[llvm] [LV] Don't vectorize if trip count expansion may introduce UB. (PR #92177)

Florian Hahn via llvm-commits llvm-commits at lists.llvm.org
Wed May 15 04:47:07 PDT 2024


https://github.com/fhahn updated https://github.com/llvm/llvm-project/pull/92177

>From 49c699d0a832a12e9d93fbb581ac5dbda5eb6882 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Tue, 14 May 2024 20:36:16 +0100
Subject: [PATCH 1/2] [LV] Don't vectorize if trip count expansion may
 introduce UB.

Introduce a utility to check if a SCEV expansion may introduce UB
(couldn't find a similar utility after a quick glance) and use to the
avoid vectorizing when expanding the trip count introduces UB.

Fixes https://github.com/llvm/llvm-project/issues/89958.
---
 .../Utils/ScalarEvolutionExpander.h           |   4 +
 .../Utils/ScalarEvolutionExpander.cpp         |   5 +
 .../Vectorize/LoopVectorizationLegality.cpp   |  26 +++++
 .../trip-count-expansion-may-introduce-ub.ll  | 100 ++----------------
 4 files changed, 41 insertions(+), 94 deletions(-)

diff --git a/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h b/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
index 62c1e15a9a60e..270286afebd2a 100644
--- a/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
+++ b/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
@@ -418,6 +418,10 @@ class SCEVExpander : public SCEVVisitor<SCEVExpander, Value *> {
   BasicBlock::iterator findInsertPointAfter(Instruction *I,
                                             Instruction *MustDominate) const;
 
+  /// Returns true if expanding \p Expr may introduce UB (e.g. because the
+  /// expression contains an UDiv expression).
+  static bool expansionMayIntroduceUB(const SCEV *Expr);
+
 private:
   LLVMContext &getContext() const { return SE.getContext(); }
 
diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index 0feea0a4233cd..0a5ec8baccbee 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -161,6 +161,11 @@ SCEVExpander::findInsertPointAfter(Instruction *I,
   return IP;
 }
 
+bool SCEVExpander::expansionMayIntroduceUB(const SCEV *Expr) {
+  return SCEVExprContains(Expr,
+                          [](const SCEV *Op) { return isa<SCEVUDivExpr>(Op); });
+}
+
 BasicBlock::iterator
 SCEVExpander::GetOptimalInsertionPointForCastOf(Value *V) const {
   // Cast the argument at the beginning of the entry block, after
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 9de49d1bcfeac..e1b1ad083f184 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -24,6 +24,7 @@
 #include "llvm/Analysis/VectorUtils.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/PatternMatch.h"
+#include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
 #include "llvm/Transforms/Utils/SizeOpts.h"
 #include "llvm/Transforms/Vectorize/LoopVectorize.h"
 
@@ -1506,6 +1507,31 @@ bool LoopVectorizationLegality::canVectorize(bool UseVPlanNativePath) {
       return false;
   }
 
