Index: lib/Transforms/Scalar/CallSiteSplitting.cpp
===================================================================
--- lib/Transforms/Scalar/CallSiteSplitting.cpp
+++ lib/Transforms/Scalar/CallSiteSplitting.cpp
@@ -183,6 +183,9 @@
 }
 
 static bool canSplitCallSite(CallSite CS, TargetTransformInfo &TTI) {
+  if (CS.isConvergent() || CS.cannotDuplicate())
+    return false;
+
   // FIXME: As of now we handle only CallInst. InvokeInst could be handled
   // without too much effort.
   Instruction *Instr = CS.getInstruction();
Index: test/Transforms/CallSiteSplitting/convergent.ll
===================================================================
--- /dev/null
+++ test/Transforms/CallSiteSplitting/convergent.ll
@@ -0,0 +1,197 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -callsite-splitting -callsite-splitting-duplication-threshold=100000000  < %s | FileCheck --check-prefix=CHECK %s
+
+; Convergent calls should not be duplicated in this case
+define void @convergent_caller(i1 %c, i8* %a_elt, i8* %b_elt) #0 {
+; CHECK-LABEL: @convergent_caller(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[TOP:%.*]]
+; CHECK:       Top:
+; CHECK-NEXT:    [[TOBOOL1:%.*]] = icmp eq i8* [[A_ELT:%.*]], null
+; CHECK-NEXT:    br i1 [[TOBOOL1]], label [[CALLSITEBB:%.*]], label [[NEXTCOND:%.*]]
+; CHECK:       NextCond:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8* [[B_ELT:%.*]], null
+; CHECK-NEXT:    br i1 [[CMP]], label [[CALLSITEBB]], label [[END:%.*]]
+; CHECK:       CallSiteBB:
+; CHECK-NEXT:    [[P:%.*]] = phi i1 [ false, [[TOP]] ], [ [[C:%.*]], [[NEXTCOND]] ]
+; CHECK-NEXT:    call void @convergent_callee(i8* [[A_ELT]], i1 [[P]])
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       End:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %Top
+
+Top:
+  %tobool1 = icmp eq i8* %a_elt, null
+  br i1 %tobool1, label %CallSiteBB, label %NextCond
+
+NextCond:
+  %cmp = icmp ne i8* %b_elt, null
+  br i1 %cmp, label %CallSiteBB, label %End
+
+CallSiteBB:
+  %p = phi i1 [ false, %Top ], [ %c, %NextCond ]
+  call void @convergent_callee(i8* %a_elt, i1 %p)
+  br label %End
+
+End:
+  ret void
+}
+
+define void @convergent_callee(i8* %a_elt, i1 %c) #0 {
+; CHECK-LABEL: @convergent_callee(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8* [[A_ELT:%.*]], null
+; CHECK-NEXT:    br i1 [[TOBOOL]], label [[THEN:%.*]], label [[ENDIF:%.*]]
+; CHECK:       then:
+; CHECK-NEXT:    br label [[ENDIF]]
+; CHECK:       endif:
+; CHECK-NEXT:    call void @convergent_external(i8* [[A_ELT]]) #0
+; CHECK-NEXT:    ret void
+;
+entry:
+  %tobool = icmp ne i8* %a_elt, null
+  br i1 %tobool, label %then, label %endif
+
+then:
+  br label %endif
+
+endif:
+  call void @convergent_external(i8* %a_elt) #0
+  ret void
+}
+
+; Noduplicate calls should not be duplicated
+define void @noduplicate_caller(i1 %c, i8* %a_elt, i8* %b_elt) #2 {
+; CHECK-LABEL: @noduplicate_caller(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[TOP:%.*]]
+; CHECK:       Top:
+; CHECK-NEXT:    [[TOBOOL1:%.*]] = icmp eq i8* [[A_ELT:%.*]], null
+; CHECK-NEXT:    br i1 [[TOBOOL1]], label [[CALLSITEBB:%.*]], label [[NEXTCOND:%.*]]
+; CHECK:       NextCond:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8* [[B_ELT:%.*]], null
+; CHECK-NEXT:    br i1 [[CMP]], label [[CALLSITEBB]], label [[END:%.*]]
+; CHECK:       CallSiteBB:
+; CHECK-NEXT:    [[P:%.*]] = phi i1 [ false, [[TOP]] ], [ [[C:%.*]], [[NEXTCOND]] ]
