[llvm] [AMDGPU] SelectionDAG support for vector type set 0 to multiple sgpr64 (PR #128017)

[Matt Arsenault via llvm-commits]

================
@@ -634,6 +634,61 @@ void AMDGPUDAGToDAGISel::Select(SDNode *N) {
   case ISD::BUILD_VECTOR: {
     EVT VT = N->getValueType(0);
     unsigned NumVectorElts = VT.getVectorNumElements();
+
+    auto IsSplatAllZeros = [this](SDNode *N) -> bool {
+      if (ISD::isConstantSplatVectorAllZeros(N))
+        return true;
+
+      // Types may have legalized by stripping the 16 bit multi-element vector
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arsenm wrote:

Even if they don't splat 0

https://github.com/llvm/llvm-project/pull/128017