Revert "[GlobalISel] Add scalar widening for G_MERGE_VALUES destination"

This reverts commit 0a37163d1d855a2db41e1f46ddbc3f4570bd7ca6.

Reason: Broke the sanitizer msan bots. More details are available in the
original Phabricator review: https://reviews.llvm.org/D106814.
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 38b2b23..c1e0d25 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -1418,7 +1418,11 @@
 }
 
 LegalizerHelper::LegalizeResult
-LegalizerHelper::widenScalarSrcMergeValues(MachineInstr &MI, LLT WideTy) {
+LegalizerHelper::widenScalarMergeValues(MachineInstr &MI, unsigned TypeIdx,
+                                        LLT WideTy) {
+  if (TypeIdx != 1)
+    return UnableToLegalize;
+
   Register DstReg = MI.getOperand(0).getReg();
   LLT DstTy = MRI.getType(DstReg);
   if (DstTy.isVector())
@@ -1535,44 +1539,6 @@
   return Legalized;
 }
 
-LegalizerHelper::LegalizeResult
-LegalizerHelper::widenScalarDstMergeValues(MachineInstr &MI, LLT WideTy) {
-  // Disallow for vectors and pointers. Not sure about what to do with pointers.
-  LLT DstTy = MRI.getType(MI.getOperand(0).getReg());
-  if (!DstTy.isScalar())
-    return UnableToLegalize;
-  LLT SrcTy = MRI.getType(MI.getOperand(1).getReg());
-  const int DstSize = DstTy.getSizeInBits();
-  const int SrcSize = SrcTy.getSizeInBits();
-  const int WideSize = WideTy.getSizeInBits();
-  // If WideSize = DstSize + K * SrcSize then we can get WideSize by padding
-  // with K undef elements.
-  //
-  //    dst = G_MERGE_VALUES elt1, elt2, ..., eltN
-  // -> wide_dst = G_MERGE_VALUES elt1, elt2, ... eltN, pad1, pad2, ... padK
-  int Difference = WideSize - DstSize;
-  if ((Difference) % SrcSize != 0)
-    return UnableToLegalize;
-  int NumPadEltsToAdd = Difference / SrcSize;
-  assert(NumPadEltsToAdd && "Expected to add at least one element?");
-  MachineFunction &MF = *MI.getMF();
-  for (int I = 0; I < NumPadEltsToAdd; ++I) {
-    auto PadElt = MIRBuilder.buildUndef(SrcTy);
-    MI.addOperand(
-        MF, MachineOperand::CreateReg(PadElt.getReg(0), /*isDef = */ false));
-  }
-  widenScalarDst(MI, WideTy, 0);
-  return Legalized;
-}
-
-LegalizerHelper::LegalizeResult
-LegalizerHelper::widenScalarMergeValues(MachineInstr &MI, unsigned TypeIdx,
-                                        LLT WideTy) {
-  if (TypeIdx == 0)
-    return widenScalarDstMergeValues(MI, WideTy);
-  return widenScalarSrcMergeValues(MI, WideTy);
-}
-
 Register LegalizerHelper::widenWithUnmerge(LLT WideTy, Register OrigReg) {
   Register WideReg = MRI.createGenericVirtualRegister(WideTy);
   LLT OrigTy = MRI.getType(OrigReg);