diff --git a/llvm/lib/Target/X86/X86LegalizerInfo.cpp b/llvm/lib/Target/X86/X86LegalizerInfo.cpp
--- a/llvm/lib/Target/X86/X86LegalizerInfo.cpp
+++ b/llvm/lib/Target/X86/X86LegalizerInfo.cpp
@@ -99,6 +99,11 @@
 
 
   if (Subtarget.is64Bit()) {
+    getActionDefinitionsBuilder(G_BSWAP)
+      .legalFor({s32, s64})
+      .widenScalarToNextPow2(0, /*Min=*/32)
+      .clampScalar(0, s32, s64);
+
     if (Subtarget.hasPOPCNT()) {
       // popcount
       getActionDefinitionsBuilder(G_CTPOP)
@@ -115,6 +120,14 @@
         .clampScalar(1, s16, s64);
     }
   } else { // 32-bit
+    getActionDefinitionsBuilder(G_BSWAP)
+      .legalIf([=](const LegalityQuery &Query) {
+        // workaround for legalFor
+        return Query.Types[0] == s32;
+      })
+      .widenScalarToNextPow2(0, /*Min=*/32)
+      .clampScalar(0, s32, s32);
+
     if (Subtarget.hasPOPCNT()) {
       // popcount
       getActionDefinitionsBuilder(G_CTPOP)
diff --git a/llvm/test/CodeGen/X86/GlobalISel/legalize-bswap.mir b/llvm/test/CodeGen/X86/GlobalISel/legalize-bswap.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/X86/GlobalISel/legalize-bswap.mir
@@ -0,0 +1,76 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 2
+# RUN: llc -mtriple=x86_64-linux-gnu -run-pass=legalizer %s -o - | FileCheck %s --check-prefix=X86-64
+# RUN: llc -mtriple=i386-linux-gnu -run-pass=legalizer %s -o - | FileCheck %s --check-prefix=X86-32
+
+# test BSWAP s32 and s64
+
+...
+---
+name:            test_bswaps64
+body:             |
+  bb.1:
+    ; X86-64-LABEL: name: test_bswaps64
+    ; X86-64: [[DEF:%[0-9]+]]:_(s64) = IMPLICIT_DEF
+    ; X86-64-NEXT: [[BSWAP:%[0-9]+]]:_(s64) = G_BSWAP [[DEF]]
+    ; X86-64-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY [[BSWAP]](s64)
+    ; X86-64-NEXT: RET 0, implicit [[COPY]](s64)
+    ; X86-32-LABEL: name: test_bswaps64
+    ; X86-32: [[DEF:%[0-9]+]]:_(s64) = IMPLICIT_DEF
+    ; X86-32-NEXT: [[UV:%[0-9]+]]:_(s32), [[UV1:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[DEF]](s64)
+    ; X86-32-NEXT: [[BSWAP:%[0-9]+]]:_(s32) = G_BSWAP [[UV1]]
+    ; X86-32-NEXT: [[BSWAP1:%[0-9]+]]:_(s32) = G_BSWAP [[UV]]
+    ; X86-32-NEXT: [[MV:%[0-9]+]]:_(s64) = G_MERGE_VALUES [[BSWAP]](s32), [[BSWAP1]](s32)
+    ; X86-32-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY [[MV]](s64)
+    ; X86-32-NEXT: RET 0, implicit [[COPY]](s64)
+    %0:_(s64) = IMPLICIT_DEF
+    %1:_(s64) = G_BSWAP %0
+    %2:_(s64) = COPY %1(s64)
+    RET 0, implicit %2
+
+...
+---
+name:            test_bswap_s32
+body:             |
+  bb.1:
+    ; X86-64-LABEL: name: test_bswap_s32
+    ; X86-64: [[DEF:%[0-9]+]]:_(s32) = IMPLICIT_DEF
+    ; X86-64-NEXT: [[BSWAP:%[0-9]+]]:_(s32) = G_BSWAP [[DEF]]
+    ; X86-64-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[BSWAP]](s32)
+    ; X86-64-NEXT: RET 0, implicit [[COPY]](s32)
+    ; X86-32-LABEL: name: test_bswap_s32
+    ; X86-32: [[DEF:%[0-9]+]]:_(s32) = IMPLICIT_DEF
+    ; X86-32-NEXT: [[BSWAP:%[0-9]+]]:_(s32) = G_BSWAP [[DEF]]
+    ; X86-32-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[BSWAP]](s32)
+    ; X86-32-NEXT: RET 0, implicit [[COPY]](s32)
+    %0:_(s32) = IMPLICIT_DEF
+    %1:_(s32) = G_BSWAP %0
+    %2:_(s32) = COPY %1(s32)
+    RET 0, implicit %2
+
+...
+---
+name:            test_bswap_s16
+body:             |
+  bb.1:
+    ; X86-64-LABEL: name: test_bswap_s16
+    ; X86-64: [[DEF:%[0-9]+]]:_(s16) = IMPLICIT_DEF
+    ; X86-64-NEXT: [[ANYEXT:%[0-9]+]]:_(s32) = G_ANYEXT [[DEF]](s16)
+    ; X86-64-NEXT: [[BSWAP:%[0-9]+]]:_(s32) = G_BSWAP [[ANYEXT]]
+    ; X86-64-NEXT: [[C:%[0-9]+]]:_(s8) = G_CONSTANT i8 16
+    ; X86-64-NEXT: [[LSHR:%[0-9]+]]:_(s32) = G_LSHR [[BSWAP]], [[C]](s8)
+    ; X86-64-NEXT: [[TRUNC:%[0-9]+]]:_(s16) = G_TRUNC [[LSHR]](s32)
+    ; X86-64-NEXT: [[COPY:%[0-9]+]]:_(s16) = COPY [[TRUNC]](s16)
+    ; X86-64-NEXT: RET 0, implicit [[COPY]](s16)
+    ; X86-32-LABEL: name: test_bswap_s16
+    ; X86-32: [[DEF:%[0-9]+]]:_(s16) = IMPLICIT_DEF
+    ; X86-32-NEXT: [[ANYEXT:%[0-9]+]]:_(s32) = G_ANYEXT [[DEF]](s16)
+    ; X86-32-NEXT: [[BSWAP:%[0-9]+]]:_(s32) = G_BSWAP [[ANYEXT]]
+    ; X86-32-NEXT: [[C:%[0-9]+]]:_(s8) = G_CONSTANT i8 16
+    ; X86-32-NEXT: [[LSHR:%[0-9]+]]:_(s32) = G_LSHR [[BSWAP]], [[C]](s8)
+    ; X86-32-NEXT: [[TRUNC:%[0-9]+]]:_(s16) = G_TRUNC [[LSHR]](s32)
+    ; X86-32-NEXT: [[COPY:%[0-9]+]]:_(s16) = COPY [[TRUNC]](s16)
+    ; X86-32-NEXT: RET 0, implicit [[COPY]](s16)
+    %0:_(s16) = IMPLICIT_DEF
+    %1:_(s16) = G_BSWAP %0
+    %2:_(s16) = COPY %1(s16)
+    RET 0, implicit %2