Index: lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -612,9 +612,11 @@
   if (ICmpInst::isSigned(Cond))
     return nullptr;
 
-  // Look through bitcasts.
+  // Look through bitcasts and addrspacecasts.
   if (BitCastInst *BCI = dyn_cast<BitCastInst>(RHS))
     RHS = BCI->getOperand(0);
+  else if (AddrSpaceCastInst *ASCI = dyn_cast<AddrSpaceCastInst>(RHS))
+    RHS = ASCI->getOperand(0);
 
   Value *PtrBase = GEPLHS->getOperand(0);
   if (DL && PtrBase == RHS && GEPLHS->isInBounds()) {
@@ -655,9 +657,24 @@
           (GEPRHS->hasAllConstantIndices() || GEPRHS->hasOneUse()) &&
           PtrBase->stripPointerCasts() ==
             GEPRHS->getOperand(0)->stripPointerCasts()) {
+        Value *LOffset = EmitGEPOffset(GEPLHS);
+        Value *ROffset = EmitGEPOffset(GEPRHS);
+
+        // If we looked through an addrspacecast between different sized address
+        // spaces, the LHS and RHS pointers are different sized
+        // integers. Truncate to the smaller one.
+        Type *LHSIndexTy = LOffset->getType();
+        Type *RHSIndexTy = ROffset->getType();
+        if (LHSIndexTy != RHSIndexTy) {
+          if (LHSIndexTy->getPrimitiveSizeInBits() <
+              RHSIndexTy->getPrimitiveSizeInBits()) {
+            ROffset = Builder->CreateTrunc(ROffset, LHSIndexTy);
+          } else
+            LOffset = Builder->CreateTrunc(LOffset, RHSIndexTy);
+        }
+
         Value *Cmp = Builder->CreateICmp(ICmpInst::getSignedPredicate(Cond),
-                                         EmitGEPOffset(GEPLHS),
-                                         EmitGEPOffset(GEPRHS));
+                                         LOffset, ROffset);
         return ReplaceInstUsesWith(I, Cmp);
       }
 
Index: test/Transforms/InstCombine/icmp.ll
===================================================================
--- test/Transforms/InstCombine/icmp.ll
+++ test/Transforms/InstCombine/icmp.ll
@@ -1,7 +1,6 @@
 ; RUN: opt < %s -instcombine -S | FileCheck %s
 
-target datalayout =
-"e-p:64:64:64-p1:16:16:16-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target datalayout = "e-p:64:64:64-p1:16:16:16-p2:32:32:32-p3:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
 
 define i32 @test1(i32 %X) {
 entry:
@@ -674,6 +673,49 @@
 ; CHECK-NEXT: ret i1
 }
 
+; Same as test60, but look through an addrspacecast instead of a
+; bitcast. This uses the same sized addrspace.
+define i1 @test60_addrspacecast(i8* %foo, i64 %i, i64 %j) {
+  %bit = addrspacecast i8* %foo to i32 addrspace(3)*
+  %gep1 = getelementptr inbounds i32 addrspace(3)* %bit, i64 %i
+  %gep2 = getelementptr inbounds i8* %foo, i64 %j
+  %cast1 = addrspacecast i32 addrspace(3)* %gep1 to i8*
+  %cmp = icmp ult i8* %cast1, %gep2
+  ret i1 %cmp
+; CHECK-LABEL: @test60_addrspacecast(
+; CHECK-NEXT: %gep1.idx = shl nuw i64 %i, 2
+; CHECK-NEXT: icmp slt i64 %gep1.idx, %j
+; CHECK-NEXT: ret i1
+}
+
+define i1 @test60_addrspacecast_smaller(i8* %foo, i16 %i, i64 %j) {
+  %bit = addrspacecast i8* %foo to i32 addrspace(1)*
+  %gep1 = getelementptr inbounds i32 addrspace(1)* %bit, i16 %i
+  %gep2 = getelementptr inbounds i8* %foo, i64 %j
+  %cast1 = addrspacecast i32 addrspace(1)* %gep1 to i8*
+  %cmp = icmp ult i8* %cast1, %gep2
+  ret i1 %cmp
+; CHECK-LABEL: @test60_addrspacecast_smaller(
+; CHECK-NEXT: %gep1.idx = shl nuw i16 %i, 2
+; CHECK-NEXT: trunc i64 %j to i16
+; CHECK-NEXT: icmp sgt i16 %1, %gep1.idx
+; CHECK-NEXT: ret i1
+}
+
+define i1 @test60_addrspacecast_larger(i8 addrspace(1)* %foo, i32 %i, i16 %j) {
+  %bit = addrspacecast i8 addrspace(1)* %foo to i32 addrspace(2)*
+  %gep1 = getelementptr inbounds i32 addrspace(2)* %bit, i32 %i
+  %gep2 = getelementptr inbounds i8 addrspace(1)* %foo, i16 %j
+  %cast1 = addrspacecast i32 addrspace(2)* %gep1 to i8 addrspace(1)*
+  %cmp = icmp ult i8 addrspace(1)* %cast1, %gep2
+  ret i1 %cmp
+; CHECK-LABEL: @test60_addrspacecast_larger(
+; CHECK-NEXT:  %gep1.idx = shl nuw i32 %i, 2
+; CHECK-NEXT:  trunc i32 %gep1.idx to i16
+; CHECK-NEXT:  icmp slt i16 %1, %j
+; CHECK-NEXT:  ret i1
+}
+
 define i1 @test61(i8* %foo, i64 %i, i64 %j) {
   %bit = bitcast i8* %foo to i32*
   %gep1 = getelementptr i32* %bit, i64 %i