Add an atomic lowering pass

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110113 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 161 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/CMakeLists.txt b/lib/Transforms/Scalar/CMakeLists.txt
index 1a3b10cc9b..c8028c2470 100644
--- a/lib/Transforms/Scalar/CMakeLists.txt
+++ b/lib/Transforms/Scalar/CMakeLists.txt
@@ -17,6 +17,7 @@ add_llvm_library(LLVMScalarOpts
   LoopStrengthReduce.cpp
   LoopUnrollPass.cpp
   LoopUnswitch.cpp
+  LowerAtomic.cpp
   MemCpyOptimizer.cpp
   Reassociate.cpp
   Reg2Mem.cpp
diff --git a/lib/Transforms/Scalar/LowerAtomic.cpp b/lib/Transforms/Scalar/LowerAtomic.cpp
new file mode 100644
index 0000000000..11f52570e1
--- /dev/null
+++ b/lib/Transforms/Scalar/LowerAtomic.cpp
@@ -0,0 +1,160 @@
+//===- LowerAtomic.cpp - Lower atomic intrinsics --------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass lowers atomic intrinsics to non-atomic form for use in a known
+// non-preemptible environment.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "loweratomic"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/Function.h"
+#include "llvm/Instruction.h"
+#include "llvm/Instructions.h"
+#include "llvm/Intrinsics.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/IRBuilder.h"
+
+using namespace llvm;
+
+namespace {
+
+bool LowerAtomicIntrinsic(CallInst *CI) {
+  IRBuilder<> Builder(CI->getParent(), CI);
+
+  Function *Callee = CI->getCalledFunction();
+  if (!Callee)
+    return false;
+
+  unsigned IID = Callee->getIntrinsicID();
+  switch (IID) {
+  case Intrinsic::memory_barrier:
+    break;
+
+  case Intrinsic::atomic_load_add:
+  case Intrinsic::atomic_load_sub:
+  case Intrinsic::atomic_load_and:
+  case Intrinsic::atomic_load_nand:
+  case Intrinsic::atomic_load_or:
+  case Intrinsic::atomic_load_xor:
+  case Intrinsic::atomic_load_max:
+  case Intrinsic::atomic_load_min:
+  case Intrinsic::atomic_load_umax:
+  case Intrinsic::atomic_load_umin: {
+    Value *Ptr = CI->getArgOperand(0);
+    Value *Delta = CI->getArgOperand(1);
+
+    LoadInst *Orig = Builder.CreateLoad(Ptr);
+    Value *Res;
+    switch (IID) {
+      case Intrinsic::atomic_load_add:
+        Res = Builder.CreateAdd(Orig, Delta);
+        break;
+      case Intrinsic::atomic_load_sub:
+        Res = Builder.CreateSub(Orig, Delta);
+        break;
+      case Intrinsic::atomic_load_and:
+        Res = Builder.CreateAnd(Orig, Delta);
+        break;
+      case Intrinsic::atomic_load_nand:
+        Res = Builder.CreateNot(Builder.CreateAnd(Orig, Delta));
+        break;
+      case Intrinsic::atomic_load_or:
+        Res = Builder.CreateOr(Orig, Delta);
+        break;
+      case Intrinsic::atomic_load_xor:
+        Res = Builder.CreateXor(Orig, Delta);
+        break;
+      case Intrinsic::atomic_load_max:
+        Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Delta),
+                                   Delta,
+                                   Orig);
+        break;
+      case Intrinsic::atomic_load_min:
+        Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Delta),
+                                   Orig,
+                                   Delta);
+        break;
+      case Intrinsic::atomic_load_umax:
+        Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Delta),
+                                   Delta,
+                                   Orig);
+        break;
+      case Intrinsic::atomic_load_umin:
+        Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Delta),
+                                   Orig,
+                                   Delta);
+        break;
+      default: assert(0 && "Unrecognized atomic modify operation");
+    }
+    Builder.CreateStore(Res, Ptr);
+
+    CI->replaceAllUsesWith(Orig);
+    break;
+  }
+
+  case Intrinsic::atomic_swap: {
+    Value *Ptr = CI->getArgOperand(0);
+    Value *Val = CI->getArgOperand(1);
+
+    LoadInst *Orig = Builder.CreateLoad(Ptr);
+    Builder.CreateStore(Val, Ptr);
+
+    CI->replaceAllUsesWith(Orig);
+    break;
+  }
+
+  case Intrinsic::atomic_cmp_swap: {
+    Value *Ptr = CI->getArgOperand(0);
+    Value *Cmp = CI->getArgOperand(1);
+    Value *Val = CI->getArgOperand(2);
+
+    LoadInst *Orig = Builder.CreateLoad(Ptr);
+    Value *Equal = Builder.CreateICmpEQ(Orig, Cmp);
+    Value *Res = Builder.CreateSelect(Equal, Val, Orig);
+    Builder.CreateStore(Res, Ptr);
+
+    CI->replaceAllUsesWith(Orig);
+    break;
+  }
+
+  default:
+    return false;
+  }
+
+  assert(CI->use_empty() &&
+         "Lowering should have eliminated any uses of the intrinsic call!");
+  CI->eraseFromParent();
+
+  return true;
+}
+
+struct LowerAtomic : public BasicBlockPass {
+  static char ID;
+  LowerAtomic() : BasicBlockPass(&ID) {}
+  bool runOnBasicBlock(BasicBlock &BB) {
+    bool Changed = false;
+    for (BasicBlock::iterator DI = BB.begin(), DE = BB.end(); DI != DE; ) {
+      Instruction *Inst = DI++;
+      if (CallInst *CI = dyn_cast<CallInst>(Inst))
+        Changed |= LowerAtomicIntrinsic(CI);
+    }
+    return Changed;
+  }
+
+};
+
+}
+
+char LowerAtomic::ID = 0;
+static RegisterPass<LowerAtomic>
+X("loweratomic", "Lower atomic intrinsics to non-atomic form");
+
+Pass *llvm::createLowerAtomicPass() { return new LowerAtomic(); }