[llvm] [GlobalISel] Refactor extractParts() (PR #75223)

[David Green via llvm-commits]

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@@ -335,53 +336,45 @@ void applyExtAddvToUdotAddv(MachineInstr &MI, MachineRegisterInfo &MRI,
     SmallVector<Register, 4> Ext1UnmergeReg;
     SmallVector<Register, 4> Ext2UnmergeReg;
     if (SrcTy.getNumElements() % 16 != 0) {
-      // Unmerge source to v8i8, append a new v8i8 of 0s and the merge to v16s
-      SmallVector<Register, 4> PadUnmergeDstReg1;
-      SmallVector<Register, 4> PadUnmergeDstReg2;
-      unsigned NumOfVec = SrcTy.getNumElements() / 8;
-
-      // Unmerge the source to v8i8
-      MachineInstr *PadUnmerge1 =
-          Builder.buildUnmerge(LLT::fixed_vector(8, 8), Ext1SrcReg);
-      MachineInstr *PadUnmerge2 =
-          Builder.buildUnmerge(LLT::fixed_vector(8, 8), Ext2SrcReg);
-      for (unsigned i = 0; i < NumOfVec; i++) {
-        PadUnmergeDstReg1.push_back(PadUnmerge1->getOperand(i).getReg());
-        PadUnmergeDstReg2.push_back(PadUnmerge2->getOperand(i).getReg());
+      SmallVector<Register, 1> Leftover1;
+      SmallVector<Register, 1> Leftover2;
+
+      // Split the elements into v16i8 and v8i8
+      LLT MainTy = LLT::fixed_vector(16, 8);
+      LLT LeftoverTy1, LeftoverTy2;
+      if ((!extractParts(Ext1SrcReg, MRI.getType(Ext1SrcReg), MainTy,
+                         LeftoverTy1, Ext1UnmergeReg, Leftover1, Builder,
+                         MRI)) ||
+          (!extractParts(Ext2SrcReg, MRI.getType(Ext2SrcReg), MainTy,
+                         LeftoverTy2, Ext2UnmergeReg, Leftover2, Builder,
+                         MRI))) {
+        llvm_unreachable("Unable to split this vector properly");
       }
 
-      // Pad the vectors with a v8i8 constant of 0s
+      // Pad the leftover v8i8 vector with register of 0s of type v8i8
       MachineInstr *v8Zeroes =
           Builder.buildConstant(LLT::fixed_vector(8, 8), 0);
-      PadUnmergeDstReg1.push_back(v8Zeroes->getOperand(0).getReg());
-      PadUnmergeDstReg2.push_back(v8Zeroes->getOperand(0).getReg());
-
-      // Merge them all back to v16i8
-      NumOfVec = (NumOfVec + 1) / 2;
-      for (unsigned i = 0; i < NumOfVec; i++) {
-        Ext1UnmergeReg.push_back(
-            Builder
-                .buildMergeLikeInstr(
-                    LLT::fixed_vector(16, 8),
-                    {PadUnmergeDstReg1[i * 2], PadUnmergeDstReg1[(i * 2) + 1]})
-                .getReg(0));
-        Ext2UnmergeReg.push_back(
-            Builder
-                .buildMergeLikeInstr(
-                    LLT::fixed_vector(16, 8),
-                    {PadUnmergeDstReg2[i * 2], PadUnmergeDstReg2[(i * 2) + 1]})
-                .getReg(0));
-      }
+      Leftover1.push_back(v8Zeroes->getOperand(0).getReg());
+      Leftover2.push_back(v8Zeroes->getOperand(0).getReg());
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davemgreen wrote:

I think here we will know that Leftover.size() == 1, so we don't need to add the zeros to the array we can use it directly.

https://github.com/llvm/llvm-project/pull/75223