[llvm] [AArch64] Consider streaming mode in TTI interfaces for vectorization. (PR #96305)

[Paul Walker via llvm-commits]

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@@ -2162,19 +2162,20 @@ AArch64TTIImpl::getRegisterBitWidth(TargetTransformInfo::RegisterKind K) const {
   case TargetTransformInfo::RGK_Scalar:
     return TypeSize::getFixed(64);
   case TargetTransformInfo::RGK_FixedWidthVector:
-    if (!ST->isNeonAvailable() && !EnableFixedwidthAutovecInStreamingMode)
-      return TypeSize::getFixed(0);
-
-    if (ST->hasSVE())
+    if (ST->useSVEForFixedLengthVectors() &&
+        (ST->isSVEAvailable() || EnableFixedwidthAutovecInStreamingMode))
       return TypeSize::getFixed(
           std::max(ST->getMinSVEVectorSizeInBits(), 128u));
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paulwalker-arm wrote:

Alternatively you could implement `-mssve-vector-bits` to allow both quantities to be set independently and then only allow it to be use for streaming compatible functions when the both are specified and equal.  Perhaps I've talked myself into this needing a separate PR :)

https://github.com/llvm/llvm-project/pull/96305