[LoopUnroll] Only peel if a predicate becomes known in the loop body.

If a predicate does not become known after peeling, peeling is unlikely
to be beneficial.

Reviewers: mcrosier, efriedma, mkazantsev, junbuml

Reviewed By: mkazantsev

Differential Revision: https://reviews.llvm.org/D44983

llvm-svn: 330250

diff --git a/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp b/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
index 0d2e710..555e328 100644 (file)
--- a/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
@@ -190,14 +190,25 @@ static unsigned countToEliminateCompares(Loop &L, unsigned MaxPeelCount,
 
     const SCEVAddRecExpr *LeftAR = cast<SCEVAddRecExpr>(LeftSCEV);
 
-    // Avoid huge SCEV computations in the loop below and make sure we only
-    // consider AddRecs of the loop we are trying to peel.
-    if (!LeftAR->isAffine() || LeftAR->getLoop() != &L)
+    // Avoid huge SCEV computations in the loop below, make sure we only
+    // consider AddRecs of the loop we are trying to peel and avoid
+    // non-monotonic predicates, as we will not be able to simplify the loop
+    // body.
+    // FIXME: For the non-monotonic predicates ICMP_EQ and ICMP_NE we can
+    //        simplify the loop, if we peel 1 additional iteration, if there
+    //        is no wrapping.
+    bool Increasing;
+    if (!LeftAR->isAffine() || LeftAR->getLoop() != &L ||
+        !SE.isMonotonicPredicate(LeftAR, Pred, Increasing))
       continue;
+    (void)Increasing;
+
+    // Check if extending the current DesiredPeelCount lets us evaluate Pred
+    // or !Pred in the loop body statically.
+    unsigned NewPeelCount = DesiredPeelCount;
 
-    // Check if extending DesiredPeelCount lets us evaluate Pred.
     const SCEV *IterVal = LeftAR->evaluateAtIteration(
-        SE.getConstant(LeftSCEV->getType(), DesiredPeelCount), SE);
+        SE.getConstant(LeftSCEV->getType(), NewPeelCount), SE);
 
     // If the original condition is not known, get the negated predicate
     // (which holds on the else branch) and check if it is known. This allows
@@ -206,11 +217,18 @@ static unsigned countToEliminateCompares(Loop &L, unsigned MaxPeelCount,
       Pred = ICmpInst::getInversePredicate(Pred);
 
     const SCEV *Step = LeftAR->getStepRecurrence(SE);
-    while (DesiredPeelCount < MaxPeelCount &&
+    while (NewPeelCount < MaxPeelCount &&
            SE.isKnownPredicate(Pred, IterVal, RightSCEV)) {
       IterVal = SE.getAddExpr(IterVal, Step);
-      DesiredPeelCount++;
+      NewPeelCount++;
     }
+
+    // Only peel the loop if the monotonic predicate !Pred becomes known in the
+    // first iteration of the loop body after peeling.
+    if (NewPeelCount > DesiredPeelCount &&
+        SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), IterVal,
+                            RightSCEV))
+      DesiredPeelCount = NewPeelCount;
   }
 
   return DesiredPeelCount;

diff --git a/llvm/test/Transforms/LoopUnroll/peel-loop-conditions.ll b/llvm/test/Transforms/LoopUnroll/peel-loop-conditions.ll
index 01dbc04..98570c0 100644 (file)
--- a/llvm/test/Transforms/LoopUnroll/peel-loop-conditions.ll
+++ b/llvm/test/Transforms/LoopUnroll/peel-loop-conditions.ll
@@ -338,114 +338,23 @@ for.end:
   ret void
 }
 
