[llvm] f15266e - [MC][ELF] Emit instructions directly into fragment (#94950)

[via llvm-commits]

Author: Alexis Engelke
Date: 2024-07-04T16:46:31+02:00
New Revision: f15266e9d5d87a291a515064f8f0dd5f0c412ed3

URL: https://github.com/llvm/llvm-project/commit/f15266e9d5d87a291a515064f8f0dd5f0c412ed3
DIFF: https://github.com/llvm/llvm-project/commit/f15266e9d5d87a291a515064f8f0dd5f0c412ed3.diff

LOG: [MC][ELF] Emit instructions directly into fragment (#94950)

Avoid needless copying of instructions and fixups and directly emit into
the fragment small vectors.

This (optionally, second commit) also removes the single use of the
MCCompactEncodedInstFragment to simplify code.

Added: 
    

Modified: 
    llvm/lib/MC/MCELFStreamer.cpp
    llvm/lib/MC/MCObjectStreamer.cpp
    llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCCodeEmitter.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/MC/MCELFStreamer.cpp b/llvm/lib/MC/MCELFStreamer.cpp
index e6e6b7d19dff4a..a30a64ba3df5e4 100644
--- a/llvm/lib/MC/MCELFStreamer.cpp
+++ b/llvm/lib/MC/MCELFStreamer.cpp
@@ -511,12 +511,6 @@ static void CheckBundleSubtargets(const MCSubtargetInfo *OldSTI,
 void MCELFStreamer::emitInstToData(const MCInst &Inst,
                                    const MCSubtargetInfo &STI) {
   MCAssembler &Assembler = getAssembler();
-  SmallVector<MCFixup, 4> Fixups;
-  SmallString<256> Code;
-  Assembler.getEmitter().encodeInstruction(Inst, Code, Fixups, STI);
-
-  for (auto &Fixup : Fixups)
-    fixSymbolsInTLSFixups(Fixup.getValue());
 
   // There are several possibilities here:
   //
@@ -526,9 +520,7 @@ void MCELFStreamer::emitInstToData(const MCInst &Inst,
   //
   // If bundling is enabled:
   // - If we're not in a bundle-locked group, emit the instruction into a
-  //   fragment of its own. If there are no fixups registered for the
-  //   instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
-  //   MCDataFragment.
+  //   fragment of its own.
   // - If we're in a bundle-locked group, append the instruction to the current
   //   data fragment because we want all the instructions in a group to get into
   //   the same fragment. Be careful not to do that for the first instruction in
@@ -542,16 +534,6 @@ void MCELFStreamer::emitInstToData(const MCInst &Inst,
       // The bundle-locking directive ensures this is a new data fragment.
       DF = cast<MCDataFragment>(getCurrentFragment());
       CheckBundleSubtargets(DF->getSubtargetInfo(), &STI);
-    } else if (!isBundleLocked() && Fixups.size() == 0) {
-      // Optimize memory usage by emitting the instruction to a
-      // MCCompactEncodedInstFragment when not in a bundle-locked group and
-      // there are no fixups registered.
-      MCCompactEncodedInstFragment *CEIF =
-          getContext().allocFragment<MCCompactEncodedInstFragment>();
-      insert(CEIF);
-      CEIF->getContents().append(Code.begin(), Code.end());
-      CEIF->setHasInstructions(STI);
-      return;
     } else {
       DF = getContext().allocFragment<MCDataFragment>();
       insert(DF);
@@ -571,17 +553,22 @@ void MCELFStreamer::emitInstToData(const MCInst &Inst,
     DF = getOrCreateDataFragment(&STI);
   }
 
-  // Add the fixups and data.
+  // Emit instruction directly into data fragment.
+  size_t FixupStartIndex = DF->getFixups().size();
+  size_t CodeOffset = DF->getContents().size();
+  Assembler.getEmitter().encodeInstruction(Inst, DF->getContents(),
+                                           DF->getFixups(), STI);
+
+  auto Fixups = MutableArrayRef(DF->getFixups()).slice(FixupStartIndex);
   for (auto &Fixup : Fixups) {
-    Fixup.setOffset(Fixup.getOffset() + DF->getContents().size());
-    DF->getFixups().push_back(Fixup);
+    Fixup.setOffset(Fixup.getOffset() + CodeOffset);
+    fixSymbolsInTLSFixups(Fixup.getValue());
   }
 
   DF->setHasInstructions(STI);
   if (!Fixups.empty() && Fixups.back().getTargetKind() ==
                              getAssembler().getBackend().RelaxFixupKind)
     DF->setLinkerRelaxable();
-  DF->getContents().append(Code.begin(), Code.end());
 }
 
 void MCELFStreamer::emitBundleAlignMode(Align Alignment) {

diff  --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index afe5da6e5fbb90..a72e34fe6fd334 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -393,10 +393,8 @@ void MCObjectStreamer::emitInstToFragment(const MCInst &Inst,
       getContext().allocFragment<MCRelaxableFragment>(Inst, STI);
   insert(IF);
 
-  SmallString<128> Code;
-  getAssembler().getEmitter().encodeInstruction(Inst, Code, IF->getFixups(),
-                                                STI);
-  IF->getContents().append(Code.begin(), Code.end());
+  getAssembler().getEmitter().encodeInstruction(Inst, IF->getContents(),
+                                                IF->getFixups(), STI);
 }
 
 #ifndef NDEBUG

diff  --git a/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCCodeEmitter.cpp b/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCCodeEmitter.cpp
index a6285a2ccf9d1a..b161eed95d6e26 100644
--- a/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCCodeEmitter.cpp
+++ b/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCCodeEmitter.cpp
@@ -172,7 +172,6 @@ uint64_t SystemZMCCodeEmitter::getImmOpValue(const MCInst &MI, unsigned OpNum,
     uint32_t BitOffset = MIBitSize - RawBitOffset - OpBitSize;
     Fixups.push_back(MCFixup::create(BitOffset >> 3, MO.getExpr(),
                                      (MCFixupKind)Kind, MI.getLoc()));
-    assert(Fixups.size() <= 2 && "More than two memory operands in MI?");
     return 0;
   }
   llvm_unreachable("Unexpected operand type!");