Index: lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -120,6 +120,15 @@
     return MI;
   }
 
+  // If we have a store to a location which is known constant, we can conclude
+  // that the store must be storing the constant value (else the memory
+  // wouldn't be constant), and this must be a noop.
+  if (AA->pointsToConstantMemory(MI->getDest())) {
+    // Set the size of the copy to 0, it will be deleted on the next iteration.
+    MI->setLength(Constant::getNullValue(MI->getLength()->getType()));
+    return MI;
+  }
+
   // If MemCpyInst length is 1/2/4/8 bytes then replace memcpy with
   // load/store.
   ConstantInt *MemOpLength = dyn_cast<ConstantInt>(MI->getLength());
@@ -218,6 +227,15 @@
     return MI;
   }
 
+  // If we have a store to a location which is known constant, we can conclude
+  // that the store must be storing the constant value (else the memory
+  // wouldn't be constant), and this must be a noop.
+  if (AA->pointsToConstantMemory(MI->getDest())) {
+    // Set the size of the copy to 0, it will be deleted on the next iteration.
+    MI->setLength(Constant::getNullValue(MI->getLength()->getType()));
+    return MI;
+  }
+
   // Extract the length and alignment and fill if they are constant.
   ConstantInt *LenC = dyn_cast<ConstantInt>(MI->getLength());
   ConstantInt *FillC = dyn_cast<ConstantInt>(MI->getValue());
Index: lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1438,6 +1438,12 @@
     }
   }
 
+  // If we have a store to a location which is known constant, we can conclude
+  // that the store must be storing the constant value (else the memory
+  // wouldn't be constant), and this must be a noop.
+  if (AA->pointsToConstantMemory(Ptr))
+    return eraseInstFromFunction(SI);
+
   // Do really simple DSE, to catch cases where there are several consecutive
   // stores to the same location, separated by a few arithmetic operations. This
   // situation often occurs with bitfield accesses.
Index: test/Transforms/InstCombine/gep-custom-dl.ll
===================================================================
--- test/Transforms/InstCombine/gep-custom-dl.ll
+++ test/Transforms/InstCombine/gep-custom-dl.ll
@@ -8,8 +8,7 @@
 %struct.C = type { [7 x i8] }
 
 
-@Global = constant [10 x i8] c"helloworld"
-
+@Global = external global [10 x i8]
 
 ; Test that two array indexing geps fold
 define i32* @test1(i32* %I) {
Index: test/Transforms/InstCombine/getelementptr.ll
===================================================================
--- test/Transforms/InstCombine/getelementptr.ll
+++ test/Transforms/InstCombine/getelementptr.ll
@@ -9,8 +9,8 @@
 %struct.C = type { [7 x i8] }
 
 
-@Global = constant [10 x i8] c"helloworld"
-@Global_as1 = addrspace(1) constant [10 x i8] c"helloworld"
+@Global = external global [10 x i8]
+@Global_as1 = external addrspace(1) global [10 x i8]
 
 ; Test noop elimination
 define i32* @test1(i32* %I) {
Index: test/Transforms/InstCombine/memcpy.ll
===================================================================
--- test/Transforms/InstCombine/memcpy.ll
+++ test/Transforms/InstCombine/memcpy.ll
@@ -35,3 +35,9 @@
   ret void
 }
 
+@UnknownConstant = external constant i8
+
+define void @memmove_to_constant(i8* %src) {
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* @UnknownConstant, i8* %src, i32 1, i1 false)
+  ret void
+}
Index: test/Transforms/InstCombine/memmove.ll
===================================================================
--- test/Transforms/InstCombine/memmove.ll
+++ test/Transforms/InstCombine/memmove.ll
@@ -1,3 +1,4 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; This test makes sure that memmove instructions are properly eliminated.
 ;
 ; RUN: opt < %s -instcombine -S | FileCheck %s
@@ -8,30 +9,33 @@
 @hello_u = constant [8 x i8] c"hello_u\00"		; <[8 x i8]*> [#uses=1]
 