+  SmallVector<BasicBlock *> Exiting;
+  TheLoop->getExitingBlocks(Exiting);
+  // Check if eexit count for any exit that may execute unconditionally may in
+  // introduce UB. Note that we can skip checks in the header or if there's a
+  // single exit, as in those cases we know that the exit count will be
+  // evaluated in each loop iteration. There are other cases where the exiting
+  // block executes on each loop iteration, but we don't have a cheap way to
+  // check at the moment.
+  ScalarEvolution &SE = *PSE.getSE();
+  if (Exiting.size() > 1 && any_of(Exiting, [this, &SE](BasicBlock *E) {
+        if (TheLoop->getHeader() == E)
+          return false;
+        const SCEV *EC = SE.getExitCount(TheLoop, E);
+        return !isa<SCEVCouldNotCompute>(EC) &&
+               SCEVExpander::expansionMayIntroduceUB(EC);
+      })) {
+    LLVM_DEBUG(
+        dbgs()
+        << "LV: Expanding the trip count expression may introduce UB.\n");
+    if (DoExtraAnalysis)
+      Result = false;
+    else
+      return false;
+  }
+
   LLVM_DEBUG(dbgs() << "LV: We can vectorize this loop"
                     << (LAI->getRuntimePointerChecking()->Need
                             ? " (with a runtime bound check)"
diff --git a/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll b/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll
index 85fad6fb36328..168c0f88e4fc0 100644
--- a/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll
+++ b/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll
@@ -74,66 +74,9 @@ define i64 @multi_exit_2_exit_count_with_udiv_in_block_executed_unconditionally(
 ; CHECK-LABEL: define i64 @multi_exit_2_exit_count_with_udiv_in_block_executed_unconditionally(
 ; CHECK-SAME: ptr [[A:%.*]], i64 [[N:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SMAX:%.*]] = call i64 @llvm.smax.i64(i64 [[N]], i64 0)
-; CHECK-NEXT:    [[TMP0:%.*]] = udiv i64 42, [[N]]
-; CHECK-NEXT:    [[UMIN:%.*]] = call i64 @llvm.umin.i64(i64 [[SMAX]], i64 [[TMP0]])
-; CHECK-NEXT:    [[TMP1:%.*]] = add nuw nsw i64 [[UMIN]], 1
-; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ule i64 [[TMP1]], 4
-; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
-; CHECK:       vector.ph:
-; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[TMP1]], 4
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[N_MOD_VF]], 0
-; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[TMP2]], i64 4, i64 [[N_MOD_VF]]
-; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[TMP1]], [[TMP3]]
-; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
-; CHECK:       vector.body:
-; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[PRED_STORE_CONTINUE6:%.*]] ]
-; CHECK-NEXT:    [[TMP4:%.*]] = add i64 [[INDEX]], 0
-; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[TMP4]]
-; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i32, ptr [[TMP5]], i32 0
-; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i32>, ptr [[TMP6]], align 4
-; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq <4 x i32> [[WIDE_LOAD]], <i32 10, i32 10, i32 10, i32 10>
-; CHECK-NEXT:    [[TMP8:%.*]] = extractelement <4 x i1> [[TMP7]], i32 0
-; CHECK-NEXT:    br i1 [[TMP8]], label [[PRED_STORE_IF:%.*]], label [[PRED_STORE_CONTINUE:%.*]]
-; CHECK:       pred.store.if:
-; CHECK-NEXT:    [[TMP9:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[TMP4]]
-; CHECK-NEXT:    store i32 1, ptr [[TMP9]], align 4
-; CHECK-NEXT:    br label [[PRED_STORE_CONTINUE]]
-; CHECK:       pred.store.continue:
-; CHECK-NEXT:    [[TMP10:%.*]] = extractelement <4 x i1> [[TMP7]], i32 1
-; CHECK-NEXT:    br i1 [[TMP10]], label [[PRED_STORE_IF1:%.*]], label [[PRED_STORE_CONTINUE2:%.*]]
-; CHECK:       pred.store.if1:
-; CHECK-NEXT:    [[TMP11:%.*]] = add i64 [[INDEX]], 1
-; CHECK-NEXT:    [[TMP12:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[TMP11]]
-; CHECK-NEXT:    store i32 1, ptr [[TMP12]], align 4
-; CHECK-NEXT:    br label [[PRED_STORE_CONTINUE2]]
-; CHECK:       pred.store.continue2:
-; CHECK-NEXT:    [[TMP13:%.*]] = extractelement <4 x i1> [[TMP7]], i32 2
-; CHECK-NEXT:    br i1 [[TMP13]], label [[PRED_STORE_IF3:%.*]], label [[PRED_STORE_CONTINUE4:%.*]]
-; CHECK:       pred.store.if3:
-; CHECK-NEXT:    [[TMP14:%.*]] = add i64 [[INDEX]], 2
-; CHECK-NEXT:    [[TMP15:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[TMP14]]
-; CHECK-NEXT:    store i32 1, ptr [[TMP15]], align 4
-; CHECK-NEXT:    br label [[PRED_STORE_CONTINUE4]]
-; CHECK:       pred.store.continue4:
-; CHECK-NEXT:    [[TMP16:%.*]] = extractelement <4 x i1> [[TMP7]], i32 3
-; CHECK-NEXT:    br i1 [[TMP16]], label [[PRED_STORE_IF5:%.*]], label [[PRED_STORE_CONTINUE6]]
-; CHECK:       pred.store.if5:
-; CHECK-NEXT:    [[TMP17:%.*]] = add i64 [[INDEX]], 3
-; CHECK-NEXT:    [[TMP18:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[TMP17]]
-; CHECK-NEXT:    store i32 1, ptr [[TMP18]], align 4
-; CHECK-NEXT:    br label [[PRED_STORE_CONTINUE6]]
-; CHECK:       pred.store.continue6:
-; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
-; CHECK-NEXT:    [[TMP19:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[TMP19]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
-; CHECK:       middle.block:
-; CHECK-NEXT:    br label [[SCALAR_PH]]
-; CHECK:       scalar.ph:
-; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
 ; CHECK:       loop.header:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
 ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[IV]]
 ; CHECK-NEXT:    [[L:%.*]] = load i32, ptr [[GEP]], align 4
 ; CHECK-NEXT:    [[C_2:%.*]] = icmp eq i32 [[L]], 10
@@ -148,7 +91,7 @@ define i64 @multi_exit_2_exit_count_with_udiv_in_block_executed_unconditionally(
 ; CHECK:       loop.latch:
 ; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
 ; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV]], [[N]]
-; CHECK-NEXT:    br i1 [[C_0]], label [[LOOP_HEADER]], label [[EXIT]], !llvm.loop [[LOOP5:![0-9]+]]
+; CHECK-NEXT:    br i1 [[C_0]], label [[LOOP_HEADER]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[CONTINUE]] ], [ 0, [[LOOP_LATCH]] ]
 ; CHECK-NEXT:    ret i64 [[P]]
@@ -232,40 +175,13 @@ exit:
   ret i64 %p
 }
 
