Replace SimpleCompiler to avoid a copy and createObjectFile (#59486)

Replace the call to orc::SimpleCompiler::operator() with equivalent code
that doesn't unnecessarily parse the object file again (if it would have
failed, we're going to find out later anyway). This also lets us make
the MemoryBuffer name unique and avoid copying it in
JuliaOJIT::addObjectFile.

REF:
https://github.com/JuliaLang/llvm-project/blob/85122d41d6783e828412f9a1d0f7c771e2a38acc/llvm/lib/ExecutionEngine/Orc/CompileUtils.cpp#L38-L67

Author: xal-0

src/jitlayers.cpp

@@ -1609,10 +1609,33 @@ namespace {
                 PoolIdx = jl_options.opt_level;
             }
             assert(PoolIdx < N && "Invalid optimization level for compiler!");
-            return orc::SimpleCompiler(****TMs[PoolIdx])(M);
+
+            auto TM = **TMs[PoolIdx];
+            if (M.getDataLayout().isDefault())
+                M.setDataLayout((*TM)->createDataLayout());
+
+            SmallVector<char, 0> ObjBufferSV;
+            {
+                raw_svector_ostream ObjStream(ObjBufferSV);
+                legacy::PassManager PM;
+                MCContext *Ctx;
+                if ((*TM)->addPassesToEmitMC(PM, Ctx, ObjStream))
+                    return make_error<StringError>("Target does not support MC emission",
+                                                   inconvertibleErrorCode());
+                PM.run(M);
+            }
+
+            // OrcJIT requires that all modules / files have unique names:
+            // https://llvm.org/doxygen/namespacellvm_1_1orc.html#a1f5a1bc60c220cdccbab0f26b2a425e1
+            auto name = (M.getModuleIdentifier() + "-jitted-" +
+                         Twine(jl_atomic_fetch_add_relaxed(&bufcounter, 1)))
+                            .str();
+            return std::make_unique<SmallVectorMemoryBuffer>(std::move(ObjBufferSV), name,
+                                                             false);
         }
 
         std::array<std::unique_ptr<JuliaOJIT::ResourcePool<std::unique_ptr<TargetMachine>>>, N> TMs;
+        _Atomic(size_t) bufcounter{0};
     };
 }
 
@@ -2133,11 +2156,6 @@ Error JuliaOJIT::addExternalModule(orc::JITDylib &JD, orc::ThreadSafeModule TSM,
 
 Error JuliaOJIT::addObjectFile(orc::JITDylib &JD, std::unique_ptr<MemoryBuffer> Obj) {
     assert(Obj && "Can not add null object");
-    // OrcJIT requires that all modules / files have unique names:
-    // https://llvm.org/doxygen/namespacellvm_1_1orc.html#a1f5a1bc60c220cdccbab0f26b2a425e1
-    // so we have to force a copy here
-    std::string Name = ("jitted-" + Twine(jl_atomic_fetch_add_relaxed(&jitcounter, 1))).str();
-    Obj = Obj->getMemBufferCopy(Obj->getBuffer(), Name);
     return ObjectLayer.add(JD.getDefaultResourceTracker(), std::move(Obj));
 }