-; Test that we respect MaxPeelCount
+; Test that we only peel off iterations if it simplifies a condition in the
+; loop body after peeling at most MaxPeelCount iterations.
 define void @test4(i32 %k) {
 ; CHECK-LABEL: @test4(
 ; CHECK-NEXT:  for.body.lr.ph:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL_BEGIN:%.*]]
-; CHECK:       for.body.peel.begin:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL:%.*]]
-; CHECK:       for.body.peel:
-; CHECK-NEXT:    [[CMP1_PEEL:%.*]] = icmp ugt i32 0, 9999
-; CHECK-NEXT:    br i1 [[CMP1_PEEL]], label [[IF_THEN_PEEL:%.*]], label [[FOR_INC_PEEL:%.*]]
-; CHECK:       if.then.peel:
-; CHECK-NEXT:    call void @f1()
-; CHECK-NEXT:    br label [[FOR_INC_PEEL]]
-; CHECK:       for.inc.peel:
-; CHECK-NEXT:    [[INC_PEEL:%.*]] = add nsw i32 0, 1
-; CHECK-NEXT:    [[CMP_PEEL:%.*]] = icmp slt i32 [[INC_PEEL]], [[K:%.*]]
-; CHECK-NEXT:    br i1 [[CMP_PEEL]], label [[FOR_BODY_PEEL_NEXT:%.*]], label [[FOR_END:%.*]]
-; CHECK:       for.body.peel.next:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL2:%.*]]
-; CHECK:       for.body.peel2:
-; CHECK-NEXT:    [[CMP1_PEEL3:%.*]] = icmp ugt i32 [[INC_PEEL]], 9999
-; CHECK-NEXT:    br i1 [[CMP1_PEEL3]], label [[IF_THEN_PEEL4:%.*]], label [[FOR_INC_PEEL5:%.*]]
-; CHECK:       if.then.peel4:
-; CHECK-NEXT:    call void @f1()
-; CHECK-NEXT:    br label [[FOR_INC_PEEL5]]
-; CHECK:       for.inc.peel5:
-; CHECK-NEXT:    [[INC_PEEL6:%.*]] = add nsw i32 [[INC_PEEL]], 1
-; CHECK-NEXT:    [[CMP_PEEL7:%.*]] = icmp slt i32 [[INC_PEEL6]], [[K]]
-; CHECK-NEXT:    br i1 [[CMP_PEEL7]], label [[FOR_BODY_PEEL_NEXT1:%.*]], label [[FOR_END]]
-; CHECK:       for.body.peel.next1:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL9:%.*]]
-; CHECK:       for.body.peel9:
-; CHECK-NEXT:    [[CMP1_PEEL10:%.*]] = icmp ugt i32 [[INC_PEEL6]], 9999
-; CHECK-NEXT:    br i1 [[CMP1_PEEL10]], label [[IF_THEN_PEEL11:%.*]], label [[FOR_INC_PEEL12:%.*]]
-; CHECK:       if.then.peel11:
-; CHECK-NEXT:    call void @f1()
-; CHECK-NEXT:    br label [[FOR_INC_PEEL12]]
-; CHECK:       for.inc.peel12:
-; CHECK-NEXT:    [[INC_PEEL13:%.*]] = add nsw i32 [[INC_PEEL6]], 1
-; CHECK-NEXT:    [[CMP_PEEL14:%.*]] = icmp slt i32 [[INC_PEEL13]], [[K]]
-; CHECK-NEXT:    br i1 [[CMP_PEEL14]], label [[FOR_BODY_PEEL_NEXT8:%.*]], label [[FOR_END]]
-; CHECK:       for.body.peel.next8:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL16:%.*]]
-; CHECK:       for.body.peel16:
-; CHECK-NEXT:    [[CMP1_PEEL17:%.*]] = icmp ugt i32 [[INC_PEEL13]], 9999
-; CHECK-NEXT:    br i1 [[CMP1_PEEL17]], label [[IF_THEN_PEEL18:%.*]], label [[FOR_INC_PEEL19:%.*]]
-; CHECK:       if.then.peel18:
-; CHECK-NEXT:    call void @f1()
-; CHECK-NEXT:    br label [[FOR_INC_PEEL19]]
-; CHECK:       for.inc.peel19:
-; CHECK-NEXT:    [[INC_PEEL20:%.*]] = add nsw i32 [[INC_PEEL13]], 1
-; CHECK-NEXT:    [[CMP_PEEL21:%.*]] = icmp slt i32 [[INC_PEEL20]], [[K]]
-; CHECK-NEXT:    br i1 [[CMP_PEEL21]], label [[FOR_BODY_PEEL_NEXT15:%.*]], label [[FOR_END]]
-; CHECK:       for.body.peel.next15:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL23:%.*]]
-; CHECK:       for.body.peel23:
-; CHECK-NEXT:    [[CMP1_PEEL24:%.*]] = icmp ugt i32 [[INC_PEEL20]], 9999
