[ARM,MVE] Use VMOV.{S8,S16} for sign-extended extractelement.

MVE includes instructions that extract an 8- or 16-bit lane from a
vector and sign-extend it into the output 32-bit GPR. `ARMInstrMVE.td`
already included isel patterns to select those instructions in
response to the `ARMISD::VGETLANEs` selection-DAG node type. But
`ARMISD::VGETLANEs` was never actually generated, because the code
that creates it was conditioned on NEON only.

It's an easy fix to enable the same code for integer MVE, and now IR
that sign-extends the result of an extractelement (whether explicitly
or as part of the function call ABI) will use `vmov.s8` instead of
`vmov.u8` followed by `sxtb`.

Reviewers: SjoerdMeijer, dmgreen, ostannard

Subscribers: kristof.beyls, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70132

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 9f3389cb790..c395a4feea7 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -13843,11 +13843,12 @@ static SDValue PerformExtendCombine(SDNode *N, SelectionDAG &DAG,
                                     const ARMSubtarget *ST) {
   SDValue N0 = N->getOperand(0);
 
-  // Check for sign- and zero-extensions of vector extract operations of 8-
-  // and 16-bit vector elements.  NEON supports these directly.  They are
+  // Check for sign- and zero-extensions of vector extract operations of 8- and
+  // 16-bit vector elements. NEON and MVE support these directly. They are
   // handled during DAG combining because type legalization will promote them
   // to 32-bit types and it is messy to recognize the operations after that.
-  if (ST->hasNEON() && N0.getOpcode() == ISD::EXTRACT_VECTOR_ELT) {
+  if ((ST->hasNEON() || ST->hasMVEIntegerOps()) &&
+      N0.getOpcode() == ISD::EXTRACT_VECTOR_ELT) {
     SDValue Vec = N0.getOperand(0);
     SDValue Lane = N0.getOperand(1);
     EVT VT = N->getValueType(0);