[llvm] [LV]Fix max safe elements calculations (PR #122148)

[Alexey Bataev via llvm-commits]

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@@ -3943,11 +3943,13 @@ FixedScalableVFPair LoopVectorizationCostModel::computeFeasibleMaxVF(
   // It is computed by MaxVF * sizeOf(type) * 8, where type is taken from
   // the memory accesses that is most restrictive (involved in the smallest
   // dependence distance).
-  unsigned MaxSafeElements =
-      llvm::bit_floor(Legal->getMaxSafeVectorWidthInBits() / WidestType);
+  unsigned MaxSafeElements = Legal->getMaxSafeVectorWidthInBits() / WidestType;
+  if (Legal->isSafeForAnyVectorWidth())
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alexey-bataev wrote:

No, actually WidestType is always of power of 2. Legal->getMaxSafeVectorWidthInBits() can be non-power-of-2 because of load-store forwarding, if there is non-power-of-2 dependency between loads/stores.
Another problem is that if Legal->isSafeForAnyVectorWidth(), then Legal->getMaxSafeVectorWidthInBits() return UMAX_INT, which is non-power-of (2^64-1), so need to use bit_ceil to avoid some (potential) VF dropping.

https://github.com/llvm/llvm-project/pull/122148