[Intrinsic] Signed and Unsigned Saturation Subtraction Intirnsics

Add an intrinsic that takes 2 integers and perform saturation subtraction on
them.

This is a part of implementing fixed point arithmetic in clang where some of
the more complex operations will be implemented as intrinsics.

Differential Revision: https://reviews.llvm.org/D53783

llvm-svn: 345512

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 3434f24db91..ddead1d93a5 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5783,6 +5783,18 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
     setValue(&I, DAG.getNode(ISD::UADDSAT, sdl, Op1.getValueType(), Op1, Op2));
     return nullptr;
   }
+  case Intrinsic::ssub_sat: {
+    SDValue Op1 = getValue(I.getArgOperand(0));
+    SDValue Op2 = getValue(I.getArgOperand(1));
+    setValue(&I, DAG.getNode(ISD::SSUBSAT, sdl, Op1.getValueType(), Op1, Op2));
+    return nullptr;
+  }
+  case Intrinsic::usub_sat: {
+    SDValue Op1 = getValue(I.getArgOperand(0));
+    SDValue Op2 = getValue(I.getArgOperand(1));
+    setValue(&I, DAG.getNode(ISD::USUBSAT, sdl, Op1.getValueType(), Op1, Op2));
+    return nullptr;
+  }
   case Intrinsic::stacksave: {
     SDValue Op = getRoot();
     Res = DAG.getNode(