[llvm] [LoopVectorize] Perform loop versioning for some early exit loops (PR #120603)

[Paul Walker via llvm-commits]

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@@ -1585,6 +1591,22 @@ class LoopVectorizationCostModel {
                                        ElementCount MaxSafeVF,
                                        bool FoldTailByMasking);
 
+  bool isSafeForAnyVectorWidth() const {
+    return Legal->isSafeForAnyVectorWidth() &&
+           (!Legal->hasUncountableEarlyExit() ||
+            !Legal->getNumPotentiallyFaultingLoads());
+  }
+
+  uint64_t getMaxSafeVectorWidthInBits() const {
+    uint64_t MaxSafeVectorWidth = Legal->getMaxSafeVectorWidthInBits();
+    // The legalizer bails out if getMinPageSize does not return a value.
+    if (Legal->hasUncountableEarlyExit() &&
+        Legal->getNumPotentiallyFaultingLoads())
+      MaxSafeVectorWidth =
+          std::min(MaxSafeVectorWidth, uint64_t(*TTI.getMinPageSize()) * 8);
+    return MaxSafeVectorWidth;
+  }
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paulwalker-arm wrote:

Similar to above in that `Legal->getMaxSafeVectorWidthInBits()` really should give the correct answer at all times because otherwise it's too easy to tie yourself in knots not knowing which version is valid at which time.

https://github.com/llvm/llvm-project/pull/120603