-; CHECK-NEXT:    br i1 [[CMP1_PEEL24]], label [[IF_THEN_PEEL25:%.*]], label [[FOR_INC_PEEL26:%.*]]
-; CHECK:       if.then.peel25:
-; CHECK-NEXT:    call void @f1()
-; CHECK-NEXT:    br label [[FOR_INC_PEEL26]]
-; CHECK:       for.inc.peel26:
-; CHECK-NEXT:    [[INC_PEEL27:%.*]] = add nsw i32 [[INC_PEEL20]], 1
-; CHECK-NEXT:    [[CMP_PEEL28:%.*]] = icmp slt i32 [[INC_PEEL27]], [[K]]
-; CHECK-NEXT:    br i1 [[CMP_PEEL28]], label [[FOR_BODY_PEEL_NEXT22:%.*]], label [[FOR_END]]
-; CHECK:       for.body.peel.next22:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL30:%.*]]
-; CHECK:       for.body.peel30:
-; CHECK-NEXT:    [[CMP1_PEEL31:%.*]] = icmp ugt i32 [[INC_PEEL27]], 9999
-; CHECK-NEXT:    br i1 [[CMP1_PEEL31]], label [[IF_THEN_PEEL32:%.*]], label [[FOR_INC_PEEL33:%.*]]
-; CHECK:       if.then.peel32:
-; CHECK-NEXT:    call void @f1()
-; CHECK-NEXT:    br label [[FOR_INC_PEEL33]]
-; CHECK:       for.inc.peel33:
-; CHECK-NEXT:    [[INC_PEEL34:%.*]] = add nsw i32 [[INC_PEEL27]], 1
-; CHECK-NEXT:    [[CMP_PEEL35:%.*]] = icmp slt i32 [[INC_PEEL34]], [[K]]
-; CHECK-NEXT:    br i1 [[CMP_PEEL35]], label [[FOR_BODY_PEEL_NEXT29:%.*]], label [[FOR_END]]
-; CHECK:       for.body.peel.next29:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL37:%.*]]
-; CHECK:       for.body.peel37:
-; CHECK-NEXT:    [[CMP1_PEEL38:%.*]] = icmp ugt i32 [[INC_PEEL34]], 9999
-; CHECK-NEXT:    br i1 [[CMP1_PEEL38]], label [[IF_THEN_PEEL39:%.*]], label [[FOR_INC_PEEL40:%.*]]
-; CHECK:       if.then.peel39:
-; CHECK-NEXT:    call void @f1()
-; CHECK-NEXT:    br label [[FOR_INC_PEEL40]]
-; CHECK:       for.inc.peel40:
-; CHECK-NEXT:    [[INC_PEEL41:%.*]] = add nsw i32 [[INC_PEEL34]], 1
-; CHECK-NEXT:    [[CMP_PEEL42:%.*]] = icmp slt i32 [[INC_PEEL41]], [[K]]
-; CHECK-NEXT:    br i1 [[CMP_PEEL42]], label [[FOR_BODY_PEEL_NEXT36:%.*]], label [[FOR_END]]
-; CHECK:       for.body.peel.next36:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL_NEXT43:%.*]]
-; CHECK:       for.body.peel.next43:
-; CHECK-NEXT:    br label [[FOR_BODY_LR_PH_PEEL_NEWPH:%.*]]
-; CHECK:       for.body.lr.ph.peel.newph:
 ; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
 ; CHECK:       for.body:
-; CHECK-NEXT:    [[I_05:%.*]] = phi i32 [ [[INC_PEEL41]], [[FOR_BODY_LR_PH_PEEL_NEWPH]] ], [ [[INC:%.*]], [[FOR_INC:%.*]] ]
+; CHECK-NEXT:    [[I_05:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH:%.*]] ], [ [[INC:%.*]], [[FOR_INC:%.*]] ]
 ; CHECK-NEXT:    [[CMP1:%.*]] = icmp ugt i32 [[I_05]], 9999
 ; CHECK-NEXT:    br i1 [[CMP1]], label [[IF_THEN:%.*]], label [[FOR_INC]]
 ; CHECK:       if.then:
 ; CHECK-NEXT:    call void @f1()
 ; CHECK-NEXT:    br label [[FOR_INC]]
 ; CHECK:       for.inc:
-; CHECK-NEXT:    [[INC]] = add nuw nsw i32 [[I_05]], 1
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[INC]], [[K]]
-; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END_LOOPEXIT:%.*]], !llvm.loop !4
-; CHECK:       for.end.loopexit:
-; CHECK-NEXT:    br label [[FOR_END]]
+; CHECK-NEXT:    [[INC]] = add nsw i32 [[I_05]], 1
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[INC]], [[K:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END:%.*]]
 ; CHECK:       for.end:
 ; CHECK-NEXT:    ret void
 ;
@@ -535,36 +444,18 @@ for.end:
   ret void
 }
 
