Index: include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
+++ include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
@@ -39,6 +39,7 @@
 class MachineIRBuilder;
 class MachineRegisterInfo;
 class MCInstrInfo;
+class TargetLowering;
 
 namespace LegalizeActions {
 enum LegalizeAction : std::uint8_t {
@@ -205,6 +206,9 @@
 /// True iff the specified type index is a vector whose element count is not a
 /// power of 2.
 LegalityPredicate numElementsNotPow2(unsigned TypeIdx);
+/// True iff the pointer addressspacecast b/w Types at indices 0 and 1 are a
+/// noop.
+LegalityPredicate isNoopAddrSpaceCast(const TargetLowering *TLI);
 } // end namespace LegalityPredicates
 
 namespace LegalizeMutations {
@@ -696,6 +700,13 @@
         .clampMaxNumElements(TypeIdx, EltTy, MaxTy.getNumElements());
   }
 
+  /// Legal if the address space cast b/w the two pointers is a noop.
+  LegalizeRuleSet &legalIfNoopAddrSpaceCast(const TargetLowering *TLI) {
+    markAllTypeIdxsAsCovered();
+    return actionIf(LegalizeAction::Legal,
+                    LegalityPredicates::isNoopAddrSpaceCast(TLI));
+  }
+
   /// Fallback on the previous implementation. This should only be used while
   /// porting a rule.
   LegalizeRuleSet &fallback() {
Index: lib/CodeGen/GlobalISel/LegalityPredicates.cpp
===================================================================
--- lib/CodeGen/GlobalISel/LegalityPredicates.cpp
+++ lib/CodeGen/GlobalISel/LegalityPredicates.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
+#include "llvm/CodeGen/TargetLowering.h"
 
 using namespace llvm;
 
@@ -94,3 +95,14 @@
     return QueryTy.isVector() && isPowerOf2_32(QueryTy.getNumElements());
   };
 }
+
+LegalityPredicate
+LegalityPredicates::isNoopAddrSpaceCast(const TargetLowering *TLI) {
+  return [=](const LegalityQuery &Query) {
+    const LLT &Ty0 = Query.Types[0];
+    const LLT &Ty1 = Query.Types[1];
+    assert(Ty0.isPointer() && Ty1.isPointer());
+    return TLI->isNoopAddrSpaceCast(Ty1.getAddressSpace(),
+                                    Ty0.getAddressSpace());
+  };
+}
Index: lib/Target/AArch64/AArch64LegalizerInfo.cpp
===================================================================
--- lib/Target/AArch64/AArch64LegalizerInfo.cpp
+++ lib/Target/AArch64/AArch64LegalizerInfo.cpp
@@ -52,6 +52,9 @@
       .clampScalar(0, s1, s64)
       .widenScalarToNextPow2(0, 8);
 
+  getActionDefinitionsBuilder(G_ADDRSPACE_CAST)
+      .legalIfNoopAddrSpaceCast(ST.getTargetLowering());
+
   getActionDefinitionsBuilder(G_PHI)
       .legalFor({p0, s16, s32, s64})
       .clampScalar(0, s16, s64)
Index: test/CodeGen/AArch64/GlobalISel/legalize-addrspacecast.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/GlobalISel/legalize-addrspacecast.mir
@@ -0,0 +1,21 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -o - -mtriple=aarch64-- -global-isel -run-pass=legalizer %s | FileCheck %s
+
+---
+name:            test_addrspacecast
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_addrspacecast
+    ; CHECK: [[DEF:%[0-9]+]]:_(s64) = G_IMPLICIT_DEF
+    ; CHECK: [[INTTOPTR:%[0-9]+]]:_(p0) = G_INTTOPTR [[DEF]](s64)
+    ; CHECK: [[ADDRSPACE_CAST:%[0-9]+]]:_(p1) = G_ADDRSPACE_CAST [[INTTOPTR]](p0)
+    ; CHECK: [[ADDRSPACE_CAST1:%[0-9]+]]:_(p0) = G_ADDRSPACE_CAST [[ADDRSPACE_CAST]](p1)
+    ; CHECK: [[PTRTOINT:%[0-9]+]]:_(s64) = G_PTRTOINT [[ADDRSPACE_CAST1]](p0)
+    ; CHECK: $x0 = COPY [[PTRTOINT]](s64)
+    %0:_(s64) = G_IMPLICIT_DEF
+    %1:_(p0) = G_INTTOPTR %0
+    %2:_(p1) = G_ADDRSPACE_CAST %1
+    %3:_(p0) = G_ADDRSPACE_CAST %2
+    %4:_(s64) = G_PTRTOINT %3
+    $x0 = COPY %4
+...