[MC] Always encode instruction into SmallVector

All users of MCCodeEmitter::encodeInstruction use a raw_svector_ostream
to encode the instruction into a SmallVector. The raw_ostream however
incurs some overhead for the actual encoding.

This change allows an MCCodeEmitter to directly emit an instruction into
a SmallVector without using a raw_ostream and therefore allow for
performance improvments in encoding. A default path that uses existing
raw_ostream implementations is provided.

Reviewed By: MaskRay, Amir

Differential Revision: https://reviews.llvm.org/D145791

3 files changed, 3 insertions, 6 deletions

diff --git a/bolt/include/bolt/Core/BinaryContext.h b/bolt/include/bolt/Core/BinaryContext.h
index 26b8a64af3dc..7e2d4d6e045c 100644
--- a/bolt/include/bolt/Core/BinaryContext.h
+++ b/bolt/include/bolt/Core/BinaryContext.h
@@ -1227,8 +1227,7 @@ public:
       Emitter = this->MCE.get();
     SmallString<256> Code;
     SmallVector<MCFixup, 4> Fixups;
-    raw_svector_ostream VecOS(Code);
-    Emitter->encodeInstruction(Inst, VecOS, Fixups, *STI);
+    Emitter->encodeInstruction(Inst, Code, Fixups, *STI);
     return Code.size();
   }
 
diff --git a/bolt/lib/Core/BinaryContext.cpp b/bolt/lib/Core/BinaryContext.cpp
index 09f59f7ad632..6a9e35e04eec 100644
--- a/bolt/lib/Core/BinaryContext.cpp
+++ b/bolt/lib/Core/BinaryContext.cpp
@@ -2289,9 +2289,8 @@ bool BinaryContext::validateInstructionEncoding(
 
   SmallString<256> Code;
   SmallVector<MCFixup, 4> Fixups;
-  raw_svector_ostream VecOS(Code);
 
-  MCE->encodeInstruction(Inst, VecOS, Fixups, *STI);
+  MCE->encodeInstruction(Inst, Code, Fixups, *STI);
   auto OutputSequence = ArrayRef<uint8_t>((uint8_t *)Code.data(), Code.size());
   if (InputSequence != OutputSequence) {
     if (opts::Verbosity > 1) {
diff --git a/bolt/lib/Core/BinaryFunction.cpp b/bolt/lib/Core/BinaryFunction.cpp
index 69ebd12bd0db..14a10be62d20 100644
--- a/bolt/lib/Core/BinaryFunction.cpp
+++ b/bolt/lib/Core/BinaryFunction.cpp
@@ -1536,8 +1536,7 @@ bool BinaryFunction::scanExternalRefs() {
     // Emit the instruction using temp emitter and generate relocations.
     SmallString<256> Code;
     SmallVector<MCFixup, 4> Fixups;
-    raw_svector_ostream VecOS(Code);
-    Emitter.MCE->encodeInstruction(Instruction, VecOS, Fixups, *BC.STI);
+    Emitter.MCE->encodeInstruction(Instruction, Code, Fixups, *BC.STI);
 
     // Create relocation for every fixup.
     for (const MCFixup &Fixup : Fixups) {