[RISCV] Codegen support for atomic operations on RV32I

This patch adds lowering for atomic fences and relies on AtomicExpandPass to
lower atomic loads/stores, atomic rmw, and cmpxchg to __atomic_* libcalls.

test/CodeGen/RISCV/atomic-* are modelled on the exhaustive
test/CodeGen/PPC/atomics-regression.ll, and will prove more useful once RV32A
codegen support is introduced.

Fence mappings are taken from table A.6 in the current draft of version 2.3 of
the RISC-V Instruction Set Manual, which incorporates the memory model changes
and definitions contributed by the RISC-V Memory Consistency Model task group.

Differential Revision: https://reviews.llvm.org/D47587

llvm-svn: 334590

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/RISCVTargetMachine.cpp b/llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
index d025e82984b..29f6bead42f 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
@@ -75,6 +75,7 @@ public:
     return getTM<RISCVTargetMachine>();
   }
 
+  void addIRPasses() override;
   bool addInstSelector() override;
   void addPreEmitPass() override;
 };
@@ -84,6 +85,11 @@ TargetPassConfig *RISCVTargetMachine::createPassConfig(PassManagerBase &PM) {
   return new RISCVPassConfig(*this, PM);
 }
 
+void RISCVPassConfig::addIRPasses() {
+  addPass(createAtomicExpandPass());
+  TargetPassConfig::addIRPasses();
+}
+
 bool RISCVPassConfig::addInstSelector() {
   addPass(createRISCVISelDag(getRISCVTargetMachine()));