+; CHECK-NEXT:    call void @noduplicate_callee(i8* [[A_ELT]], i1 [[P]])
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       End:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %Top
+
+Top:
+  %tobool1 = icmp eq i8* %a_elt, null
+  br i1 %tobool1, label %CallSiteBB, label %NextCond
+
+NextCond:
+  %cmp = icmp ne i8* %b_elt, null
+  br i1 %cmp, label %CallSiteBB, label %End
+
+CallSiteBB:
+  %p = phi i1 [ false, %Top ], [ %c, %NextCond ]
+  call void @noduplicate_callee(i8* %a_elt, i1 %p)
+  br label %End
+
+End:
+  ret void
+}
+
+define void @noduplicate_callee(i8* %a_elt, i1 %c) #2 {
+; CHECK-LABEL: @noduplicate_callee(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8* [[A_ELT:%.*]], null
+; CHECK-NEXT:    br i1 [[TOBOOL]], label [[THEN:%.*]], label [[ENDIF:%.*]]
+; CHECK:       then:
+; CHECK-NEXT:    br label [[ENDIF]]
+; CHECK:       endif:
+; CHECK-NEXT:    call void @noduplicate_external(i8* [[A_ELT]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  %tobool = icmp ne i8* %a_elt, null
+  br i1 %tobool, label %then, label %endif
+
+then:
+  br label %endif
+
+endif:
+  call void @noduplicate_external(i8* %a_elt)
+  ret void
+}
+
+; Make sure an otherwise identical function is transformed
+define void @reference_caller(i1 %c, i8* %a_elt, i8* %b_elt) #1 {
+; CHECK-LABEL: @reference_caller(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[TOP:%.*]]
+; CHECK:       Top:
+; CHECK-NEXT:    [[TOBOOL1:%.*]] = icmp eq i8* [[A_ELT:%.*]], null
+; CHECK-NEXT:    br i1 [[TOBOOL1]], label [[TOP_SPLIT:%.*]], label [[NEXTCOND:%.*]]
+; CHECK:       Top.split:
+; CHECK-NEXT:    call void @nonconvergent_callee(i8* null, i1 false)
+; CHECK-NEXT:    br label [[CALLSITEBB:%.*]]
+; CHECK:       NextCond:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8* [[B_ELT:%.*]], null
+; CHECK-NEXT:    br i1 [[CMP]], label [[NEXTCOND_SPLIT:%.*]], label [[END:%.*]]
+; CHECK:       NextCond.split:
+; CHECK-NEXT:    call void @nonconvergent_callee(i8* nonnull [[A_ELT]], i1 [[C:%.*]])
+; CHECK-NEXT:    br label [[CALLSITEBB]]
+; CHECK:       CallSiteBB:
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       End:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %Top
+
+Top:
+  %tobool1 = icmp eq i8* %a_elt, null
+  br i1 %tobool1, label %CallSiteBB, label %NextCond
+
+NextCond:
+  %cmp = icmp ne i8* %b_elt, null
+  br i1 %cmp, label %CallSiteBB, label %End
+
+CallSiteBB:
+  %p = phi i1 [ false, %Top ], [ %c, %NextCond ]
+  call void @nonconvergent_callee(i8* %a_elt, i1 %p)
+  br label %End
+
+End:
+  ret void
+}
+
+define void @nonconvergent_callee(i8* %a_elt, i1 %c) #1 {
+; CHECK-LABEL: @nonconvergent_callee(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8* [[A_ELT:%.*]], null
+; CHECK-NEXT:    br i1 [[TOBOOL]], label [[THEN:%.*]], label [[ENDIF:%.*]]
+; CHECK:       then:
+; CHECK-NEXT:    br label [[ENDIF]]
+; CHECK:       endif:
+; CHECK-NEXT:    call void @nonconvergent_external(i8* [[A_ELT]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  %tobool = icmp ne i8* %a_elt, null
+  br i1 %tobool, label %then, label %endif
+
+then:
+  br label %endif
+
+endif:
+  call void @nonconvergent_external(i8* %a_elt)
+  ret void
+}
+
+declare void @convergent_external(i8*) #0
+declare void @nonconvergent_external(i8*) #1
+declare void @noduplicate_external(i8*) #2
+
+attributes #0 = { convergent nounwind }
+attributes #1 = { nounwind }
+attributes #2 = { noduplicate nounwind }