-; FIXME: Currently miscompiled as we unconditionally execute udiv after
-; vectorization.
 define i64 @multi_exit_4_exit_count_with_udiv_in_latch(ptr %dst, i64 %N) {
 ; CHECK-LABEL: define i64 @multi_exit_4_exit_count_with_udiv_in_latch(
 ; CHECK-SAME: ptr [[DST:%.*]], i64 [[N:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SMAX:%.*]] = call i64 @llvm.smax.i64(i64 [[N]], i64 0)
-; CHECK-NEXT:    [[TMP0:%.*]] = udiv i64 42, [[N]]
-; CHECK-NEXT:    [[UMIN:%.*]] = call i64 @llvm.umin.i64(i64 [[SMAX]], i64 [[TMP0]])
-; CHECK-NEXT:    [[TMP1:%.*]] = add nuw nsw i64 [[UMIN]], 1
-; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ule i64 [[TMP1]], 4
-; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
-; CHECK:       vector.ph:
-; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[TMP1]], 4
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[N_MOD_VF]], 0
-; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[TMP2]], i64 4, i64 [[N_MOD_VF]]
-; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[TMP1]], [[TMP3]]
-; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
-; CHECK:       vector.body:
-; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[TMP4:%.*]] = add i64 [[INDEX]], 0
-; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[TMP4]]
-; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i32, ptr [[TMP5]], i32 0
-; CHECK-NEXT:    store <4 x i32> <i32 1, i32 1, i32 1, i32 1>, ptr [[TMP6]], align 4
-; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
-; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[TMP7]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
-; CHECK:       middle.block:
-; CHECK-NEXT:    br label [[SCALAR_PH]]
-; CHECK:       scalar.ph:
-; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
 ; CHECK:       loop.header:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
 ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[IV]]
 ; CHECK-NEXT:    store i32 1, ptr [[GEP]], align 4
 ; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV]], [[N]]
@@ -274,7 +190,7 @@ define i64 @multi_exit_4_exit_count_with_udiv_in_latch(ptr %dst, i64 %N) {
 ; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
 ; CHECK-NEXT:    [[D:%.*]] = udiv i64 42, [[N]]
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV]], [[D]]
-; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_HEADER]], label [[EXIT]], !llvm.loop [[LOOP7:![0-9]+]]
+; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_HEADER]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[LOOP_HEADER]] ], [ 0, [[LOOP_LATCH]] ]
 ; CHECK-NEXT:    ret i64 [[P]]
@@ -320,7 +236,7 @@ define void @single_exit_tc_with_udiv(ptr %dst, i64 %N) {
 ; CHECK-NEXT:    store <4 x i32> <i32 1, i32 1, i32 1, i32 1>, ptr [[TMP4]], align 4
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
 ; CHECK-NEXT:    [[TMP5:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[TMP5]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
+; CHECK-NEXT:    br i1 [[TMP5]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 [[TMP1]], [[N_VEC]]
 ; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
@@ -334,7 +250,7 @@ define void @single_exit_tc_with_udiv(ptr %dst, i64 %N) {
 ; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
 ; CHECK-NEXT:    [[D:%.*]] = udiv i64 42, [[N]]
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV]], [[D]]
-; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP]], label [[EXIT]], !llvm.loop [[LOOP9:![0-9]+]]
+; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP]], label [[EXIT]], !llvm.loop [[LOOP5:![0-9]+]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -361,8 +277,4 @@ exit:
 ; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META2]], [[META1]]}
 ; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META1]], [[META2]]}
 ; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META2]], [[META1]]}
-; CHECK: [[LOOP6]] = distinct !{[[LOOP6]], [[META1]], [[META2]]}
-; CHECK: [[LOOP7]] = distinct !{[[LOOP7]], [[META2]], [[META1]]}
-; CHECK: [[LOOP8]] = distinct !{[[LOOP8]], [[META1]], [[META2]]}
-; CHECK: [[LOOP9]] = distinct !{[[LOOP9]], [[META2]], [[META1]]}
 ;.

>From e25bdcc5e739f29aa825fee102578afc76f2a105 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Wed, 15 May 2024 12:46:10 +0100
Subject: [PATCH 2/2] !fixup also check divisor != 0.

