LFTR for multiple exit loops

Teach IndVarSimply's LinearFunctionTestReplace transform to handle multiple exit loops. LFTR does two key things 1) it rewrites (all) exit tests in terms of a common IV potentially eliminating one in the process and 2) it moves any offset/indexing/f(i) style logic out of the loop.

This turns out to actually be pretty easy to implement. SCEV already has all the information we need to know what the backedge taken count is for each individual exit. (We use that when computing the BE taken count for the loop as a whole.) We basically just need to iterate through the exiting blocks and apply the existing logic with the exit specific BE taken count. (The previously landed NFC makes this super obvious.)

I chose to go ahead and apply this to all loop exits instead of only latch exits as originally proposed. After reviewing other passes, the only case I could find where LFTR form was harmful was LoopPredication. I've fixed the latch case, and guards aren't LFTRed anyways. We'll have some more work to do on the way towards widenable_conditions, but that's easily deferred.

I do want to note that I added one bit after the review.  When running tests, I saw a new failure (no idea why didn't see previously) which pointed out LFTR can rewrite a constant condition back to a loop varying one.  This was theoretically possible with a single exit, but the zero case covered it in practice.  With multiple exits, we saw this happening in practice for the eliminate-comparison.ll test case because we'd compute a ExitCount for one of the exits which was guaranteed to never actually be reached.  Since LFTR ran after simplifyAndExtend, we'd immediately turn around and undo the simplication work we'd just done.  The solution seemed obvious, so I didn't bother with another round of review.

Differential Revision: https://reviews.llvm.org/D62625

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@363883 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index 969ad50e96d134f177b83032569ba339fbabaff1..b8f3d1b9c1ba50efa1386a8d72f67595bb73e87b 100644 (file)
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -2037,15 +2037,21 @@ static ICmpInst *getLoopTest(Loop *L, BasicBlock *ExitingBB) {
   if (!LatchBlock)
     return nullptr;
 
-  BranchInst *BI = dyn_cast<BranchInst>(ExitingBB->getTerminator());
-  assert(BI && "expected exit branch");
-
+  BranchInst *BI = cast<BranchInst>(ExitingBB->getTerminator());
   return dyn_cast<ICmpInst>(BI->getCondition());
 }
 
 /// linearFunctionTestReplace policy. Return true unless we can show that the
 /// current exit test is already sufficiently canonical.
 static bool needsLFTR(Loop *L, BasicBlock *ExitingBB) {
+  // Avoid converting a constant or loop invariant test back to a runtime
+  // test.  This is critical for when SCEV's cached ExitCount is less precise
+  // than the current IR (such as after we've proven a particular exit is
+  // actually dead and thus the BE count never reaches our ExitCount.)
+  BranchInst *BI = cast<BranchInst>(ExitingBB->getTerminator());
+  if (L->isLoopInvariant(BI->getCondition()))
+    return false;
+  
   // Do LFTR to simplify the exit condition to an ICMP.
   ICmpInst *Cond = getLoopTest(L, ExitingBB);
   if (!Cond)
@@ -2247,15 +2253,12 @@ static PHINode *FindLoopCounter(Loop *L, BasicBlock *ExitingBB,
     // have originally had a concrete definition.
     if (!hasConcreteDef(Phi)) {
       // We explicitly allow unknown phis as long as they are already used by
-      // the loop test. In this case we assume that performing LFTR could not
-      // increase the number of undef users.
-      // TODO: Generalize this to allow *any* loop exit which is known to
-      // execute on each iteration
-      if (L->getExitingBlock())
-        if (ICmpInst *Cond = getLoopTest(L, ExitingBB))
-          if (Phi != getLoopPhiForCounter(Cond->getOperand(0), L) &&
-              Phi != getLoopPhiForCounter(Cond->getOperand(1), L))
-            continue;
+      // the loop exit test.  This is legal since performing LFTR could not
+      // increase the number of undef users. 
+      if (ICmpInst *Cond = getLoopTest(L, ExitingBB))
+        if (Phi != getLoopPhiForCounter(Cond->getOperand(0), L) &&
+            Phi != getLoopPhiForCounter(Cond->getOperand(1), L))
+          continue;
     }
 
