[Intrinsic] Add fixed point division intrinsics.

Summary:
This patch adds intrinsics and ISelDAG nodes for
signed and unsigned fixed-point division:

  llvm.sdiv.fix.*
  llvm.udiv.fix.*

These intrinsics perform scaled division on two
integers or vectors of integers. They are required
for the implementation of the Embedded-C fixed-point
arithmetic in Clang.

Patch by: ebevhan

Reviewers: bjope, leonardchan, efriedma, craig.topper

Reviewed By: craig.topper

Subscribers: Ka-Ka, ilya, hiraditya, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70007

1 files changed, 21 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index c41aef34b53..80ac8b95e4e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -1129,7 +1129,9 @@ void SelectionDAGLegalize::LegalizeOp(SDNode *Node) {
   case ISD::SMULFIX:
   case ISD::SMULFIXSAT:
   case ISD::UMULFIX:
-  case ISD::UMULFIXSAT: {
+  case ISD::UMULFIXSAT:
+  case ISD::SDIVFIX:
+  case ISD::UDIVFIX: {
     unsigned Scale = Node->getConstantOperandVal(2);
     Action = TLI.getFixedPointOperationAction(Node->getOpcode(),
                                               Node->getValueType(0), Scale);
@@ -3417,6 +3419,24 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
   case ISD::UMULFIXSAT:
     Results.push_back(TLI.expandFixedPointMul(Node, DAG));
     break;
+  case ISD::SDIVFIX:
+  case ISD::UDIVFIX:
+    if (SDValue V = TLI.expandFixedPointDiv(Node->getOpcode(), SDLoc(Node),
+                                            Node->getOperand(0),
+                                            Node->getOperand(1),
+                                            Node->getConstantOperandVal(2),
+                                            DAG)) {
+      Results.push_back(V);
+      break;
+    }
+    // FIXME: We might want to retry here with a wider type if we fail, if that
+    // type is legal.
+    // FIXME: Technically, so long as we only have sdivfixes where BW+Scale is
+    // <= 128 (which is the case for all of the default Embedded-C types),
+    // we will only get here with types and scales that we could always expand
+    // if we were allowed to generate libcalls to division functions of illegal
+    // type. But we cannot do that.
+    llvm_unreachable("Cannot expand DIVFIX!");
   case ISD::ADDCARRY:
   case ISD::SUBCARRY: {
     SDValue LHS = Node->getOperand(0);