Index: lib/Transforms/Scalar/CallSiteSplitting.cpp
===================================================================
--- lib/Transforms/Scalar/CallSiteSplitting.cpp
+++ lib/Transforms/Scalar/CallSiteSplitting.cpp
@@ -406,7 +406,13 @@
   bool Changed = false;
   for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE;) {
     BasicBlock &BB = *BI++;
-    for (BasicBlock::iterator II = BB.begin(), IE = BB.end(); II != IE;) {
+    auto II = BB.getFirstNonPHIOrDbg()->getIterator();
+    auto IE = BB.getTerminator()->getIterator();
+    // Iterate until we reach the terminator instruction. tryToSplitCallSite
+    // can replace BB's terminator in case BB is a successor of itself. In that
+    // case, IE will be invalidated and we also have to check the current
+    // terminator.
+    while (II != IE && &*II != BB.getTerminator()) {
       Instruction *I = &*II++;
       CallSite CS(cast<Value>(I));
       if (!CS || isa<IntrinsicInst>(I) || isInstructionTriviallyDead(I, &TLI))
Index: test/Transforms/CallSiteSplitting/split-loop.ll
===================================================================
--- /dev/null
+++ test/Transforms/CallSiteSplitting/split-loop.ll
@@ -0,0 +1,90 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -callsite-splitting -simplifycfg < %s | FileCheck %s
+
+define i16 @test1() {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 undef, i16 1, i16 0
+; CHECK-NEXT:    call void @callee(i16 0)
+; CHECK-NEXT:    br label [[FOR_COND12:%.*]]
+; CHECK:       for.cond12:
+; CHECK-NEXT:    call void @callee(i16 [[SPEC_SELECT]])
+; CHECK-NEXT:    br label [[FOR_COND12]]
+;
+entry:
+  %spec.select = select i1 undef, i16 1, i16 0
+  %tobool18 = icmp ne i16 %spec.select, 0
+  br i1 %tobool18, label %for.cond12.us, label %for.cond12
+
+for.cond12.us:
+  unreachable
+
+for.cond12:
+  call void @callee(i16 %spec.select)
+  br label %for.cond12
+}
+
+define i16 @test2() {
+; CHECK-LABEL: @test2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[S:%.*]] = select i1 undef, i16 1, i16 0
+; CHECK-NEXT:    call void @callee(i16 0)
+; CHECK-NEXT:    br label [[FOR_COND12:%.*]]
+; CHECK:       for.cond12:
+; CHECK-NEXT:    [[ADD:%.*]] = add i16 [[S]], 10
+; CHECK-NEXT:    [[ADD2:%.*]] = add i16 [[S]], 10
+; CHECK-NEXT:    call void @callee(i16 [[S]])
+; CHECK-NEXT:    br label [[FOR_COND12]]
+;
+entry:
+  %s= select i1 undef, i16 1, i16 0
+  %tobool18 = icmp ne i16 %s, 0
+  br i1 %tobool18, label %for.cond12.us, label %for.cond12
+
+for.cond12.us:
+  unreachable
+
+for.cond12:
+  call void @callee(i16 %s)
+  %add = add i16 %s, 10
+  %add2 = add i16 %s, 10
+  br label %for.cond12
+}
+
+define i16 @test3() {
+; CHECK-LABEL: @test3(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[S:%.*]] = select i1 undef, i16 1, i16 0
+; CHECK-NEXT:    call void @callee(i16 0)
+; CHECK-NEXT:    br label [[FOR_COND12:%.*]]
+; CHECK:       for.cond12:
+; CHECK-NEXT:    [[ADD:%.*]] = add i16 [[S]], 10
+; CHECK-NEXT:    [[ADD2:%.*]] = add i16 [[ADD]], 10
+; CHECK-NEXT:    br i1 undef, label [[FOR_COND12_SPLIT:%.*]], label [[EXIT:%.*]]
+; CHECK:       for.cond12.split:
+; CHECK-NEXT:    call void @callee(i16 [[S]])
+; CHECK-NEXT:    br label [[FOR_COND12]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i16 [[ADD2]]
+;
+entry:
+  %s= select i1 undef, i16 1, i16 0
+  %tobool18 = icmp ne i16 %s, 0
+  br i1 %tobool18, label %for.cond12.us, label %for.cond12
+
+for.cond12.us:
+  unreachable
+
+for.cond12:
+  call void @callee(i16 %s)
+  %add = add i16 %s, 10
+  %add2 = add i16 %add, 10
+  br i1 undef, label %for.cond12, label %exit
+
+exit:
+  ret i16 %add2
+}
+
+define internal void @callee(i16 %flag) {
+  ret void
+}