diff --git a/llvm/lib/Target/X86/X86LegalizerInfo.h b/llvm/lib/Target/X86/X86LegalizerInfo.h
--- a/llvm/lib/Target/X86/X86LegalizerInfo.h
+++ b/llvm/lib/Target/X86/X86LegalizerInfo.h
@@ -41,6 +41,7 @@
   void setLegalizerInfoSSE1();
   void setLegalizerInfoSSE2();
   void setLegalizerInfoSSE41();
+  void setLegalizerInfoSSE42();
   void setLegalizerInfoAVX();
   void setLegalizerInfoAVX2();
   void setLegalizerInfoAVX512();
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
@@ -65,6 +65,7 @@
   setLegalizerInfoSSE1();
   setLegalizerInfoSSE2();
   setLegalizerInfoSSE41();
+  setLegalizerInfoSSE42();
   setLegalizerInfoAVX();
   setLegalizerInfoAVX2();
   setLegalizerInfoAVX512();
@@ -384,6 +385,27 @@
   LegacyInfo.setAction({G_MUL, v4s32}, LegacyLegalizeActions::Legal);
 }
 
+void X86LegalizerInfo::setLegalizerInfoSSE42() {
+  if (!Subtarget.hasSSE42())
+    return;
+
+  const LLT s16 = LLT::scalar(16);
+  const LLT s32 = LLT::scalar(32);
+  const LLT s64 = LLT::scalar(64);
+
+  // popcount
+  getActionDefinitionsBuilder(G_CTPOP)
+    .legalFor({{s16, s16}, {s32, s32}, {s64, s64}})
+    .widenScalarToNextPow2(1, /*Min=*/16)
+    .clampScalar(1, s16, s64);
+
+  // count leading zeros (LZCNT)
+  getActionDefinitionsBuilder(G_CTLZ)
+    .legalFor({{s16, s16}, {s32, s32}, {s64, s64}})
+    .widenScalarToNextPow2(1, /*Min=*/16)
+    .clampScalar(1, s16, s64);
+}
+
 void X86LegalizerInfo::setLegalizerInfoAVX() {
   if (!Subtarget.hasAVX())
     return;
diff --git a/llvm/test/CodeGen/X86/GlobalISel/legalize-ctpop.mir b/llvm/test/CodeGen/X86/GlobalISel/legalize-ctpop.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/X86/GlobalISel/legalize-ctpop.mir
@@ -0,0 +1,114 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 2
+# RUN: llc -mtriple=x86_64-linux-gnu -mattr=+sse4.2 -run-pass=legalizer %s -o - | FileCheck %s
+
+# test popcount for s16, s32, and s64
+
+---
+name:            test_ctpop35
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctpop35
+    ; CHECK: [[DEF:%[0-9]+]]:_(s35) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[ZEXT:%[0-9]+]]:_(s64) = G_ZEXT [[DEF]](s35)
+    ; CHECK-NEXT: [[CTPOP:%[0-9]+]]:_(s64) = G_CTPOP [[ZEXT]](s64)
+    ; CHECK-NEXT: [[TRUNC:%[0-9]+]]:_(s35) = G_TRUNC [[CTPOP]](s64)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s35) = COPY [[TRUNC]](s35)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s35)
+    %0:_(s35) = IMPLICIT_DEF
+    %1:_(s35) = G_CTPOP %0
+    %2:_(s35) = COPY %1(s35)
+    RET 0, implicit %2
+
+...
+---
+name:            test_ctpop8
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctpop8
+    ; CHECK: [[DEF:%[0-9]+]]:_(s8) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[ZEXT:%[0-9]+]]:_(s16) = G_ZEXT [[DEF]](s8)
+    ; CHECK-NEXT: [[CTPOP:%[0-9]+]]:_(s16) = G_CTPOP [[ZEXT]](s16)
+    ; CHECK-NEXT: [[TRUNC:%[0-9]+]]:_(s8) = G_TRUNC [[CTPOP]](s16)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s8) = COPY [[TRUNC]](s8)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s8)
+    %0:_(s8) = IMPLICIT_DEF
+    %1:_(s8) = G_CTPOP %0
+    %2:_(s8) = COPY %1(s8)
+    RET 0, implicit %2
+
+...