---
 .../Utils/ScalarEvolutionExpander.h           |   4 +-
 .../Utils/ScalarEvolutionExpander.cpp         |   9 +-
 .../Vectorize/LoopVectorizationLegality.cpp   |   2 +-
 .../trip-count-expansion-may-introduce-ub.ll  | 194 +++++++-----------
 4 files changed, 84 insertions(+), 125 deletions(-)

diff --git a/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h b/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
index 270286afebd2a..911143ca4280c 100644
--- a/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
+++ b/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
@@ -419,8 +419,8 @@ class SCEVExpander : public SCEVVisitor<SCEVExpander, Value *> {
                                             Instruction *MustDominate) const;
 
   /// Returns true if expanding \p Expr may introduce UB (e.g. because the
-  /// expression contains an UDiv expression).
-  static bool expansionMayIntroduceUB(const SCEV *Expr);
+  /// expression contains an UDiv expression with a divisor that may be 0).
+  static bool expansionMayIntroduceUB(const SCEV *Expr, ScalarEvolution &SE);
 
 private:
   LLVMContext &getContext() const { return SE.getContext(); }
diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index 0a5ec8baccbee..36e4797409569 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -161,9 +161,12 @@ SCEVExpander::findInsertPointAfter(Instruction *I,
   return IP;
 }
 
-bool SCEVExpander::expansionMayIntroduceUB(const SCEV *Expr) {
-  return SCEVExprContains(Expr,
-                          [](const SCEV *Op) { return isa<SCEVUDivExpr>(Op); });
+bool SCEVExpander::expansionMayIntroduceUB(const SCEV *Expr,
+                                           ScalarEvolution &SE) {
+  return SCEVExprContains(Expr, [&SE](const SCEV *Op) {
+    const auto *UDiv = dyn_cast<SCEVUDivExpr>(Op);
+    return UDiv && !SE.isKnownNonZero(UDiv->getOperand(1));
+  });
 }
 