     // Avoid introducing undefined behavior due to poison which didn't exist in
@@ -2701,12 +2704,8 @@ bool IndVarSimplify::run(Loop *L) {
   // If we have a trip count expression, rewrite the loop's exit condition
   // using it.  
   if (!DisableLFTR) {
-    // For the moment, we only do LFTR for single exit loops.  The code is
-    // structured as it is in the expectation of generalization to multi-exit
-    // loops in the near future.  See D62625 for context.
     SmallVector<BasicBlock*, 16> ExitingBlocks;
-    if (auto *ExitingBB = L->getExitingBlock())
-      ExitingBlocks.push_back(ExitingBB);
+    L->getExitingBlocks(ExitingBlocks);
     for (BasicBlock *ExitingBB : ExitingBlocks) {
       // Can't rewrite non-branch yet.
       if (!isa<BranchInst>(ExitingBB->getTerminator()))

diff --git a/test/Transforms/IndVarSimplify/eliminate-comparison.ll b/test/Transforms/IndVarSimplify/eliminate-comparison.ll
index 0c1a262417c832c323b5b96504b37d57dea2b015..cd639f8d731a9015cc221f2db9999d35c22c9f6a 100644 (file)
--- a/test/Transforms/IndVarSimplify/eliminate-comparison.ll
+++ b/test/Transforms/IndVarSimplify/eliminate-comparison.ll
@@ -177,8 +177,8 @@ define i32 @func_11() nounwind uwtable {
 ; CHECK-NEXT:    br label [[FORCOND:%.*]]
 ; CHECK:       forcond:
 ; CHECK-NEXT:    [[__KEY6_0:%.*]] = phi i32 [ 2, [[ENTRY:%.*]] ], [ [[TMP37:%.*]], [[NOASSERT:%.*]] ]
-; CHECK-NEXT:    [[TMP5:%.*]] = icmp ult i32 [[__KEY6_0]], 10
-; CHECK-NEXT:    br i1 [[TMP5]], label [[NOASSERT]], label [[FORCOND38_PREHEADER:%.*]]
+; CHECK-NEXT:    [[EXITCOND1:%.*]] = icmp ne i32 [[__KEY6_0]], 10
+; CHECK-NEXT:    br i1 [[EXITCOND1]], label [[NOASSERT]], label [[FORCOND38_PREHEADER:%.*]]
 ; CHECK:       forcond38.preheader:
 ; CHECK-NEXT:    br label [[FORCOND38:%.*]]
 ; CHECK:       noassert:
@@ -193,8 +193,8 @@ define i32 @func_11() nounwind uwtable {
 ; CHECK-NEXT:    unreachable
 ; CHECK:       forcond38:
 ; CHECK-NEXT:    [[__KEY8_0:%.*]] = phi i32 [ [[TMP81:%.*]], [[NOASSERT68:%.*]] ], [ 2, [[FORCOND38_PREHEADER]] ]
-; CHECK-NEXT:    [[TMP46:%.*]] = icmp ult i32 [[__KEY8_0]], 10
-; CHECK-NEXT:    br i1 [[TMP46]], label [[NOASSERT68]], label [[UNROLLEDEND:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[__KEY8_0]], 10
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[NOASSERT68]], label [[UNROLLEDEND:%.*]]
 ; CHECK:       noassert68:
 ; CHECK-NEXT:    [[TMP57:%.*]] = sdiv i32 -32768, [[__KEY8_0]]
 ; CHECK-NEXT:    [[SEXT34:%.*]] = shl i32 [[TMP57]], 16
@@ -261,8 +261,8 @@ define i32 @func_12() nounwind uwtable {
 ; CHECK-NEXT:    br label [[FORCOND:%.*]]
 ; CHECK:       forcond:
 ; CHECK-NEXT:    [[__KEY6_0:%.*]] = phi i32 [ 2, [[ENTRY:%.*]] ], [ [[TMP37:%.*]], [[NOASSERT:%.*]] ]
-; CHECK-NEXT:    [[TMP5:%.*]] = icmp ult i32 [[__KEY6_0]], 10
-; CHECK-NEXT:    br i1 [[TMP5]], label [[NOASSERT]], label [[FORCOND38_PREHEADER:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[__KEY6_0]], 10
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[NOASSERT]], label [[FORCOND38_PREHEADER:%.*]]
 ; CHECK:       forcond38.preheader:
 ; CHECK-NEXT:    br label [[FORCOND38:%.*]]
 ; CHECK:       noassert:
@@ -341,7 +341,6 @@ define void @func_13(i32* %len.ptr) {
