Index: llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
===================================================================
--- llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
+++ llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
@@ -736,6 +736,9 @@
       .libcallFor({s128})
       .minScalar(0, MinFPScalar);
 
+  // TODO: Libcall support for s128.
+  getActionDefinitionsBuilder(G_LROUND).legalFor({{s64, s32}, {s64, s64}});
+
   getLegacyLegalizerInfo().computeTables();
   verify(*ST.getInstrInfo());
 }
Index: llvm/test/CodeGen/AArch64/GlobalISel/legalize-lround.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AArch64/GlobalISel/legalize-lround.mir
@@ -0,0 +1,39 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=aarch64 -run-pass=legalizer -verify-machineinstrs %s -o - | FileCheck %s
+
+...
+---
+name:            s64_s32_legal
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $s0
+    ; CHECK-LABEL: name: s64_s32_legal
+    ; CHECK: liveins: $s0
+    ; CHECK: %copy:_(s32) = COPY $s0
+    ; CHECK: %lround:_(s64) = G_LROUND %copy(s32)
+    ; CHECK: %trunc:_(s32) = G_TRUNC %lround(s64)
+    ; CHECK: $w0 = COPY %trunc(s32)
+    ; CHECK: RET_ReallyLR implicit $w0
+    %copy:_(s32) = COPY $s0
+    %lround:_(s64) = G_LROUND %copy(s32)
+    %trunc:_(s32) = G_TRUNC %lround
+    $w0 = COPY %trunc(s32)
+    RET_ReallyLR implicit $w0
+...
+---
+name:            s64_s64_legal
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $d0
+    ; CHECK-LABEL: name: s64_s64_legal
+    ; CHECK: liveins: $d0
+    ; CHECK: %copy:_(s64) = COPY $d0
+    ; CHECK: %lround:_(s64) = G_LROUND %copy(s64)
+    ; CHECK: $x0 = COPY %lround(s64)
+    ; CHECK: RET_ReallyLR implicit $x0
+    %copy:_(s64) = COPY $d0
+    %lround:_(s64) = G_LROUND %copy(s64)
+    $x0 = COPY %lround
+    RET_ReallyLR implicit $x0