 BasicBlock::iterator
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index e1b1ad083f184..b86932cb03667 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -1521,7 +1521,7 @@ bool LoopVectorizationLegality::canVectorize(bool UseVPlanNativePath) {
           return false;
         const SCEV *EC = SE.getExitCount(TheLoop, E);
         return !isa<SCEVCouldNotCompute>(EC) &&
-               SCEVExpander::expansionMayIntroduceUB(EC);
+               SCEVExpander::expansionMayIntroduceUB(EC, SE);
       })) {
     LLVM_DEBUG(
         dbgs()
diff --git a/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll b/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll
index b1605e156cc66..742078ad75137 100644
--- a/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll
+++ b/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll
@@ -140,10 +140,10 @@ define i64 @multi_exit_2_exit_count_with_udiv_by_value_in_block_executed_uncondi
 ; CHECK-LABEL: define i64 @multi_exit_2_exit_count_with_udiv_by_value_in_block_executed_unconditionally(
 ; CHECK-SAME: ptr [[A:%.*]], i64 [[N:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
+; CHECK-NEXT:    br label [[LOOP_HEADER1:%.*]]
 ; CHECK:       loop.header:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[IV]]
+; CHECK-NEXT:    [[IV1:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT1:%.*]], [[LOOP_LATCH1:%.*]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[IV1]]
 ; CHECK-NEXT:    [[L:%.*]] = load i32, ptr [[GEP]], align 4
 ; CHECK-NEXT:    [[C_2:%.*]] = icmp eq i32 [[L]], 10
 ; CHECK-NEXT:    br i1 [[C_2]], label [[THEN:%.*]], label [[CONTINUE:%.*]]
@@ -152,13 +152,14 @@ define i64 @multi_exit_2_exit_count_with_udiv_by_value_in_block_executed_uncondi
 ; CHECK-NEXT:    br label [[CONTINUE]]
 ; CHECK:       continue:
 ; CHECK-NEXT:    [[D:%.*]] = udiv i64 42, [[N]]
-; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV]], [[D]]
-; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV1]], [[D]]
+; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_LATCH1]], label [[EXIT:%.*]]
 ; CHECK:       loop.latch:
-; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
-; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV]], [[N]]
+; CHECK-NEXT:    [[IV_NEXT1]] = add i64 [[IV1]], 1
+; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV1]], [[N]]
+; CHECK-NEXT:    br i1 [[C_0]], label [[LOOP_HEADER1]], label [[EXIT]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[CONTINUE]] ], [ 0, [[LOOP_LATCH]] ]
+; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[CONTINUE]] ], [ 0, [[LOOP_LATCH1]] ]
 ; CHECK-NEXT:    ret i64 [[P]]
 ;
 entry:
@@ -199,16 +200,16 @@ define i64 @multi_exit_2_exit_count_with_udiv_by_constant_in_block_executed_unco
 ; CHECK-NEXT:    [[UMIN:%.*]] = call i64 @llvm.umin.i64(i64 [[SMAX]], i64 [[TMP0]])
 ; CHECK-NEXT:    [[TMP1:%.*]] = add nuw nsw i64 [[UMIN]], 1
 ; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ule i64 [[TMP1]], 4
-; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[ENTRY:%.*]]
 ; CHECK:       vector.ph:
 ; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[TMP1]], 4
 ; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[N_MOD_VF]], 0
 ; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[TMP2]], i64 4, i64 [[N_MOD_VF]]
 ; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[TMP1]], [[TMP3]]
-; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
 ; CHECK:       vector.body:
-; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[PRED_STORE_CONTINUE6:%.*]] ]
-; CHECK-NEXT:    [[TMP4:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
+; CHECK-NEXT:    [[TMP4:%.*]] = add i64 [[IV]], 0
 ; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[TMP4]]
 ; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i32, ptr [[TMP5]], i32 0
 ; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i32>, ptr [[TMP6]], align 4
@@ -223,7 +224,7 @@ define i64 @multi_exit_2_exit_count_with_udiv_by_constant_in_block_executed_unco
 ; CHECK-NEXT:    [[TMP10:%.*]] = extractelement <4 x i1> [[TMP7]], i32 1
