Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1433,6 +1433,29 @@
       return EraseInstFromFunction(CI);
     break;
   }
+  case Intrinsic::lifetime_start: {
+    // Remove trivially empty lifetime_start/end ranges, i.e. a start
+    // immediately followed by an end (ignoring debuginfo or other
+    // lifetime markers in between).
+    BasicBlock::iterator BI = II, BE = II->getParent()->end();
+    for (++BI; BI != BE; ++BI) {
+      if (IntrinsicInst *LTE = dyn_cast<IntrinsicInst>(BI)) {
+        if (isa<DbgInfoIntrinsic>(LTE) ||
+            LTE->getIntrinsicID() == Intrinsic::lifetime_start)
+          continue;
+        if (LTE->getIntrinsicID() == Intrinsic::lifetime_end) {
+          if (II->getOperand(0) == LTE->getOperand(0) &&
+              II->getOperand(1) == LTE->getOperand(1)) {
+            EraseInstFromFunction(*LTE);
+            return EraseInstFromFunction(*II);
+          }
+          continue;
+        }
+      }
+      break;
+    }
+    break;
+  }
   case Intrinsic::assume: {
     // Canonicalize assume(a && b) -> assume(a); assume(b);
     // Note: New assumption intrinsics created here are registered by
Index: llvm/trunk/test/Transforms/InstCombine/lifetime.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/lifetime.ll
+++ llvm/trunk/test/Transforms/InstCombine/lifetime.ll
@@ -0,0 +1,93 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+declare void @llvm.lifetime.start(i64, i8* nocapture)
+declare void @llvm.lifetime.end(i64, i8* nocapture)
+declare void @foo(i8* nocapture, i8* nocapture)
+
+define void @bar(i1 %flag) {
+entry:
+; CHECK-LABEL: @bar(
+; CHECK: %[[T:[^ ]+]] = getelementptr inbounds [1 x i8], [1 x i8]* %text
+; CHECK: %[[B:[^ ]+]] = getelementptr inbounds [1 x i8], [1 x i8]* %buff
+; CHECK: if:
+; CHECK-NEXT: br label %bb2
+; CHECK: bb2:
+; CHECK-NEXT: br label %bb3
+; CHECK: bb3:
+; CHECK-NEXT: call void @llvm.dbg.declare
+; CHECK-NEXT: br label %fin
+; CHECK: call void @llvm.lifetime.start(i64 1, i8* %[[T]])
+; CHECK-NEXT: call void @llvm.lifetime.start(i64 1, i8* %[[B]])
+; CHECK-NEXT: call void @foo(i8* %[[B]], i8* %[[T]])
+; CHECK-NEXT: call void @llvm.lifetime.end(i64 1, i8* %[[B]])
+; CHECK-NEXT: call void @llvm.lifetime.end(i64 1, i8* %[[T]])
+  %text = alloca [1 x i8], align 1
+  %buff = alloca [1 x i8], align 1
+  %0 = getelementptr inbounds [1 x i8], [1 x i8]* %text, i64 0, i64 0
+  %1 = getelementptr inbounds [1 x i8], [1 x i8]* %buff, i64 0, i64 0
+  br i1 %flag, label %if, label %else
+
+if:
+  call void @llvm.lifetime.start(i64 1, i8* %0)
+  call void @llvm.lifetime.start(i64 1, i8* %1)
+  call void @llvm.lifetime.end(i64 1, i8* %1)
+  call void @llvm.lifetime.end(i64 1, i8* %0)
+  br label %bb2
+
+bb2:
+  call void @llvm.lifetime.start(i64 1, i8* %0)
+  call void @llvm.lifetime.start(i64 1, i8* %1)
+  call void @llvm.lifetime.end(i64 1, i8* %0)
+  call void @llvm.lifetime.end(i64 1, i8* %1)
+  br label %bb3
+
+bb3:
+  call void @llvm.lifetime.start(i64 1, i8* %0)
+  call void @llvm.dbg.declare(metadata [1 x i8]* %text, metadata !14, metadata !25), !dbg !26
+  call void @llvm.lifetime.end(i64 1, i8* %0)
+  br label %fin
+
+else:
+  call void @llvm.lifetime.start(i64 1, i8* %0)
+  call void @llvm.lifetime.start(i64 1, i8* %1)
+  call void @foo(i8* %1, i8* %0)
+  call void @llvm.lifetime.end(i64 1, i8* %1)
+  call void @llvm.lifetime.end(i64 1, i8* %0)
+  br  label %fin
+
+fin:
+  ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!22, !23}
+!llvm.ident = !{!24}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.8.0 (trunk 248826) (llvm/trunk 248827)", isOptimized: true, runtimeVersion: 0, emissionKind: 1, enums: !2, subprograms: !3)
+!1 = !DIFile(filename: "test.cpp", directory: "/home/user")
+!2 = !{}
+!3 = !{!4}
+!4 = distinct !DISubprogram(name: "bar", linkageName: "bar", scope: !1, file: !1, line: 2, type: !5, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true, function: void (i1)* @bar, variables: !8)
+!5 = !DISubroutineType(types: !6)
+!6 = !{null, !7}
+!7 = !DIBasicType(name: "bool", size: 8, align: 8, encoding: DW_ATE_boolean)
+!8 = !{!9, !11, !12, !14, !21}
+!9 = !DILocalVariable(name: "Size", arg: 1, scope: !4, file: !1, line: 2, type: !10)
+!10 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!11 = !DILocalVariable(name: "flag", arg: 2, scope: !4, file: !1, line: 2, type: !7)
+!12 = !DILocalVariable(name: "i", scope: !13, file: !1, line: 3, type: !10)
+!13 = distinct !DILexicalBlock(scope: !4, file: !1, line: 3, column: 3)
+!14 = !DILocalVariable(name: "text", scope: !15, file: !1, line: 4, type: !17)
+!15 = distinct !DILexicalBlock(scope: !16, file: !1, line: 3, column: 30)
+!16 = distinct !DILexicalBlock(scope: !13, file: !1, line: 3, column: 3)
+!17 = !DICompositeType(tag: DW_TAG_array_type, baseType: !18, size: 8, align: 8, elements: !19)
+!18 = !DIBasicType(name: "char", size: 8, align: 8, encoding: DW_ATE_signed_char)
+!19 = !{!20}
+!20 = !DISubrange(count: 1)
+!21 = !DILocalVariable(name: "buff", scope: !15, file: !1, line: 5, type: !17)
+!22 = !{i32 2, !"Dwarf Version", i32 4}
+!23 = !{i32 2, !"Debug Info Version", i32 3}
+!24 = !{!"clang version 3.8.0 (trunk 248826) (llvm/trunk 248827)"}
+!25 = !DIExpression()
+!26 = !DILocation(line: 4, column: 10, scope: !15)