 define void @test1(i8* %A, i8* %B, i32 %N) {
-  ;; CHECK-LABEL: test1
-  ;; CHECK-NEXT: ret void
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:    ret void
+;
   call void @llvm.memmove.p0i8.p0i8.i32(i8* %A, i8* %B, i32 0, i1 false)
   ret void
 }
 
 define void @test2(i8* %A, i32 %N) {
   ;; dest can't alias source since we can't write to source!
-  ;; CHECK-LABEL: test2
-  ;; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 1 %A, i8* align 16 getelementptr inbounds ([33 x i8], [33 x i8]* @S, i{{32|64}} 0, i{{32|64}} 0), i32 %N, i1 false)
-  ;; CHECK-NEXT: ret void
+; CHECK-LABEL: @test2(
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 1 [[A:%.*]], i8* align 16 getelementptr inbounds ([33 x i8], [33 x i8]* @S, i64 0, i64 0), i32 [[N:%.*]], i1 false)
+; CHECK-NEXT:    ret void
+;
   call void @llvm.memmove.p0i8.p0i8.i32(i8* %A, i8* getelementptr inbounds ([33 x i8], [33 x i8]* @S, i32 0, i32 0), i32 %N, i1 false)
   ret void
 }
 
 define i32 @test3([1024 x i8]* %target) { ; arg: [1024 x i8]*> [#uses=1]
-  ;; CHECK-LABEL: test3
-  ;; CHECK-NEXT: [[P1:%[^\s]+]] = bitcast [1024 x i8]* %target to i16*
-  ;; CHECK-NEXT: store i16 104, i16* [[P1]], align 2
-  ;; CHECK-NEXT: [[P2:%[^\s]+]] = bitcast [1024 x i8]* %target to i32*
-  ;; CHECK-NEXT: store i32 7103848, i32* [[P2]], align 4
-  ;; CHECK-NEXT: [[P3:%[^\s]+]] = bitcast [1024 x i8]* %target to i64*
-  ;; CHECK-NEXT: store i64 33037504440198504, i64* [[P3]], align 8
-  ;; CHECK-NEXT: ret i32 0
+; CHECK-LABEL: @test3(
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast [1024 x i8]* [[TARGET:%.*]] to i16*
+; CHECK-NEXT:    store i16 104, i16* [[TMP1]], align 2
+; CHECK-NEXT:    [[TMP2:%.*]] = bitcast [1024 x i8]* [[TARGET]] to i32*
+; CHECK-NEXT:    store i32 7103848, i32* [[TMP2]], align 4
+; CHECK-NEXT:    [[TMP3:%.*]] = bitcast [1024 x i8]* [[TARGET]] to i64*
+; CHECK-NEXT:    store i64 33037504440198504, i64* [[TMP3]], align 8
+; CHECK-NEXT:    ret i32 0
+;
   %h_p = getelementptr [2 x i8], [2 x i8]* @h, i32 0, i32 0		; <i8*> [#uses=1]
   %hel_p = getelementptr [4 x i8], [4 x i8]* @hel, i32 0, i32 0		; <i8*> [#uses=1]
   %hello_u_p = getelementptr [8 x i8], [8 x i8]* @hello_u, i32 0, i32 0		; <i8*> [#uses=1]
@@ -44,10 +48,22 @@
 
 ; PR2370
 define void @test4(i8* %a) {
-  ;; CHECK-LABEL: test4
-  ;; CHECK-NEXT: ret void
+; CHECK-LABEL: @test4(
+; CHECK-NEXT:    ret void
+;
   tail call void @llvm.memmove.p0i8.p0i8.i32(i8* %a, i8* %a, i32 100, i1 false)
   ret void
 }
 
