Lower @llvm.experimental.deoptimize as a noreturn call

While preserving the return value for @llvm.experimental.deoptimize at
the IR level is useful during mid-level optimization, doing so at the
machine instruction level requires generating some extra code and a
return that is non-ideal.  This change has LLVM lower

```
  %val = call @llvm.experimental.deoptimize
  ret %val
```

to effectively

```
  call @__llvm_deoptimize()
  unreachable
```

instead.

llvm-svn: 265502

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 91c0a04a3b4..f6b4262ffd7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1377,6 +1377,18 @@ void SelectionDAGBuilder::visitRet(const ReturnInst &I) {
   SmallVector<ISD::OutputArg, 8> Outs;
   SmallVector<SDValue, 8> OutVals;
 
+  // Calls to @llvm.experimental.deoptimize don't generate a return value, so
+  // lower
+  //
+  //   %val = call <ty> @llvm.experimental.deoptimize()
+  //   ret <ty> %val
+  //
+  // differently.
+  if (I.getParent()->getTerminatingDeoptimizeCall()) {
+    LowerDeoptimizingReturn();
+    return;
+  }
+
   if (!FuncInfo.CanLowerReturn) {
     unsigned DemoteReg = FuncInfo.DemoteRegister;
     const Function *F = I.getParent()->getParent();