+; In this test, the condition involves 2 AddRecs. Without evaluating both
+; AddRecs, we cannot prove that the condition becomes known in the loop body
+; after peeling.
 define void @test6(i32 %k) {
 ; CHECK-LABEL: @test6(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL_BEGIN:%.*]]
-; CHECK:       for.body.peel.begin:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL:%.*]]
-; CHECK:       for.body.peel:
-; CHECK-NEXT:    [[CMP1_PEEL:%.*]] = icmp ult i32 0, 4
-; CHECK-NEXT:    br i1 [[CMP1_PEEL]], label [[IF_THEN_PEEL:%.*]], label [[IF_ELSE_PEEL:%.*]]
-; CHECK:       if.else.peel:
-; CHECK-NEXT:    call void @f2()
-; CHECK-NEXT:    br label [[FOR_INC_PEEL:%.*]]
-; CHECK:       if.then.peel:
-; CHECK-NEXT:    call void @f1()
-; CHECK-NEXT:    br label [[FOR_INC_PEEL]]
-; CHECK:       for.inc.peel:
-; CHECK-NEXT:    [[INC_PEEL:%.*]] = add nsw i32 0, 2
-; CHECK-NEXT:    [[J_INC_PEEL:%.*]] = add nsw i32 4, 1
-; CHECK-NEXT:    [[CMP_PEEL:%.*]] = icmp slt i32 [[INC_PEEL]], [[K:%.*]]
-; CHECK-NEXT:    br i1 [[CMP_PEEL]], label [[FOR_BODY_PEEL_NEXT:%.*]], label [[FOR_END:%.*]]
-; CHECK:       for.body.peel.next:
-; CHECK-NEXT:    br label [[FOR_BODY_PEEL_NEXT1:%.*]]
-; CHECK:       for.body.peel.next1:
-; CHECK-NEXT:    br label [[ENTRY_PEEL_NEWPH:%.*]]
-; CHECK:       entry.peel.newph:
 ; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
 ; CHECK:       for.body:
-; CHECK-NEXT:    [[I_05:%.*]] = phi i32 [ [[INC_PEEL]], [[ENTRY_PEEL_NEWPH]] ], [ [[INC:%.*]], [[FOR_INC:%.*]] ]
-; CHECK-NEXT:    [[J:%.*]] = phi i32 [ [[INC_PEEL]], [[ENTRY_PEEL_NEWPH]] ], [ [[INC]], [[FOR_INC]] ]
-; CHECK-NEXT:    br i1 false, label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK-NEXT:    [[I_05:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[FOR_INC:%.*]] ]
+; CHECK-NEXT:    [[J:%.*]] = phi i32 [ 4, [[ENTRY]] ], [ [[J_INC:%.*]], [[FOR_INC]] ]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp ult i32 [[I_05]], [[J]]
+; CHECK-NEXT:    br i1 [[CMP1]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
 ; CHECK:       if.then:
 ; CHECK-NEXT:    call void @f1()
 ; CHECK-NEXT:    br label [[FOR_INC]]
@@ -572,11 +463,10 @@ define void @test6(i32 %k) {
 ; CHECK-NEXT:    call void @f2()
 ; CHECK-NEXT:    br label [[FOR_INC]]
 ; CHECK:       for.inc:
-; CHECK-NEXT:    [[INC]] = add nuw nsw i32 [[I_05]], 2
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[INC]], [[K]]
-; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END_LOOPEXIT:%.*]], !llvm.loop !5
-; CHECK:       for.end.loopexit:
-; CHECK-NEXT:    br label [[FOR_END]]
+; CHECK-NEXT:    [[INC]] = add nsw i32 [[I_05]], 2
+; CHECK-NEXT:    [[J_INC]] = add nsw i32 [[J]], 1
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[INC]], [[K:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END:%.*]]
 ; CHECK:       for.end:
 ; CHECK-NEXT:    ret void
 ;
@@ -585,7 +475,7 @@ entry:
 