 ; CHECK-NEXT:    br i1 [[TMP10]], label [[PRED_STORE_IF1:%.*]], label [[PRED_STORE_CONTINUE2:%.*]]
 ; CHECK:       pred.store.if1:
-; CHECK-NEXT:    [[TMP11:%.*]] = add i64 [[INDEX]], 1
+; CHECK-NEXT:    [[TMP11:%.*]] = add i64 [[IV]], 1
 ; CHECK-NEXT:    [[TMP12:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[TMP11]]
 ; CHECK-NEXT:    store i32 1, ptr [[TMP12]], align 4
 ; CHECK-NEXT:    br label [[PRED_STORE_CONTINUE2]]
@@ -231,30 +232,30 @@ define i64 @multi_exit_2_exit_count_with_udiv_by_constant_in_block_executed_unco
 ; CHECK-NEXT:    [[TMP13:%.*]] = extractelement <4 x i1> [[TMP7]], i32 2
 ; CHECK-NEXT:    br i1 [[TMP13]], label [[PRED_STORE_IF3:%.*]], label [[PRED_STORE_CONTINUE4:%.*]]
 ; CHECK:       pred.store.if3:
-; CHECK-NEXT:    [[TMP14:%.*]] = add i64 [[INDEX]], 2
+; CHECK-NEXT:    [[TMP14:%.*]] = add i64 [[IV]], 2
 ; CHECK-NEXT:    [[TMP15:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[TMP14]]
 ; CHECK-NEXT:    store i32 1, ptr [[TMP15]], align 4
 ; CHECK-NEXT:    br label [[PRED_STORE_CONTINUE4]]
 ; CHECK:       pred.store.continue4:
 ; CHECK-NEXT:    [[TMP16:%.*]] = extractelement <4 x i1> [[TMP7]], i32 3
-; CHECK-NEXT:    br i1 [[TMP16]], label [[PRED_STORE_IF5:%.*]], label [[PRED_STORE_CONTINUE6]]
+; CHECK-NEXT:    br i1 [[TMP16]], label [[PRED_STORE_IF5:%.*]], label [[LOOP_LATCH]]
 ; CHECK:       pred.store.if5:
-; CHECK-NEXT:    [[TMP17:%.*]] = add i64 [[INDEX]], 3
+; CHECK-NEXT:    [[TMP17:%.*]] = add i64 [[IV]], 3
 ; CHECK-NEXT:    [[TMP18:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[TMP17]]
 ; CHECK-NEXT:    store i32 1, ptr [[TMP18]], align 4
-; CHECK-NEXT:    br label [[PRED_STORE_CONTINUE6]]
+; CHECK-NEXT:    br label [[LOOP_LATCH]]
 ; CHECK:       pred.store.continue6:
-; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
-; CHECK-NEXT:    [[TMP19:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[TMP19]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
+; CHECK-NEXT:    [[IV_NEXT]] = add nuw i64 [[IV]], 4
+; CHECK-NEXT:    [[TMP19:%.*]] = icmp eq i64 [[IV_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP19]], label [[MIDDLE_BLOCK:%.*]], label [[LOOP_HEADER]], !llvm.loop [[LOOP6:![0-9]+]]
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    br label [[SCALAR_PH]]
 ; CHECK:       scalar.ph:
-; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
-; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY1:%.*]] ]
+; CHECK-NEXT:    br label [[LOOP_HEADER1:%.*]]
 ; CHECK:       loop.header:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[IV]]
+; CHECK-NEXT:    [[IV1:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT1:%.*]], [[LOOP_LATCH1:%.*]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[IV1]]
 ; CHECK-NEXT:    [[L:%.*]] = load i32, ptr [[GEP]], align 4
 ; CHECK-NEXT:    [[C_2:%.*]] = icmp eq i32 [[L]], 10
 ; CHECK-NEXT:    br i1 [[C_2]], label [[THEN:%.*]], label [[CONTINUE:%.*]]
@@ -263,14 +264,14 @@ define i64 @multi_exit_2_exit_count_with_udiv_by_constant_in_block_executed_unco
 ; CHECK-NEXT:    br label [[CONTINUE]]
 ; CHECK:       continue:
 ; CHECK-NEXT:    [[D:%.*]] = udiv i64 [[N]], 42
-; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV]], [[D]]
-; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV1]], [[D]]
+; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_LATCH1]], label [[EXIT:%.*]]
 ; CHECK:       loop.latch:
-; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
-; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV]], [[N]]
-; CHECK-NEXT:    br i1 [[C_0]], label [[LOOP_HEADER]], label [[EXIT]], !llvm.loop [[LOOP9:![0-9]+]]
+; CHECK-NEXT:    [[IV_NEXT1]] = add i64 [[IV1]], 1
+; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV1]], [[N]]
+; CHECK-NEXT:    br i1 [[C_0]], label [[LOOP_HEADER1]], label [[EXIT]], !llvm.loop [[LOOP7:![0-9]+]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[CONTINUE]] ], [ 0, [[LOOP_LATCH]] ]
+; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[CONTINUE]] ], [ 0, [[LOOP_LATCH1]] ]
 ; CHECK-NEXT:    ret i64 [[P]]
 ;
 entry:
@@ -401,37 +402,10 @@ exit:
   ret i64 %p
 }
 