 ; CHECK-LABEL: @func_13(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[LEN:%.*]] = load i32, i32* [[LEN_PTR:%.*]], !range !0
-; CHECK-NEXT:    [[LEN_SUB_1:%.*]] = add i32 [[LEN]], -1
 ; CHECK-NEXT:    [[LEN_IS_ZERO:%.*]] = icmp eq i32 [[LEN]], 0
 ; CHECK-NEXT:    br i1 [[LEN_IS_ZERO]], label [[LEAVE:%.*]], label [[LOOP_PREHEADER:%.*]]
 ; CHECK:       loop.preheader:
@@ -353,8 +352,8 @@ define void @func_13(i32* %len.ptr) {
 ; CHECK-NEXT:    br i1 true, label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
 ; CHECK:       be:
 ; CHECK-NEXT:    call void @side_effect()
-; CHECK-NEXT:    [[BE_COND:%.*]] = icmp ult i32 [[IV]], [[LEN_SUB_1]]
-; CHECK-NEXT:    br i1 [[BE_COND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_INC]], [[LEN]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
 ; CHECK:       leave.loopexit:
 ; CHECK-NEXT:    br label [[LEAVE]]
 ; CHECK:       leave:
@@ -386,7 +385,6 @@ define void @func_14(i32* %len.ptr) {
 ; CHECK-LABEL: @func_14(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[LEN:%.*]] = load i32, i32* [[LEN_PTR:%.*]], !range !0
-; CHECK-NEXT:    [[LEN_SUB_1:%.*]] = add i32 [[LEN]], -1
 ; CHECK-NEXT:    [[LEN_IS_ZERO:%.*]] = icmp eq i32 [[LEN]], 0
 ; CHECK-NEXT:    [[LEN_IS_INT_MIN:%.*]] = icmp eq i32 [[LEN]], -2147483648
 ; CHECK-NEXT:    [[NO_ENTRY:%.*]] = or i1 [[LEN_IS_ZERO]], [[LEN_IS_INT_MIN]]
@@ -400,8 +398,8 @@ define void @func_14(i32* %len.ptr) {
 ; CHECK-NEXT:    br i1 true, label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
 ; CHECK:       be:
 ; CHECK-NEXT:    call void @side_effect()
-; CHECK-NEXT:    [[BE_COND:%.*]] = icmp slt i32 [[IV]], [[LEN_SUB_1]]
-; CHECK-NEXT:    br i1 [[BE_COND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_INC]], [[LEN]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
 ; CHECK:       leave.loopexit:
 ; CHECK-NEXT:    br label [[LEAVE]]
 ; CHECK:       leave:
@@ -447,8 +445,8 @@ define void @func_15(i32* %len.ptr) {
 ; CHECK-NEXT:    br i1 true, label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
 ; CHECK:       be:
 ; CHECK-NEXT:    call void @side_effect()
-; CHECK-NEXT:    [[BE_COND:%.*]] = icmp ult i32 [[IV]], [[LEN]]
-; CHECK-NEXT:    br i1 [[BE_COND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_INC]], [[LEN_ADD_1]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
 ; CHECK:       leave.loopexit:
 ; CHECK-NEXT:    br label [[LEAVE]]
 ; CHECK:       leave:
@@ -486,6 +484,7 @@ define void @func_16(i32* %len.ptr) {
 ; CHECK-NEXT:    [[ENTRY_COND:%.*]] = and i1 [[ENTRY_COND_0]], [[ENTRY_COND_1]]
 ; CHECK-NEXT:    br i1 [[ENTRY_COND]], label [[LOOP_PREHEADER:%.*]], label [[LEAVE:%.*]]
 ; CHECK:       loop.preheader:
+; CHECK-NEXT:    [[TMP0:%.*]] = add nuw nsw i32 [[LEN]], 1
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ [[IV_INC:%.*]], [[BE:%.*]] ], [ 0, [[LOOP_PREHEADER]] ]
@@ -494,8 +493,8 @@ define void @func_16(i32* %len.ptr) {
 ; CHECK-NEXT:    br i1 true, label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
 ; CHECK:       be:
 ; CHECK-NEXT:    call void @side_effect()
-; CHECK-NEXT:    [[BE_COND:%.*]] = icmp ult i32 [[IV]], [[LEN]]
-; CHECK-NEXT:    br i1 [[BE_COND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_INC]], [[TMP0]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
