[llvm] [LV]Split store-load forward distance analysis from other checks, NFC (PR #121156)

[Florian Hahn via llvm-commits]

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@@ -1756,31 +1757,38 @@ bool MemoryDepChecker::couldPreventStoreLoadForward(uint64_t Distance,
   // cause any slowdowns.
   const uint64_t NumItersForStoreLoadThroughMemory = 8 * TypeByteSize;
   // Maximum vector factor.
-  uint64_t MaxVFWithoutSLForwardIssues = std::min(
-      VectorizerParams::MaxVectorWidth * TypeByteSize, MinDepDistBytes);
+  uint64_t MaxVFWithoutSLForwardIssuesPowerOf2 =
+      std::min(VectorizerParams::MaxVectorWidth * TypeByteSize,
+               MaxStoreLoadForwardSafeDistanceInBits);
 
   // Compute the smallest VF at which the store and load would be misaligned.
-  for (uint64_t VF = 2 * TypeByteSize; VF <= MaxVFWithoutSLForwardIssues;
-       VF *= 2) {
+  for (uint64_t VF = 2 * TypeByteSize;
+       VF <= MaxVFWithoutSLForwardIssuesPowerOf2; VF *= 2) {
     // If the number of vector iteration between the store and the load are
     // small we could incur conflicts.
     if (Distance % VF && Distance / VF < NumItersForStoreLoadThroughMemory) {
-      MaxVFWithoutSLForwardIssues = (VF >> 1);
+      MaxVFWithoutSLForwardIssuesPowerOf2 = (VF >> 1);
       break;
     }
   }
 
-  if (MaxVFWithoutSLForwardIssues < 2 * TypeByteSize) {
+  if (MaxVFWithoutSLForwardIssuesPowerOf2 < 2 * TypeByteSize) {
     LLVM_DEBUG(
         dbgs() << "LAA: Distance " << Distance
                << " that could cause a store-load forwarding conflict\n");
     return true;
   }
 
-  if (MaxVFWithoutSLForwardIssues < MinDepDistBytes &&
-      MaxVFWithoutSLForwardIssues !=
-          VectorizerParams::MaxVectorWidth * TypeByteSize)
-    MinDepDistBytes = MaxVFWithoutSLForwardIssues;
+  if (CommonStride &&
+      MaxVFWithoutSLForwardIssuesPowerOf2 <
+          MaxStoreLoadForwardSafeDistanceInBits &&
+      MaxVFWithoutSLForwardIssuesPowerOf2 !=
+          VectorizerParams::MaxVectorWidth * TypeByteSize) {
+    uint64_t MaxVF = MaxVFWithoutSLForwardIssuesPowerOf2 / CommonStride;
----------------
fhahn wrote:

https://github.com/llvm/llvm-project/issues/134696 uncovered a case where MaxVF may not be a power of 2, as common-stride may not be a power of 2.

Fixed for now using bit_floor: 995fd47944f471e985e34d7da8c0667059decbac

https://github.com/llvm/llvm-project/pull/121156