-; FIXME: Currently miscompiled as we unconditionally execute udiv after
-; vectorization.
 define i64 @multi_exit_4_exit_count_with_udiv_by_value_in_latch(ptr %dst, i64 %N) {
 ; CHECK-LABEL: define i64 @multi_exit_4_exit_count_with_udiv_by_value_in_latch(
 ; CHECK-SAME: ptr [[DST:%.*]], i64 [[N:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SMAX:%.*]] = call i64 @llvm.smax.i64(i64 [[N]], i64 0)
-; CHECK-NEXT:    [[TMP0:%.*]] = udiv i64 42, [[N]]
-; CHECK-NEXT:    [[UMIN:%.*]] = call i64 @llvm.umin.i64(i64 [[SMAX]], i64 [[TMP0]])
-; CHECK-NEXT:    [[TMP1:%.*]] = add nuw nsw i64 [[UMIN]], 1
-; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ule i64 [[TMP1]], 4
-; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
-; CHECK:       vector.ph:
-; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[TMP1]], 4
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[N_MOD_VF]], 0
-; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[TMP2]], i64 4, i64 [[N_MOD_VF]]
-; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[TMP1]], [[TMP3]]
-; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
-; CHECK:       vector.body:
-; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[TMP4:%.*]] = add i64 [[INDEX]], 0
-; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[TMP4]]
-; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i32, ptr [[TMP5]], i32 0
-; CHECK-NEXT:    store <4 x i32> <i32 1, i32 1, i32 1, i32 1>, ptr [[TMP6]], align 4
-; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
-; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[TMP7]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP10:![0-9]+]]
-; CHECK:       middle.block:
-; CHECK-NEXT:    br label [[SCALAR_PH]]
-; CHECK:       scalar.ph:
-; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
 ; CHECK:       loop.header:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
@@ -443,6 +417,7 @@ define i64 @multi_exit_4_exit_count_with_udiv_by_value_in_latch(ptr %dst, i64 %N
 ; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
 ; CHECK-NEXT:    [[D:%.*]] = udiv i64 42, [[N]]
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV]], [[D]]
+; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_HEADER]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[LOOP_HEADER]] ], [ 0, [[LOOP_LATCH]] ]
 ; CHECK-NEXT:    ret i64 [[P]]
@@ -483,34 +458,34 @@ define i64 @multi_exit_4_exit_count_with_udiv_by_constant_in_latch(ptr %dst, i64
 ; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[N_MOD_VF]], 0
 ; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[TMP2]], i64 4, i64 [[N_MOD_VF]]
 ; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[TMP1]], [[TMP3]]
-; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
 ; CHECK:       vector.body:
-; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[TMP4:%.*]] = add i64 [[INDEX]], 0
-; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[TMP4]]
-; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i32, ptr [[TMP5]], i32 0
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[LOOP_HEADER]] ]
+; CHECK-NEXT:    [[IV:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[IV]]
+; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i32, ptr [[GEP]], i32 0
 ; CHECK-NEXT:    store <4 x i32> <i32 1, i32 1, i32 1, i32 1>, ptr [[TMP6]], align 4
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
 ; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[TMP7]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP12:![0-9]+]]
+; CHECK-NEXT:    br i1 [[TMP7]], label [[MIDDLE_BLOCK:%.*]], label [[LOOP_HEADER]], !llvm.loop [[LOOP8:![0-9]+]]
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    br label [[SCALAR_PH]]
 ; CHECK:       scalar.ph:
 ; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
-; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
+; CHECK-NEXT:    br label [[LOOP_HEADER1:%.*]]
 ; CHECK:       loop.header:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[IV]]
-; CHECK-NEXT:    store i32 1, ptr [[GEP]], align 4
-; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV]], [[N]]
+; CHECK-NEXT:    [[IV1:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[IV1]]
+; CHECK-NEXT:    store i32 1, ptr [[GEP1]], align 4
+; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV1]], [[N]]
 ; CHECK-NEXT:    br i1 [[C_0]], label [[LOOP_LATCH]], label [[EXIT:%.*]]
 ; CHECK:       loop.latch:
-; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV1]], 1
 ; CHECK-NEXT:    [[D:%.*]] = udiv i64 [[N]], 42
-; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV]], [[D]]
-; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_HEADER]], label [[EXIT]], !llvm.loop [[LOOP13:![0-9]+]]
+; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV1]], [[D]]
+; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_HEADER1]], label [[EXIT]], !llvm.loop [[LOOP9:![0-9]+]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[LOOP_HEADER]] ], [ 0, [[LOOP_LATCH]] ]
+; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[LOOP_HEADER1]] ], [ 0, [[LOOP_LATCH]] ]
 ; CHECK-NEXT:    ret i64 [[P]]
 ;
 entry:
@@ -554,6 +529,7 @@ define void @single_exit_tc_with_udiv(ptr %dst, i64 %N) {
 ; CHECK-NEXT:    store <4 x i32> <i32 1, i32 1, i32 1, i32 1>, ptr [[TMP4]], align 4
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
 ; CHECK-NEXT:    [[TMP5:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP5]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP10:![0-9]+]]
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 [[TMP1]], [[N_VEC]]
 ; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
@@ -567,6 +543,7 @@ define void @single_exit_tc_with_udiv(ptr %dst, i64 %N) {
 ; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
 ; CHECK-NEXT:    [[D:%.*]] = udiv i64 42, [[N]]
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV]], [[D]]
+; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP]], label [[EXIT]], !llvm.loop [[LOOP11:![0-9]+]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -586,43 +563,13 @@ exit:
   ret void
 }
 
