Fix SmallVector usage in SerailzeToHsaco (#71702)

Enable merging #71439 by removing a definitely-wrong usage of
std::unique_ptr<SmallVectorImpl<char>> as a return value with passing in
a SmallVectorImpl<char>&

Also change the following function to take ArrayRef<char> instead of
const SmalVectorImpl<char>& .

Author: krzysz00

mlir/lib/Dialect/GPU/Transforms/SerializeToHsaco.cpp

@@ -95,9 +95,9 @@ class SerializeToHsacoPass
   std::unique_ptr<std::vector<char>>
   serializeISA(const std::string &isa) override;
 
-  std::unique_ptr<SmallVectorImpl<char>> assembleIsa(const std::string &isa);
-  std::unique_ptr<std::vector<char>>
-  createHsaco(const SmallVectorImpl<char> &isaBinary);
+  LogicalResult assembleIsa(const std::string &isa,
+                            SmallVectorImpl<char> &result);
+  std::unique_ptr<std::vector<char>> createHsaco(ArrayRef<char> isaBinary);
 
   std::string getRocmPath();
 };
@@ -318,21 +318,18 @@ SerializeToHsacoPass::translateToLLVMIR(llvm::LLVMContext &llvmContext) {
   return ret;
 }
 
-std::unique_ptr<SmallVectorImpl<char>>
-SerializeToHsacoPass::assembleIsa(const std::string &isa) {
+LogicalResult SerializeToHsacoPass::assembleIsa(const std::string &isa,
+                                                SmallVectorImpl<char> &result) {
   auto loc = getOperation().getLoc();
 
-  SmallVector<char, 0> result;
   llvm::raw_svector_ostream os(result);
 
   llvm::Triple triple(llvm::Triple::normalize(this->triple));
   std::string error;
   const llvm::Target *target =
       llvm::TargetRegistry::lookupTarget(triple.normalize(), error);
-  if (!target) {
-    emitError(loc, Twine("failed to lookup target: ") + error);
-    return {};
-  }
+  if (!target)
+    return emitError(loc, Twine("failed to lookup target: ") + error);
 
   llvm::SourceMgr srcMgr;
   srcMgr.AddNewSourceBuffer(llvm::MemoryBuffer::getMemBuffer(isa), SMLoc());
@@ -373,19 +370,17 @@ SerializeToHsacoPass::assembleIsa(const std::string &isa) {
   std::unique_ptr<llvm::MCTargetAsmParser> tap(
       target->createMCAsmParser(*sti, *parser, *mcii, mcOptions));
 
-  if (!tap) {
-    emitError(loc, "assembler initialization error");
-    return {};
-  }
+  if (!tap)
+    return emitError(loc, "assembler initialization error");
 
   parser->setTargetParser(*tap);
   parser->Run(false);
 
-  return std::make_unique<SmallVector<char, 0>>(std::move(result));
+  return success();
 }
 
 std::unique_ptr<std::vector<char>>
-SerializeToHsacoPass::createHsaco(const SmallVectorImpl<char> &isaBinary) {
+SerializeToHsacoPass::createHsaco(ArrayRef<char> isaBinary) {
   auto loc = getOperation().getLoc();
 
   // Save the ISA binary to a temp file.
@@ -435,10 +430,10 @@ SerializeToHsacoPass::createHsaco(const SmallVectorImpl<char> &isaBinary) {
 
 std::unique_ptr<std::vector<char>>
 SerializeToHsacoPass::serializeISA(const std::string &isa) {
-  auto isaBinary = assembleIsa(isa);
-  if (!isaBinary)
+  SmallVector<char, 0> isaBinary;
+  if (failed(assembleIsa(isa, isaBinary)))
     return {};
-  return createHsaco(*isaBinary);
+  return createHsaco(isaBinary);
 }
 
 // Register pass to serialize GPU kernel functions to a HSACO binary annotation.