diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -580,15 +580,18 @@
     break;
   case TargetOpcode::G_MEMCPY:
     RTLibcall = RTLIB::MEMCPY;
+    Args[0].Flags[0].setReturned();
     break;
   case TargetOpcode::G_MEMMOVE:
     RTLibcall = RTLIB::MEMMOVE;
+    Args[0].Flags[0].setReturned();
     break;
   case TargetOpcode::G_MEMSET:
     RTLibcall = RTLIB::MEMSET;
+    Args[0].Flags[0].setReturned();
     break;
   default:
-    return LegalizerHelper::UnableToLegalize;
+    llvm_unreachable("unsupported opcode");
   }
   const char *Name = TLI.getLibcallName(RTLibcall);
 
@@ -610,7 +613,6 @@
   if (!CLI.lowerCall(MIRBuilder, Info))
     return LegalizerHelper::UnableToLegalize;
 
-
   if (Info.LoweredTailCall) {
     assert(Info.IsTailCall && "Lowered tail call when it wasn't a tail call?");
 
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-memcpy-et-al.mir b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-memcpy-et-al.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-memcpy-et-al.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-memcpy-et-al.mir
@@ -18,7 +18,7 @@
     ; CHECK: $x0 = COPY [[COPY]](p0)
     ; CHECK: $x1 = COPY [[COPY1]](p0)
     ; CHECK: $x2 = COPY [[ZEXT]](s64)
-    ; CHECK: BL &memcpy, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit $x0, implicit $x1, implicit $x2
+    ; CHECK: BL &memcpy, csr_aarch64_aapcs_thisreturn, implicit-def $lr, implicit $sp, implicit $x0, implicit $x1, implicit $x2
     ; CHECK: ADJCALLSTACKUP 0, 0, implicit-def $sp, implicit $sp
     ; CHECK: RET_ReallyLR
     %0:_(p0) = COPY $x0
@@ -71,7 +71,7 @@
     ; CHECK: $x0 = COPY [[COPY]](p0)
     ; CHECK: $x1 = COPY [[COPY1]](p0)
     ; CHECK: $x2 = COPY [[ZEXT]](s64)
-    ; CHECK: BL &memmove, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit $x0, implicit $x1, implicit $x2
+    ; CHECK: BL &memmove, csr_aarch64_aapcs_thisreturn, implicit-def $lr, implicit $sp, implicit $x0, implicit $x1, implicit $x2
     ; CHECK: ADJCALLSTACKUP 0, 0, implicit-def $sp, implicit $sp
     ; CHECK: RET_ReallyLR
     %0:_(p0) = COPY $x0
@@ -100,7 +100,7 @@
     ; CHECK: [[COPY3:%[0-9]+]]:_(s32) = COPY [[COPY1]](s32)
     ; CHECK: $w1 = COPY [[COPY3]](s32)
     ; CHECK: $x2 = COPY [[ZEXT]](s64)
-    ; CHECK: BL &memset, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit $x0, implicit $w1, implicit $x2
+    ; CHECK: BL &memset, csr_aarch64_aapcs_thisreturn, implicit-def $lr, implicit $sp, implicit $x0, implicit $w1, implicit $x2
     ; CHECK: ADJCALLSTACKUP 0, 0, implicit-def $sp, implicit $sp
     ; CHECK: RET_ReallyLR
     %0:_(p0) = COPY $x0
@@ -129,7 +129,7 @@
     ; CHECK: $x0 = COPY [[COPY]](p0)
     ; CHECK: $x1 = COPY [[COPY1]](p0)
     ; CHECK: $x2 = COPY [[ZEXT]](s64)
-    ; CHECK: BL &memcpy, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit $x0, implicit $x1, implicit $x2
+    ; CHECK: BL &memcpy, csr_aarch64_aapcs_thisreturn, implicit-def $lr, implicit $sp, implicit $x0, implicit $x1, implicit $x2
     ; CHECK: ADJCALLSTACKUP 0, 0, implicit-def $sp, implicit $sp
     ; CHECK: $x0 = COPY [[ZEXT]](s64)
     ; CHECK: RET_ReallyLR implicit $x0
@@ -158,7 +158,7 @@
     ; CHECK: $x0 = COPY [[COPY]](p0)
     ; CHECK: $x1 = COPY [[COPY1]](p0)
     ; CHECK: $x2 = COPY [[ZEXT]](s64)
-    ; CHECK: BL &memcpy, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit $x0, implicit $x1, implicit $x2
+    ; CHECK: BL &memcpy, csr_aarch64_aapcs_thisreturn, implicit-def $lr, implicit $sp, implicit $x0, implicit $x1, implicit $x2
     ; CHECK: ADJCALLSTACKUP 0, 0, implicit-def $sp, implicit $sp
     ; CHECK: TCRETURNdi &memset, 0, csr_aarch64_aapcs, implicit $sp
     %0:_(p0) = COPY $x0
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-memlib-debug-loc.mir b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-memlib-debug-loc.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-memlib-debug-loc.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-memlib-debug-loc.mir
@@ -47,7 +47,7 @@
 
     ; We're checking that the BL call has the debug loc of the original intrinsic call.
     ; CHECK-LABEL: name: test_memset_debug
-    ; CHECK: BL &memset, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit $x0, implicit $w1, implicit $x2, debug-location !11
+    ; CHECK: BL &memset, csr_aarch64_aapcs_thisreturn, implicit-def $lr, implicit $sp, implicit $x0, implicit $w1, implicit $x2, debug-location !11
     ; CHECK: RET_ReallyLR debug-location !12
     %0:_(p0) = COPY $x0
     %1:_(s32) = COPY $w1