[RISCV] Implement codegen for cmpxchg on RV32IA

Utilise a similar ('late') lowering strategy to D47882. The changes to 
AtomicExpandPass allow this strategy to be utilised by other targets which 
implement shouldExpandAtomicCmpXchgInIR.

All cmpxchg are lowered as 'strong' currently and failure ordering is ignored. 
This is conservative but correct.

Differential Revision: https://reviews.llvm.org/D48131

llvm-svn: 347914

1 files changed, 32 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/AtomicExpandPass.cpp b/llvm/lib/CodeGen/AtomicExpandPass.cpp
index c1b98794015..95581c09dd1 100644
--- a/llvm/lib/CodeGen/AtomicExpandPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandPass.cpp
@@ -91,6 +91,7 @@ namespace {
     AtomicRMWInst *widenPartwordAtomicRMW(AtomicRMWInst *AI);
     void expandPartwordCmpXchg(AtomicCmpXchgInst *I);
     void expandAtomicRMWToMaskedIntrinsic(AtomicRMWInst *AI);
+    void expandAtomicCmpXchgToMaskedIntrinsic(AtomicCmpXchgInst *CI);
 
     AtomicCmpXchgInst *convertCmpXchgToIntegerType(AtomicCmpXchgInst *CI);
     static Value *insertRMWCmpXchgLoop(
@@ -944,6 +945,35 @@ void AtomicExpand::expandAtomicRMWToMaskedIntrinsic(AtomicRMWInst *AI) {
   AI->eraseFromParent();
 }
 
+void AtomicExpand::expandAtomicCmpXchgToMaskedIntrinsic(AtomicCmpXchgInst *CI) {
+  IRBuilder<> Builder(CI);
+
+  PartwordMaskValues PMV = createMaskInstrs(
+      Builder, CI, CI->getCompareOperand()->getType(), CI->getPointerOperand(),
+      TLI->getMinCmpXchgSizeInBits() / 8);
+
+  Value *CmpVal_Shifted = Builder.CreateShl(
+      Builder.CreateZExt(CI->getCompareOperand(), PMV.WordType), PMV.ShiftAmt,
+      "CmpVal_Shifted");
+  Value *NewVal_Shifted = Builder.CreateShl(
+      Builder.CreateZExt(CI->getNewValOperand(), PMV.WordType), PMV.ShiftAmt,
+      "NewVal_Shifted");
+  Value *OldVal = TLI->emitMaskedAtomicCmpXchgIntrinsic(
+      Builder, CI, PMV.AlignedAddr, CmpVal_Shifted, NewVal_Shifted, PMV.Mask,
+      CI->getSuccessOrdering());
+  Value *FinalOldVal = Builder.CreateTrunc(
+      Builder.CreateLShr(OldVal, PMV.ShiftAmt), PMV.ValueType);
+
+  Value *Res = UndefValue::get(CI->getType());
+  Res = Builder.CreateInsertValue(Res, FinalOldVal, 0);
+  Value *Success = Builder.CreateICmpEQ(
+      CmpVal_Shifted, Builder.CreateAnd(OldVal, PMV.Mask), "Success");
+  Res = Builder.CreateInsertValue(Res, Success, 1);
+
+  CI->replaceAllUsesWith(Res);
+  CI->eraseFromParent();
+}
+
 Value *AtomicExpand::insertRMWLLSCLoop(
     IRBuilder<> &Builder, Type *ResultTy, Value *Addr,
     AtomicOrdering MemOpOrder,
@@ -1366,8 +1396,8 @@ bool AtomicExpand::tryExpandAtomicCmpXchg(AtomicCmpXchgInst *CI) {
     return expandAtomicCmpXchg(CI);
   }
   case TargetLoweringBase::AtomicExpansionKind::MaskedIntrinsic:
-    llvm_unreachable(
-        "MaskedIntrinsic expansion of cmpxhg not yet implemented");
+    expandAtomicCmpXchgToMaskedIntrinsic(CI);
+    return true;
   }
 }