+@UnknownConstant = external constant i8
+
+define void @memmove_to_constant(i8* %src) {
+; CHECK-LABEL: @memmove_to_constant(
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0i8.p0i8.i32(i8* @UnknownConstant, i8* %src, i32 1, i1 false)
+  ret void
+}
+
+
 declare void @llvm.memmove.p0i8.p0i8.i32(i8* nocapture, i8* nocapture readonly, i32, i1) argmemonly nounwind
Index: test/Transforms/InstCombine/memset.ll
===================================================================
--- test/Transforms/InstCombine/memset.ll
+++ test/Transforms/InstCombine/memset.ll
@@ -1,16 +1,18 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -instcombine -S | FileCheck %s
 
 define i32 @test([1024 x i8]* %target) {
-  ;; CHECK-LABEL: test
-  ;; CHECK-NEXT: [[P1:%[^\s]+]] = getelementptr inbounds [1024 x i8], [1024 x i8]* %target, i64 0, i64 0
-  ;; CHECK-NEXT: store i8 1, i8* [[P1]], align 1
-  ;; CHECK-NEXT: [[P2:%[^\s]+]] = bitcast [1024 x i8]* %target to i16*
-  ;; CHECK-NEXT: store i16 257, i16* [[P2]], align 2
-  ;; CHECK-NEXT: [[P3:%[^\s]+]] = bitcast [1024 x i8]* %target to i32*
-  ;; CHECK-NEXT: store i32 16843009, i32* [[P3]], align 4
-  ;; CHECK-NEXT: [[P4:%[^\s]+]] = bitcast [1024 x i8]* %target to i64*
-  ;; CHECK-NEXT: store i64 72340172838076673, i64* [[P4]], align 8
-  ;; CHECK-NEXT: ret i32 0
+; CHECK-LABEL: @test(
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds [1024 x i8], [1024 x i8]* [[TARGET:%.*]], i64 0, i64 0
+; CHECK-NEXT:    store i8 1, i8* [[TMP1]], align 1
+; CHECK-NEXT:    [[TMP2:%.*]] = bitcast [1024 x i8]* [[TARGET]] to i16*
+; CHECK-NEXT:    store i16 257, i16* [[TMP2]], align 2
+; CHECK-NEXT:    [[TMP3:%.*]] = bitcast [1024 x i8]* [[TARGET]] to i32*
+; CHECK-NEXT:    store i32 16843009, i32* [[TMP3]], align 4
+; CHECK-NEXT:    [[TMP4:%.*]] = bitcast [1024 x i8]* [[TARGET]] to i64*
+; CHECK-NEXT:    store i64 72340172838076673, i64* [[TMP4]], align 8
+; CHECK-NEXT:    ret i32 0
+;
   %target_p = getelementptr [1024 x i8], [1024 x i8]* %target, i32 0, i32 0
   call void @llvm.memset.p0i8.i32(i8* %target_p, i8 1, i32 0, i1 false)
   call void @llvm.memset.p0i8.i32(i8* %target_p, i8 1, i32 1, i1 false)
@@ -20,4 +22,15 @@
   ret i32 0
 }
 
+@Unknown = external constant i32
+
+define void @memset_to_constant() {
+; CHECK-LABEL: @memset_to_constant(
+; CHECK-NEXT:    ret void
+;
+  %p = bitcast i32* @Unknown to i8*
+  call void @llvm.memset.p0i8.i32(i8* %p, i8 0, i32 5, i1 false)
+  ret void
+}
+
 declare void @llvm.memset.p0i8.i32(i8* nocapture writeonly, i8, i32, i1) argmemonly nounwind
Index: test/Transforms/InstCombine/store.ll
===================================================================
--- test/Transforms/InstCombine/store.ll
+++ test/Transforms/InstCombine/store.ll
@@ -291,6 +291,16 @@
   ret void
 }
 
+@Unknown = external constant i32
+
+define void @store_to_constant() {
+; CHECK-LABEL: @store_to_constant(
+; CHECK-NEXT:    ret void
+;
+  store i32 0, i32* @Unknown
+  ret void
+}
+
 !0 = !{!4, !4, i64 0}
 !1 = !{!"omnipotent char", !2}
 !2 = !{!"Simple C/C++ TBAA"}