 ; CHECK:       leave.loopexit:
 ; CHECK-NEXT:    br label [[LEAVE]]
 ; CHECK:       leave:
@@ -656,8 +655,8 @@ define void @func_19(i32* %length.ptr) {
 ; CHECK-NEXT:    br i1 true, label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
 ; CHECK:       be:
 ; CHECK-NEXT:    call void @side_effect()
-; CHECK-NEXT:    [[BE_COND:%.*]] = icmp ult i32 [[IV_INC]], [[LENGTH]]
-; CHECK-NEXT:    br i1 [[BE_COND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_INC]], [[LENGTH]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
 ; CHECK:       leave.loopexit:
 ; CHECK-NEXT:    br label [[LEAVE]]
 ; CHECK:       leave:
@@ -696,8 +695,8 @@ define void @func_20(i32* %length.ptr) {
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ [[IV_INC:%.*]], [[BE:%.*]] ], [ 0, [[LOOP_PREHEADER]] ]
 ; CHECK-NEXT:    [[IV_INC]] = add nuw nsw i32 [[IV]], 1
-; CHECK-NEXT:    [[RANGE_CHECK:%.*]] = icmp ult i32 [[IV]], [[LENGTH]]
-; CHECK-NEXT:    br i1 [[RANGE_CHECK]], label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV]], [[LENGTH]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
 ; CHECK:       be:
 ; CHECK-NEXT:    call void @side_effect()
 ; CHECK-NEXT:    [[BE_COND:%.*]] = icmp slt i32 [[IV_INC]], [[LENGTH]]
@@ -744,8 +743,8 @@ define void @func_21(i32* %length.ptr) {
 ; CHECK-NEXT:    br i1 true, label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
 ; CHECK:       be:
 ; CHECK-NEXT:    call void @side_effect()
-; CHECK-NEXT:    [[BE_COND:%.*]] = icmp slt i32 [[IV_INC]], [[LIM]]
-; CHECK-NEXT:    br i1 [[BE_COND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_INC]], [[LIM]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
 ; CHECK:       leave.loopexit:
 ; CHECK-NEXT:    br label [[LEAVE]]
 ; CHECK:       leave:
@@ -778,7 +777,6 @@ define void @func_22(i32* %length.ptr) {
 ; CHECK-LABEL: @func_22(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[LENGTH:%.*]] = load i32, i32* [[LENGTH_PTR:%.*]], !range !0
-; CHECK-NEXT:    [[LIM:%.*]] = sub i32 [[LENGTH]], 1
 ; CHECK-NEXT:    [[ENTRY_COND:%.*]] = icmp sgt i32 [[LENGTH]], 1
 ; CHECK-NEXT:    br i1 [[ENTRY_COND]], label [[LOOP_PREHEADER:%.*]], label [[LEAVE:%.*]]
 ; CHECK:       loop.preheader:
@@ -789,8 +787,8 @@ define void @func_22(i32* %length.ptr) {
 ; CHECK-NEXT:    br i1 true, label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
 ; CHECK:       be:
 ; CHECK-NEXT:    call void @side_effect()
-; CHECK-NEXT:    [[BE_COND:%.*]] = icmp sle i32 [[IV_INC]], [[LIM]]
-; CHECK-NEXT:    br i1 [[BE_COND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_INC]], [[LENGTH]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
 ; CHECK:       leave.loopexit:
 ; CHECK-NEXT:    br label [[LEAVE]]
 ; CHECK:       leave:
@@ -831,8 +829,8 @@ define void @func_23(i32* %length.ptr) {
 ; CHECK-NEXT:    br i1 true, label [[BE]], label [[LEAVE_LOOPEXIT:%.*]]
 ; CHECK:       be:
 ; CHECK-NEXT:    call void @side_effect()
-; CHECK-NEXT:    [[BE_COND:%.*]] = icmp ult i32 [[IV_INC]], [[LENGTH]]
-; CHECK-NEXT:    br i1 [[BE_COND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_INC]], [[LENGTH]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[LEAVE_LOOPEXIT]]
 ; CHECK:       leave.loopexit:
 ; CHECK-NEXT:    br label [[LEAVE]]
 ; CHECK:       leave:

diff --git a/test/Transforms/IndVarSimplify/lftr-multi-exit.ll b/test/Transforms/IndVarSimplify/lftr-multi-exit.ll
index a45f26b88a951209a8a8602a202d1e192fa0e17e..b8555ede96633ac1dd2173f1664bbd2ea3cee6e8 100644 (file)
--- a/test/Transforms/IndVarSimplify/lftr-multi-exit.ll
+++ b/test/Transforms/IndVarSimplify/lftr-multi-exit.ll
@@ -15,13 +15,13 @@ define void @analyzeable_early_exit(i32 %n) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
-; CHECK-NEXT:    [[EARLYCND:%.*]] = icmp ult i32 [[IV]], [[N:%.*]]
-; CHECK-NEXT:    br i1 [[EARLYCND]], label [[LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LATCH]], label [[EXIT:%.*]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
 ; CHECK-NEXT:    store i32 [[IV]], i32* @A
-; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[IV_NEXT]], 1000
-; CHECK-NEXT:    br i1 [[C]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    [[EXITCOND1:%.*]] = icmp ne i32 [[IV_NEXT]], 1000
+; CHECK-NEXT:    br i1 [[EXITCOND1]], label [[LOOP]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -55,8 +55,8 @@ define void @unanalyzeable_early_exit() {
 ; CHECK:       latch:
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
 ; CHECK-NEXT:    store i32 [[IV]], i32* @A
-; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[IV_NEXT]], 1000
-; CHECK-NEXT:    br i1 [[C]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_NEXT]], 1000
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -86,17 +86,17 @@ define void @multiple_early_exits(i32 %n, i32 %m) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
-; CHECK-NEXT:    [[EARLYCND:%.*]] = icmp ult i32 [[IV]], [[N:%.*]]
-; CHECK-NEXT:    br i1 [[EARLYCND]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
 ; CHECK:       continue:
 ; CHECK-NEXT:    store volatile i32 [[IV]], i32* @A
-; CHECK-NEXT:    [[EARLYCND2:%.*]] = icmp ult i32 [[IV]], [[M:%.*]]
-; CHECK-NEXT:    br i1 [[EARLYCND2]], label [[LATCH]], label [[EXIT]]
+; CHECK-NEXT:    [[EXITCOND1:%.*]] = icmp ne i32 [[IV]], [[M:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND1]], label [[LATCH]], label [[EXIT]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
 ; CHECK-NEXT:    store volatile i32 [[IV]], i32* @A
-; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[IV_NEXT]], 1000
-; CHECK-NEXT:    br i1 [[C]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    [[EXITCOND2:%.*]] = icmp ne i32 [[IV_NEXT]], 1000
+; CHECK-NEXT:    br i1 [[EXITCOND2]], label [[LOOP]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -138,8 +138,8 @@ define void @compound_early_exit(i32 %n, i32 %m) {
 ; CHECK:       latch:
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
 ; CHECK-NEXT:    store volatile i32 [[IV]], i32* @A
-; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[IV_NEXT]], 1000
-; CHECK-NEXT:    br i1 [[C]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV_NEXT]], 1000
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOP]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -170,8 +170,8 @@ define void @unanalyzeable_latch(i32 %n) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
-; CHECK-NEXT:    [[EARLYCND:%.*]] = icmp ult i32 [[IV]], [[N:%.*]]
-; CHECK-NEXT:    br i1 [[EARLYCND]], label [[LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LATCH]], label [[EXIT:%.*]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1
