[llvm] a631af3 - Add EVT::changeVectorElementCount and MVT:changeVectorElementCount (#182266)

[via llvm-commits]

Author: Chaitanya Koparkar
Date: 2026-03-05T07:19:19-05:00
New Revision: a631af32c01bae47ff3ddf4645df2da96984ff09

URL: https://github.com/llvm/llvm-project/commit/a631af32c01bae47ff3ddf4645df2da96984ff09
DIFF: https://github.com/llvm/llvm-project/commit/a631af32c01bae47ff3ddf4645df2da96984ff09.diff

LOG: Add EVT::changeVectorElementCount and MVT:changeVectorElementCount (#182266)

Fixes #174584.

Added: 
    

Modified: 
    llvm/include/llvm/CodeGen/ValueTypes.h
    llvm/include/llvm/CodeGenTypes/MachineValueType.h
    llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/CodeGen/ValueTypes.h b/llvm/include/llvm/CodeGen/ValueTypes.h
index 3897cb8c18127..e8ce9ad8abfca 100644
--- a/llvm/include/llvm/CodeGen/ValueTypes.h
+++ b/llvm/include/llvm/CodeGen/ValueTypes.h
@@ -108,6 +108,18 @@ namespace llvm {
       return getVectorVT(Context, EltVT, getVectorElementCount());
     }
 
+    /// Return a VT for a vector type whose attributes match ourselves
+    /// with the exception of the element count that is chosen by the caller.
+    EVT changeVectorElementCount(LLVMContext &Context, ElementCount EC) const {
+      assert(isVector() && "Not a vector EVT!");
+      if (isSimple()) {
+        MVT M = getSimpleVT().changeVectorElementCount(EC);
+        if (M != MVT::INVALID_SIMPLE_VALUE_TYPE)
+          return M;
+      }
+      return getVectorVT(Context, getVectorElementType(), EC);
+    }
+
     /// Return a VT for a type whose attributes match ourselves with the
     /// exception of the element type that is chosen by the caller.
     EVT changeElementType(LLVMContext &Context, EVT EltVT) const {

diff  --git a/llvm/include/llvm/CodeGenTypes/MachineValueType.h b/llvm/include/llvm/CodeGenTypes/MachineValueType.h
index 08a9c85a213e0..99f0bb6aaac2d 100644
--- a/llvm/include/llvm/CodeGenTypes/MachineValueType.h
+++ b/llvm/include/llvm/CodeGenTypes/MachineValueType.h
@@ -217,6 +217,13 @@ namespace llvm {
       return VecTy;
     }
 
+    /// Return a VT for a vector type whose attributes match ourselves with
+    /// the exception of the element count that is chosen by the caller.
+    MVT changeVectorElementCount(ElementCount EC) const {
+      assert(isVector() && "Not a vector MVT!");
+      return MVT::getVectorVT(getVectorElementType(), EC);
+    }
+
     /// Return the type converted to an equivalently sized integer or vector
     /// with integer element type. Similar to changeVectorElementTypeToInteger,
     /// but also handles scalars.

diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 02490587330fd..d02e5f5b3b78f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -26192,9 +26192,8 @@ static SDValue combineConcatVectorOfCasts(SDNode *N, SelectionDAG &DAG) {
   // the operation support type parameter depends on the opcode. In addition,
   // check the other type in the cast to make sure this is really legal.
   EVT VT = N->getValueType(0);
-  EVT SrcEltVT = SrcVT.getVectorElementType();
   ElementCount NumElts = SrcVT.getVectorElementCount() * N->getNumOperands();
-  EVT ConcatSrcVT = EVT::getVectorVT(*DAG.getContext(), SrcEltVT, NumElts);
+  EVT ConcatSrcVT = SrcVT.changeVectorElementCount(*DAG.getContext(), NumElts);
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   switch (CastOpcode) {
   case ISD::SINT_TO_FP: