[llvm] [LV]Enable max safe distance in predicated DataWithEVL vectorization mode. (PR #100755)

[Florian Hahn via llvm-commits]

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@@ -3890,11 +3914,28 @@ 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);
-
-  auto MaxSafeFixedVF = ElementCount::getFixed(MaxSafeElements);
-  auto MaxSafeScalableVF = getMaxLegalScalableVF(MaxSafeElements);
+  unsigned MaxSafeElements = Legal->getMaxSafeVectorWidthInBits() / WidestType;
+  if (Legal->isSafeForAnyVectorWidth())
+    MaxSafeElements = bit_ceil(MaxSafeElements);
+  unsigned MaxSafeElementsPowerOf2 = bit_floor(std::gcd(
+      MaxSafeElements, Legal->getMaxStoreLoadForwardSafeVFPowerOf2().value_or(
+                           1ULL << countr_zero(MaxSafeElements))));
+
+  auto MaxSafeFixedVF = ElementCount::getFixed(MaxSafeElementsPowerOf2);
+  auto MaxSafeScalableVF = getMaxLegalScalableVF(MaxSafeElementsPowerOf2);
+  if (FoldTailByMasking && AllowNonPowerOf2SafeDist) {
+    if (std::optional<unsigned> SafeStoreLoadForwardingDist =
+            Legal->getMaxStoreLoadForwardSafeVFNonPowerOf2()) {
+      unsigned SafeDist = *SafeStoreLoadForwardingDist;
+      if (MaxSafeElements >= SafeDist)
+        MaxSafeElements = SafeDist;
+      else
+        MaxSafeElements = std::max(std::gcd(MaxSafeElements, SafeDist),
+                                   MaxSafeElementsPowerOf2);
+    }
+    MaxSafeScalableVF =
+        getMaxLegalScalableVF(std::numeric_limits<unsigned>::max());
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fhahn wrote:

Why ignore MaxSafeElements here?

This will somehow set the MaxSaclableVF to non-power-of-2?

https://github.com/llvm/llvm-project/pull/100755