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
@@ -633,6 +633,21 @@
     MI.eraseFromParent();
     return Legalized;
   }
+  case TargetOpcode::G_TRUNC: {
+    if (TypeIdx != 1)
+      return UnableToLegalize;
+
+    uint64_t SizeOp1 = MRI.getType(MI.getOperand(1).getReg()).getSizeInBits();
+    if (NarrowTy.getSizeInBits() * 2 != SizeOp1) {
+      LLVM_DEBUG(dbgs() << "Can't narrow trunc to type " << NarrowTy << "\n");
+      return UnableToLegalize;
+    }
+
+    auto Unmerge = MIRBuilder.buildUnmerge(NarrowTy, MI.getOperand(1).getReg());
+    MIRBuilder.buildCopy(MI.getOperand(0).getReg(), Unmerge.getReg(0));
+    MI.eraseFromParent();
+    return Legalized;
+  }
 
   case TargetOpcode::G_ADD: {
     // FIXME: add support for when SizeOp0 isn't an exact multiple of
diff --git a/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp b/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp
--- a/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp
@@ -54,6 +54,10 @@
                                {s32, p0, 16, 8}})
       .minScalar(0, s32);
 
+  getActionDefinitionsBuilder(G_TRUNC)
+      .legalIf([](const LegalityQuery &Query) { return false; })
+      .maxScalar(1, s32);
+
   getActionDefinitionsBuilder(G_SELECT)
       .legalForCartesianProduct({p0, s32, s64}, {s32})
       .minScalar(0, s32)
diff --git a/llvm/test/CodeGen/Mips/GlobalISel/legalizer/trunc.mir b/llvm/test/CodeGen/Mips/GlobalISel/legalizer/trunc.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/Mips/GlobalISel/legalizer/trunc.mir
@@ -0,0 +1,30 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -O0 -mtriple=mipsel-linux-gnu -run-pass=legalizer -verify-machineinstrs %s -o - | FileCheck %s -check-prefixes=MIPS32
+--- |
+
+  define void @trunc() {entry: ret void}
+
+...
+---
+name:            trunc
+alignment:       2
+tracksRegLiveness: true
+body:             |
+  bb.1.entry:
+    liveins: $a0, $a1
+
+    ; MIPS32-LABEL: name: trunc
+    ; MIPS32: liveins: $a0, $a1
+    ; MIPS32: [[COPY:%[0-9]+]]:_(s32) = COPY $a0
+    ; MIPS32: [[COPY1:%[0-9]+]]:_(s32) = COPY $a1
+    ; MIPS32: [[COPY2:%[0-9]+]]:_(s32) = COPY [[COPY]](s32)
+    ; MIPS32: $v0 = COPY [[COPY2]](s32)
+    ; MIPS32: RetRA implicit $v0
+    %1:_(s32) = COPY $a0
+    %2:_(s32) = COPY $a1
+    %0:_(s64) = G_MERGE_VALUES %1(s32), %2(s32)
+    %3:_(s32) = G_TRUNC %0(s64)
+    $v0 = COPY %3(s32)
+    RetRA implicit $v0
+
+...
diff --git a/llvm/test/CodeGen/Mips/GlobalISel/llvm-ir/trunc.ll b/llvm/test/CodeGen/Mips/GlobalISel/llvm-ir/trunc.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/Mips/GlobalISel/llvm-ir/trunc.ll
@@ -0,0 +1,13 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc  -O0 -mtriple=mipsel-linux-gnu -global-isel  -verify-machineinstrs %s -o -| FileCheck %s -check-prefixes=MIPS32
+
+define i32 @trunc(i64 %x) {
+; MIPS32-LABEL: trunc:
+; MIPS32:       # %bb.0: # %entry
+; MIPS32-NEXT:    move $2, $4
+; MIPS32-NEXT:    jr $ra
+; MIPS32-NEXT:    nop
+entry:
+  %conv = trunc i64 %x to i32
+  ret i32 %conv
+}