[llvm] DAG: Handle equal size element build_vector promotion (PR #76213)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

This will allow promotion of bf16 to i16 vectors in a future patch.

---
Full diff: https://github.com/llvm/llvm-project/pull/76213.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp (+7-3) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index a483b8028fda9e..4e317062cec497 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -4908,7 +4908,9 @@ void SelectionDAGLegalize::ConvertNodeToLibcall(SDNode *Node) {
 static MVT getPromotedVectorElementType(const TargetLowering &TLI,
                                         MVT EltVT, MVT NewEltVT) {
   unsigned OldEltsPerNewElt = EltVT.getSizeInBits() / NewEltVT.getSizeInBits();
-  MVT MidVT = MVT::getVectorVT(NewEltVT, OldEltsPerNewElt);
+  MVT MidVT = OldEltsPerNewElt == 1
+                  ? NewEltVT
+                  : MVT::getVectorVT(NewEltVT, OldEltsPerNewElt);
   assert(TLI.isTypeLegal(MidVT) && "unexpected");
   return MidVT;
 }
@@ -5395,7 +5397,7 @@ void SelectionDAGLegalize::PromoteNode(SDNode *Node) {
 
     assert(NVT.isVector() && OVT.getSizeInBits() == NVT.getSizeInBits() &&
            "Invalid promote type for build_vector");
-    assert(NewEltVT.bitsLT(EltVT) && "not handled");
+    assert(NewEltVT.bitsLE(EltVT) && "not handled");
 
     MVT MidVT = getPromotedVectorElementType(TLI, EltVT, NewEltVT);
 
@@ -5406,7 +5408,9 @@ void SelectionDAGLegalize::PromoteNode(SDNode *Node) {
     }
 
     SDLoc SL(Node);
-    SDValue Concat = DAG.getNode(ISD::CONCAT_VECTORS, SL, NVT, NewOps);
+    SDValue Concat =
+        DAG.getNode(MidVT == NewEltVT ? ISD::BUILD_VECTOR : ISD::CONCAT_VECTORS,
+                    SL, NVT, NewOps);
     SDValue CvtVec = DAG.getNode(ISD::BITCAST, SL, OVT, Concat);
     Results.push_back(CvtVec);
     break;

``````````

</details>


https://github.com/llvm/llvm-project/pull/76213