!fixup addres comments, thanks!

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -2444,19 +2444,20 @@ void InnerLoopVectorizer::emitIterationCountCheck(BasicBlock *Bypass) {
     ScalarEvolution &SE = *PSE.getSE();
     // TODO: Emit unconditional branch to vector preheader instead of
     // conditional branch with known condition.
-    const SCEV *TripCountSCEV = SE.getSCEV(Count);
+    const SCEV *TripCountSCEV = SE.applyLoopGuards(SE.getSCEV(Count), OrigLoop);
     // Check if the trip count is < the step.
-    if (SE.isKnownPredicate(P, SE.applyLoopGuards(TripCountSCEV, OrigLoop),
-                            SE.getSCEV(Step))) {
-      // TODO: Should not attempt to vectorize when the vector loop is known to
-      // never execute.
+    if (SE.isKnownPredicate(P, TripCountSCEV, SE.getSCEV(Step))) {
+      // TODO: Ensure step is at most the trip count when determining max VF and
+      // UF, w/o tail folding.
       CheckMinIters = Builder.getTrue();
     } else if (!SE.isKnownPredicate(CmpInst::getInversePredicate(P),
-                                    SE.applyLoopGuards(TripCountSCEV, OrigLoop),
-                                    SE.getSCEV(Step))) {
-      // Only generate the minimum iteration check only if we cannot prove the
-      // check is known to be false.
+                                    TripCountSCEV, SE.getSCEV(Step))) {
+      // Generate the minimum iteration check only if we cannot prove the
+      // check is known to be true, or known to be false
       CheckMinIters = Builder.CreateICmp(P, Count, Step, "min.iters.check");
+
+      // else step is known to be smaller than trip count, use CheckMinIters
+      // preset to false.
     }
   } else if (VF.isScalable() &&
              !isIndvarOverflowCheckKnownFalse(Cost, VF, UF) &&
@@ -2473,12 +2474,11 @@ void InnerLoopVectorizer::emitIterationCountCheck(BasicBlock *Bypass) {
     Value *Step = CreateStep();
     ScalarEvolution &SE = *PSE.getSE();
     // Check if we can prove that the trip count is >= the step.
-    // TODO: Emit unconditional branch to vector preheader instead of
-    // conditional branch with known condition.
-    const SCEV *TripCountSCEV = SE.getSCEV(LHS);
-    assert(!SE.isKnownPredicate(CmpInst::getInversePredicate(ICmpInst::ICMP_ULT),
-                            SE.applyLoopGuards(TripCountSCEV, OrigLoop),
-                            SE.getSCEV(Step)) && "SCEV unexpectedly proved overflow check to be known);
+    const SCEV *TripCountSCEV = SE.applyLoopGuards(SE.getSCEV(LHS), OrigLoop);
+    assert(
+        !SE.isKnownPredicate(CmpInst::getInversePredicate(ICmpInst::ICMP_ULT),
+                             TripCountSCEV, SE.getSCEV(Step)) &&
+        "SCEV unexpectedly proved overflow check to be known");
     // Don't execute the vector loop if (UMax - n) < (VF * UF).
     CheckMinIters = Builder.CreateICmp(ICmpInst::ICMP_ULT, LHS, Step);
   }

llvm/test/Transforms/LoopVectorize/version-stride-with-integer-casts.ll

@@ -488,8 +488,7 @@ define void @sext_of_i1_stride(i1 %g, ptr %dst) mustprogress {
 ; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[UMAX]], -1
 ; CHECK-NEXT:    [[TMP1:%.*]] = udiv i64 [[TMP0]], [[G_64]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = add nuw nsw i64 [[TMP1]], 1
-; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[TMP2]], 4
-; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_SCEVCHECK:%.*]]
+; CHECK-NEXT:    br i1 true, label [[SCALAR_PH:%.*]], label [[VECTOR_SCEVCHECK:%.*]]
 ; CHECK:       vector.scevcheck:
 ; CHECK-NEXT:    [[IDENT_CHECK:%.*]] = icmp ne i1 [[G]], true
 ; CHECK-NEXT:    br i1 [[IDENT_CHECK]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]