[llvm] [AArch64] Set the default streaming hazard size to 1024 for +sme,+sve (PR #123753)

[Sander de Smalen via llvm-commits]

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@@ -179,7 +179,12 @@ class AArch64Subtarget final : public AArch64GenSubtargetInfo {
 
   /// Returns the size of memory region that if accessed by both the CPU and
   /// the SME unit could result in a hazard. 0 = disabled.
-  unsigned getStreamingHazardSize() const { return StreamingHazardSize; }
+  unsigned getStreamingHazardSize() const {
+    // If StreamingHazardSize has been explicitly set to a value, use that.
+    // Otherwise, default to 1024 bytes when both SME and SVE are available,
+    // for all other configurations default to no streaming hazards.
+    return StreamingHazardSize.value_or(hasSME() && hasSVE() ? 1024 : 0);
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sdesmalen-arm wrote:

Please also add a check that `!hasSMEFA64()` (because if FA64 is available, then I wouldn't expect any hazards)

https://github.com/llvm/llvm-project/pull/123753