[llvm] [AArch64] Don't allow mixed partial reductions without i8mm (PR #137602)

[Sander de Smalen via llvm-commits]

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@@ -5345,10 +5345,9 @@ InstructionCost AArch64TTIImpl::getPartialReductionCost(
     return Invalid;
 
   // AArch64 supports lowering mixed extensions to a usdot but only if the
-  // i8mm or sve/streaming features are available.
+  // i8mm feature is available.
   if (OpAExtend == TTI::PR_None || OpBExtend == TTI::PR_None ||
-      (OpAExtend != OpBExtend && !ST->hasMatMulInt8() &&
-       !ST->isSVEorStreamingSVEAvailable()))
+      (OpAExtend != OpBExtend && !ST->hasMatMulInt8()))
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sdesmalen-arm wrote:

It seems I forgot that there was also a corresponding NEON instruction. The code above already checks to see if SVE/Streaming-SVE is available when the type is scalable, or if NEON is available when the type is fixed-length, so only checking for i8mm here should indeed be sufficient. Could you add a test-case for the NEON case?

https://github.com/llvm/llvm-project/pull/137602