[SelectionDAG] Initial support for FSHL/FSHR funnel shift opcodes (PR39467)

This is an initial patch to add a minimum level of support for funnel shifts to the SelectionDAG and to begin wiring it up to the X86 SHLD/SHRD instructions.

Some partial legalization code has been added to handle the case for 'SlowSHLD' where we want to expand instead and I've added a few DAG combines so we don't get regressions from the existing DAG builder expansion code.

Differential Revision: https://reviews.llvm.org/D54698

llvm-svn: 348353

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index a6a8ebe1a47..d0d748f3841 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5751,6 +5751,12 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
     SDValue Zero = DAG.getConstant(0, sdl, VT);
     SDValue ShAmt = DAG.getNode(ISD::UREM, sdl, VT, Z, BitWidthC);
 
+    auto FunnelOpcode = IsFSHL ? ISD::FSHL : ISD::FSHR;
+    if (TLI.isOperationLegalOrCustom(FunnelOpcode, VT)) {
+      setValue(&I, DAG.getNode(FunnelOpcode, sdl, VT, X, Y, Z));
+      return nullptr;
+    }
+
     // When X == Y, this is rotate. If the data type has a power-of-2 size, we
     // avoid the select that is necessary in the general case to filter out
     // the 0-shift possibility that leads to UB.