 for.body:
   %i.05 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
-  %j = phi i32 [ 4, %entry ], [ %inc, %for.inc ]
+  %j = phi i32 [ 4, %entry ], [ %j.inc, %for.inc ]
   %cmp1 = icmp ult i32 %i.05, %j
   br i1 %cmp1, label %if.then, label %if.else
 
@@ -606,3 +496,126 @@ for.inc:
 for.end:
   ret void
 }
+
+define void @test7(i32 %k) {
+; FIXME: Could simplify loop body by peeling one additional iteration after
+;        i != 3 becomes false
+; CHECK-LABEL: @test7(
+; CHECK-NEXT:  for.body.lr.ph:
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[I_05:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH:%.*]] ], [ [[INC:%.*]], [[FOR_INC:%.*]] ]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp ne i32 [[I_05]], 3
+; CHECK-NEXT:    br i1 [[CMP1]], label [[IF_THEN:%.*]], label [[FOR_INC]]
+; CHECK:       if.then:
+; CHECK-NEXT:    call void @f1()
+; CHECK-NEXT:    br label [[FOR_INC]]
+; CHECK:       for.inc:
+; CHECK-NEXT:    [[INC]] = add nsw i32 [[I_05]], 1
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[INC]], [[K:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+for.body.lr.ph:
+  br label %for.body
+
+for.body:
+  %i.05 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.inc ]
+  %cmp1 = icmp ne i32 %i.05, 3
+  br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:
+  call void @f1()
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %i.05, 1
+  %cmp = icmp slt i32 %inc, %k
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:
+  ret void
+}
+
+define void @test8(i32 %k) {
+; FIXME: Could simplify loop body by peeling one additional iteration after
+;        i == 3 becomes true.
+; CHECK-LABEL: @test8(
+; CHECK-NEXT:  for.body.lr.ph:
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[I_05:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH:%.*]] ], [ [[INC:%.*]], [[FOR_INC:%.*]] ]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i32 [[I_05]], 3
+; CHECK-NEXT:    br i1 [[CMP1]], label [[IF_THEN:%.*]], label [[FOR_INC]]
+; CHECK:       if.then:
+; CHECK-NEXT:    call void @f1()
+; CHECK-NEXT:    br label [[FOR_INC]]
+; CHECK:       for.inc:
+; CHECK-NEXT:    [[INC]] = add nsw i32 [[I_05]], 1
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[INC]], [[K:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+for.body.lr.ph:
+  br label %for.body
+
+for.body:
+  %i.05 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.inc ]
+  %cmp1 = icmp eq i32 %i.05, 3
+  br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:
+  call void @f1()
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %i.05, 1
+  %cmp = icmp slt i32 %inc, %k
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:
+  ret void
+}
+
+; Comparison with non-monotonic predicate due to possible wrapping, loop
+; body cannot be simplified.
+define void @test9(i32 %k) {
+; CHECK-LABEL: @test9(
+; CHECK-NEXT:  for.body.lr.ph:
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[I_05:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH:%.*]] ], [ [[INC:%.*]], [[FOR_INC:%.*]] ]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i32 [[I_05]], 3
+; CHECK-NEXT:    br i1 [[CMP1]], label [[IF_THEN:%.*]], label [[FOR_INC]]
+; CHECK:       if.then:
+; CHECK-NEXT:    call void @f1()
+; CHECK-NEXT:    br label [[FOR_INC]]
+; CHECK:       for.inc:
+; CHECK-NEXT:    [[INC]] = add i32 [[I_05]], 1
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[INC]], [[K:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+for.body.lr.ph:
+  br label %for.body
+
+for.body:
+  %i.05 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.inc ]
+  %cmp1 = icmp slt i32 %i.05, 3
+  br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:
+  call void @f1()
+  br label %for.inc
+
+for.inc:
+  %inc = add i32 %i.05, 1
+  %cmp = icmp slt i32 %inc, %k
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:
+  ret void
+}