MachineIRBuilder: Add buildMergeValues. NFC

Add a `buildMergeValues` method that unconditionally builds a
G_MERGE_VALUES instruction, as opposed to `buildMergeLikeInstr` which
may decide on a different opcode based on the input types.

I haven't audited all the uses of `buildMergeLikeInstr` to see if they
can be replaced with `buildMergeValues`, but I did find a couple of
obvious ones where we check that we're merging scalars right before
calling `buildMerge`.

This is a follow-up suggested in https://reviews.llvm.org/D140964

Differential Revision: https://reviews.llvm.org/D141373

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp b/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp
index a6148a6..9100e06 100644
--- a/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp
@@ -597,6 +597,16 @@ MachineInstrBuilder MachineIRBuilder::buildUndef(const DstOp &Res) {
   return buildInstr(TargetOpcode::G_IMPLICIT_DEF, {Res}, {});
 }
 
+MachineInstrBuilder MachineIRBuilder::buildMergeValues(const DstOp &Res,
+                                                       ArrayRef<Register> Ops) {
+  // Unfortunately to convert from ArrayRef<LLT> to ArrayRef<SrcOp>,
+  // we need some temporary storage for the DstOp objects. Here we use a
+  // sufficiently large SmallVector to not go through the heap.
+  SmallVector<SrcOp, 8> TmpVec(Ops.begin(), Ops.end());
+  assert(TmpVec.size() > 1);
+  return buildInstr(TargetOpcode::G_MERGE_VALUES, Res, TmpVec);
+}
+
 MachineInstrBuilder
 MachineIRBuilder::buildMergeLikeInstr(const DstOp &Res,
                                       ArrayRef<Register> Ops) {