 ; CHECK-NEXT:    store i32 [[IV]], i32* @A
@@ -240,12 +240,12 @@ define void @no_latch_exit(i32 %n, i32 %m) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
-; CHECK-NEXT:    [[EARLYCND:%.*]] = icmp ult i32 [[IV]], [[N:%.*]]
-; CHECK-NEXT:    br i1 [[EARLYCND]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
 ; CHECK:       continue:
 ; CHECK-NEXT:    store volatile i32 [[IV]], i32* @A
-; CHECK-NEXT:    [[EARLYCND2:%.*]] = icmp ult i32 [[IV]], [[M:%.*]]
-; CHECK-NEXT:    br i1 [[EARLYCND2]], label [[LATCH]], label [[EXIT]]
+; CHECK-NEXT:    [[EXITCOND1:%.*]] = icmp ne i32 [[IV]], [[M:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND1]], label [[LATCH]], label [[EXIT]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    store volatile i32 [[IV]], i32* @A
 ; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1
@@ -283,15 +283,13 @@ define void @combine_ivs(i32 %n) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
-; CHECK-NEXT:    [[IV2:%.*]] = phi i32 [ 1, [[ENTRY]] ], [ [[IV2_NEXT:%.*]], [[LATCH]] ]
-; CHECK-NEXT:    [[EARLYCND:%.*]] = icmp ult i32 [[IV]], [[N:%.*]]
-; CHECK-NEXT:    br i1 [[EARLYCND]], label [[LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LATCH]], label [[EXIT:%.*]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
-; CHECK-NEXT:    [[IV2_NEXT]] = add nuw nsw i32 [[IV2]], 1
 ; CHECK-NEXT:    store volatile i32 [[IV]], i32* @A
-; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[IV2_NEXT]], 1000
-; CHECK-NEXT:    br i1 [[C]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    [[EXITCOND1:%.*]] = icmp ne i32 [[IV_NEXT]], 999
+; CHECK-NEXT:    br i1 [[EXITCOND1]], label [[LOOP]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -322,15 +320,13 @@ define void @combine_ivs2(i32 %n) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
-; CHECK-NEXT:    [[IV2:%.*]] = phi i32 [ 1000, [[ENTRY]] ], [ [[IV2_NEXT:%.*]], [[LATCH]] ]
-; CHECK-NEXT:    [[EARLYCND:%.*]] = icmp ult i32 [[IV]], [[N:%.*]]
-; CHECK-NEXT:    br i1 [[EARLYCND]], label [[LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LATCH]], label [[EXIT:%.*]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
-; CHECK-NEXT:    [[IV2_NEXT]] = sub nuw nsw i32 [[IV2]], 1
 ; CHECK-NEXT:    store volatile i32 [[IV]], i32* @A
-; CHECK-NEXT:    [[C:%.*]] = icmp ugt i32 [[IV2_NEXT]], 0
-; CHECK-NEXT:    br i1 [[C]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    [[EXITCOND1:%.*]] = icmp ne i32 [[IV_NEXT]], 1000
+; CHECK-NEXT:    br i1 [[EXITCOND1]], label [[LOOP]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -362,14 +358,13 @@ define void @simplify_exit_test(i32 %n) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
-; CHECK-NEXT:    [[EARLYCND:%.*]] = icmp ult i32 [[IV]], [[N:%.*]]
-; CHECK-NEXT:    br i1 [[EARLYCND]], label [[LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[IV]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LATCH]], label [[EXIT:%.*]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
-; CHECK-NEXT:    [[FX:%.*]] = shl i32 [[IV]], 4
 ; CHECK-NEXT:    store volatile i32 [[IV]], i32* @A
-; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[FX]], 1024
-; CHECK-NEXT:    br i1 [[C]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    [[EXITCOND1:%.*]] = icmp ne i32 [[IV_NEXT]], 65
+; CHECK-NEXT:    br i1 [[EXITCOND1]], label [[LOOP]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;