Update Reactor/LLVMJIT for RISC-V.

This CL fixes 3 RISC-V issues:
* JIT Linking on RISC-V is only supported with
  ObjectLinkingLayer.
* jitTargetMachineBuilder.getFeatures() on RISC-V does
  not return the RISC-V CPU extensions, so they are
  manually added.
  Note that these CPU extensions will be widely supported.
  Android for instance will require at least RV64GC, where
  the "G" stands for the +m +a +f +d extensions, and the C
  stands for the +c extension.
* setCodeModel needs to be set to Medium on RISC-V.

Bug: b/273278430
Test: succesfully ran graphics tests in risc-v cuttlefish
with swiftshader running in the guest.

Change-Id: I9081be16450b9bd4d2b1e67e5777578fb1a688fc
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/71768
Commit-Queue: Jean-François Geyelin <jif@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Tested-by: Jean-François Geyelin <jif@google.com>

src/Reactor/LLVMJIT.cpp

diff --git a/src/Reactor/LLVMJIT.cpp b/src/Reactor/LLVMJIT.cpp
index fad747a..11c7bab 100644
--- a/src/Reactor/LLVMJIT.cpp
+++ b/src/Reactor/LLVMJIT.cpp
@@ -26,9 +26,23 @@
     __pragma(warning(disable : 4146))  // unary minus operator applied to unsigned type, result still unsigned
 #endif
 
+// See https://groups.google.com/g/llvm-dev/c/CAE7Va57h2c/m/74ITeXFEAQAJ
+// for information about `RTDyldObjectLinkingLayer` vs `ObjectLinkingLayer`.
+// On RISC-V, only `ObjectLinkingLayer` is supported.
+#if defined(__riscv)
+#define USE_LEGACY_OBJECT_LINKING_LAYER 0
+#else
+#define USE_LEGACY_OBJECT_LINKING_LAYER 1
+#endif
+
 #include "llvm/ExecutionEngine/Orc/CompileUtils.h"
 #include "llvm/ExecutionEngine/Orc/IRCompileLayer.h"
+
+#if USE_LEGACY_OBJECT_LINKING_LAYER
 #include "llvm/ExecutionEngine/Orc/RTDyldObjectLinkingLayer.h"
+#else
+#include "llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h"
+#endif
 #include "llvm/ExecutionEngine/SectionMemoryManager.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Verifier.h"
@@ -216,13 +230,28 @@
 #else
 		(void)ok;  // getHostCPUFeatures always returns false on other platforms
 #endif
-
 		for(auto &feature : cpuFeatures)
 		{
 			jitTargetMachineBuilder.getFeatures().AddFeature(feature.first(), feature.second);
 		}
 
 #if LLVM_VERSION_MAJOR >= 11 /* TODO(b/165000222): Unconditional after LLVM 11 upgrade */
+
+#if defined(__riscv) && __riscv_xlen == 64
+		// jitTargetMachineBuilder.getFeatures() on RISC-V does
+		// not return the RISC-V CPU extensions, so they are
+		// manually added.
+		jitTargetMachineBuilder.getFeatures().AddFeature("+m");
+		jitTargetMachineBuilder.getFeatures().AddFeature("+a");
+		jitTargetMachineBuilder.getFeatures().AddFeature("+f");
+		jitTargetMachineBuilder.getFeatures().AddFeature("+d");
+		jitTargetMachineBuilder.getFeatures().AddFeature("+c");
+		// The default code model is "Small".
+		// On RISC-V, using the default code model results in an
+		// "Unsupported riscv relocation" error.
+		jitTargetMachineBuilder.setCodeModel(llvm::CodeModel::Medium);
+#endif
+
 		jitTargetMachineBuilder.setCPU(std::string(llvm::sys::getHostCPUName()));
 #else
 		jitTargetMachineBuilder.setCPU(llvm::sys::getHostCPUName());
@@ -746,9 +775,13 @@
 #if LLVM_VERSION_MAJOR >= 13
 	    , session(std::move(Unwrap(llvm::orc::SelfExecutorProcessControl::Create())))
 #endif
+#if USE_LEGACY_OBJECT_LINKING_LAYER
 	    , objectLayer(session, [this]() {
 		    return std::make_unique<llvm::SectionMemoryManager>(&memoryMapper);
 	    })
+#else
+	    , objectLayer(session, llvm::cantFail(llvm::jitlink::InProcessMemoryManager::Create()))
+#endif
 	    , addresses(count)
 	{
 		bool fatalCompileIssue = false;
@@ -861,7 +894,11 @@
 	std::string name;
 	llvm::orc::ExecutionSession session;
 	MemoryMapper memoryMapper;
+#if USE_LEGACY_OBJECT_LINKING_LAYER
 	llvm::orc::RTDyldObjectLinkingLayer objectLayer;
+#else
+	llvm::orc::ObjectLinkingLayer objectLayer;
+#endif
 	std::vector<const void *> addresses;
 };