[llvm] [AMDGPU] Legalize 64bit elements for BUILD_VECTOR on gfx942 (PR #145052)

[Chris Jackson via llvm-commits]

================
@@ -14372,6 +14379,18 @@ bool SITargetLowering::shouldExpandVectorDynExt(SDNode *N) const {
       EltSize, NumElem, Idx->isDivergent(), getSubtarget());
 }
 
+static unsigned getMappedVectorIndex(unsigned Idx, EVT From, EVT To) {
+  assert(From.isVector() && To.isVector() &&
+         "From and To types have to be vector types");
+  assert(From.getSizeInBits() == To.getSizeInBits() &&
+         "From and To vector types require the same size");
----------------
chrisjbris wrote:

```suggestion
         "Expected From and To vector types to have the same size in bits.");
```

https://github.com/llvm/llvm-project/pull/145052