inserting a nop/prefix would change semantic.
+  // If this instruction follows any data, there is no clear instruction
+  // boundary, inserting a nop/prefix would change semantic.
+  auto Offset = OS.getCurFragSize();
+  if (Offset && (OS.getCurrentFragment() != PrevInstPosition.first ||
+                 Offset != PrevInstPosition.second))
     return false;
 
   return true;
@@ -552,7 +524,7 @@ void X86AsmBackend::emitInstructionEnd(MCObjectStreamer &OS,
   // Update PrevInstOpcode here, canPadInst() reads that.
   MCFragment *CF = OS.getCurrentFragment();
   PrevInstOpcode = Inst.getOpcode();
-  PrevInstPosition = std::make_pair(CF, getSizeForInstFragment(CF));
+  PrevInstPosition = std::make_pair(CF, OS.getCurFragSize());
 
   if (!canPadBranches(OS))
     return;