-; FIXME: Currently miscompiled as we unconditionally execute udiv after
-; vectorization.
 define i64 @multi_exit_4_exit_count_with_urem_by_value_in_latch(ptr %dst, i64 %N) {
 ; CHECK-LABEL: define i64 @multi_exit_4_exit_count_with_urem_by_value_in_latch(
 ; CHECK-SAME: ptr [[DST:%.*]], i64 [[N:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SMAX:%.*]] = call i64 @llvm.smax.i64(i64 [[N]], i64 0)
-; CHECK-NEXT:    [[TMP0:%.*]] = udiv i64 42, [[N]]
-; CHECK-NEXT:    [[TMP1:%.*]] = mul nuw i64 [[N]], [[TMP0]]
-; CHECK-NEXT:    [[TMP2:%.*]] = sub i64 42, [[TMP1]]
-; CHECK-NEXT:    [[SMAX1:%.*]] = call i64 @llvm.smax.i64(i64 [[TMP2]], i64 0)
-; CHECK-NEXT:    [[UMIN:%.*]] = call i64 @llvm.umin.i64(i64 [[SMAX]], i64 [[SMAX1]])
-; CHECK-NEXT:    [[TMP3:%.*]] = add nuw i64 [[UMIN]], 1
-; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ule i64 [[TMP3]], 4
-; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
-; CHECK:       vector.ph:
-; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[TMP3]], 4
-; CHECK-NEXT:    [[TMP4:%.*]] = icmp eq i64 [[N_MOD_VF]], 0
-; CHECK-NEXT:    [[TMP5:%.*]] = select i1 [[TMP4]], i64 4, i64 [[N_MOD_VF]]
-; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[TMP3]], [[TMP5]]
-; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
-; CHECK:       vector.body:
-; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[TMP6:%.*]] = add i64 [[INDEX]], 0
-; CHECK-NEXT:    [[TMP7:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[TMP6]]
-; CHECK-NEXT:    [[TMP8:%.*]] = getelementptr inbounds i32, ptr [[TMP7]], i32 0
-; CHECK-NEXT:    store <4 x i32> <i32 1, i32 1, i32 1, i32 1>, ptr [[TMP8]], align 4
-; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
-; CHECK-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP16:![0-9]+]]
-; CHECK:       middle.block:
-; CHECK-NEXT:    br label [[SCALAR_PH]]
-; CHECK:       scalar.ph:
-; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
 ; CHECK:       loop.header:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
 ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[IV]]
 ; CHECK-NEXT:    store i32 1, ptr [[GEP]], align 4
 ; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV]], [[N]]
@@ -631,7 +578,7 @@ define i64 @multi_exit_4_exit_count_with_urem_by_value_in_latch(ptr %dst, i64 %N
 ; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
 ; CHECK-NEXT:    [[D:%.*]] = urem i64 42, [[N]]
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV]], [[D]]
-; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_HEADER]], label [[EXIT]], !llvm.loop [[LOOP17:![0-9]+]]
+; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_HEADER]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[LOOP_HEADER]] ], [ 0, [[LOOP_LATCH]] ]
 ; CHECK-NEXT:    ret i64 [[P]]
@@ -675,34 +622,34 @@ define i64 @multi_exit_4_exit_count_with_urem_by_constant_in_latch(ptr %dst, i64
 ; CHECK-NEXT:    [[TMP4:%.*]] = icmp eq i64 [[N_MOD_VF]], 0
 ; CHECK-NEXT:    [[TMP5:%.*]] = select i1 [[TMP4]], i64 4, i64 [[N_MOD_VF]]
 ; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[TMP3]], [[TMP5]]
-; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
 ; CHECK:       vector.body:
-; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[TMP6:%.*]] = add i64 [[INDEX]], 0
-; CHECK-NEXT:    [[TMP7:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[TMP6]]
-; CHECK-NEXT:    [[TMP8:%.*]] = getelementptr inbounds i32, ptr [[TMP7]], i32 0
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[LOOP_HEADER]] ]
+; CHECK-NEXT:    [[IV:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[IV]]
+; CHECK-NEXT:    [[TMP8:%.*]] = getelementptr inbounds i32, ptr [[GEP]], i32 0
 ; CHECK-NEXT:    store <4 x i32> <i32 1, i32 1, i32 1, i32 1>, ptr [[TMP8]], align 4
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
 ; CHECK-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP18:![0-9]+]]
+; CHECK-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[LOOP_HEADER]], !llvm.loop [[LOOP12:![0-9]+]]
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    br label [[SCALAR_PH]]
 ; CHECK:       scalar.ph:
 ; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
-; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
+; CHECK-NEXT:    br label [[LOOP_HEADER1:%.*]]
 ; CHECK:       loop.header:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[IV]]
-; CHECK-NEXT:    store i32 1, ptr [[GEP]], align 4
-; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV]], [[N]]
+; CHECK-NEXT:    [[IV1:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr inbounds i32, ptr [[DST]], i64 [[IV1]]
+; CHECK-NEXT:    store i32 1, ptr [[GEP1]], align 4
+; CHECK-NEXT:    [[C_0:%.*]] = icmp slt i64 [[IV1]], [[N]]
 ; CHECK-NEXT:    br i1 [[C_0]], label [[LOOP_LATCH]], label [[EXIT:%.*]]
 ; CHECK:       loop.latch:
-; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV1]], 1
 ; CHECK-NEXT:    [[D:%.*]] = urem i64 [[N]], 42
-; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV]], [[D]]
-; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_HEADER]], label [[EXIT]], !llvm.loop [[LOOP19:![0-9]+]]
+; CHECK-NEXT:    [[C_1:%.*]] = icmp slt i64 [[IV1]], [[D]]
+; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_HEADER1]], label [[EXIT]], !llvm.loop [[LOOP13:![0-9]+]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[LOOP_HEADER]] ], [ 0, [[LOOP_LATCH]] ]
+; CHECK-NEXT:    [[P:%.*]] = phi i64 [ 1, [[LOOP_HEADER1]] ], [ 0, [[LOOP_LATCH]] ]
 ; CHECK-NEXT:    ret i64 [[P]]
 ;
 entry:
@@ -815,3 +762,12 @@ exit:
 ; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META2]], [[META1]]}
 ; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META1]], [[META2]]}
 ; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META2]], [[META1]]}
+; CHECK: [[LOOP6]] = distinct !{[[LOOP6]], [[META1]], [[META2]]}
+; CHECK: [[LOOP7]] = distinct !{[[LOOP7]], [[META2]], [[META1]]}
+; CHECK: [[LOOP8]] = distinct !{[[LOOP8]], [[META1]], [[META2]]}
+; CHECK: [[LOOP9]] = distinct !{[[LOOP9]], [[META2]], [[META1]]}
+; CHECK: [[LOOP10]] = distinct !{[[LOOP10]], [[META1]], [[META2]]}
+; CHECK: [[LOOP11]] = distinct !{[[LOOP11]], [[META2]], [[META1]]}
+; CHECK: [[LOOP12]] = distinct !{[[LOOP12]], [[META1]], [[META2]]}
+; CHECK: [[LOOP13]] = distinct !{[[LOOP13]], [[META2]], [[META1]]}
+;.



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