+---
+name:            test_ctpop64
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctpop64
+    ; CHECK: [[DEF:%[0-9]+]]:_(s64) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[CTPOP:%[0-9]+]]:_(s64) = G_CTPOP [[DEF]](s64)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY [[CTPOP]](s64)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s64)
+    %0:_(s64) = IMPLICIT_DEF
+    %1:_(s64) = G_CTPOP %0
+    %2:_(s64) = COPY %1(s64)
+    RET 0, implicit %2
+
+...
+---
+name:            test_ctpop32
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctpop32
+    ; CHECK: [[DEF:%[0-9]+]]:_(s32) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[CTPOP:%[0-9]+]]:_(s32) = G_CTPOP [[DEF]](s32)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTPOP]](s32)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s32)
+    %0:_(s32) = IMPLICIT_DEF
+    %1:_(s32) = G_CTPOP %0
+    %2:_(s32) = COPY %1(s32)
+    RET 0, implicit %2
+
+...
+---
+name:            test_ctpop16
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctpop16
+    ; CHECK: [[DEF:%[0-9]+]]:_(s16) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[CTPOP:%[0-9]+]]:_(s16) = G_CTPOP [[DEF]](s16)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s16) = COPY [[CTPOP]](s16)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s16)
+    %0:_(s16) = IMPLICIT_DEF
+    %1:_(s16) = G_CTPOP %0
+    %2:_(s16) = COPY %1(s16)
+    RET 0, implicit %2
+
+...
diff --git a/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros.mir b/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros.mir
@@ -0,0 +1,118 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 2
+# RUN: llc -mtriple=x86_64-linux-gnu -mattr=+sse4.2 -run-pass=legalizer %s -o - | FileCheck %s
+
+# test count leading zeros for s16, s32, and s64
+
+---
+name:            test_ctlz35
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctlz35
+    ; CHECK: [[DEF:%[0-9]+]]:_(s35) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[ZEXT:%[0-9]+]]:_(s64) = G_ZEXT [[DEF]](s35)
+    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[ZEXT]](s64)
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 29
+    ; CHECK-NEXT: [[SUB:%[0-9]+]]:_(s64) = G_SUB [[CTLZ]], [[C]]
+    ; CHECK-NEXT: [[TRUNC:%[0-9]+]]:_(s35) = G_TRUNC [[SUB]](s64)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s35) = COPY [[TRUNC]](s35)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s35)
+    %0:_(s35) = IMPLICIT_DEF
+    %1:_(s35) = G_CTLZ %0
+    %2:_(s35) = COPY %1(s35)
+    RET 0, implicit %2
+
+...
+---
+name:            test_ctlz8
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctlz8
+    ; CHECK: [[DEF:%[0-9]+]]:_(s8) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[ZEXT:%[0-9]+]]:_(s16) = G_ZEXT [[DEF]](s8)
+    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s16) = G_CTLZ [[ZEXT]](s16)
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s16) = G_CONSTANT i16 8
+    ; CHECK-NEXT: [[SUB:%[0-9]+]]:_(s16) = G_SUB [[CTLZ]], [[C]]
+    ; CHECK-NEXT: [[TRUNC:%[0-9]+]]:_(s8) = G_TRUNC [[SUB]](s16)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s8) = COPY [[TRUNC]](s8)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s8)
+    %0:_(s8) = IMPLICIT_DEF
+    %1:_(s8) = G_CTLZ %0
+    %2:_(s8) = COPY %1(s8)
+    RET 0, implicit %2
+
+...
+---
+name:            test_ctlz64
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctlz64
+    ; CHECK: [[DEF:%[0-9]+]]:_(s64) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[DEF]](s64)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY [[CTLZ]](s64)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s64)
+    %0:_(s64) = IMPLICIT_DEF
+    %1:_(s64) = G_CTLZ %0
+    %2:_(s64) = COPY %1(s64)
+    RET 0, implicit %2
+
+...
+---
+name:            test_ctlz32
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctlz32
+    ; CHECK: [[DEF:%[0-9]+]]:_(s32) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s32) = G_CTLZ [[DEF]](s32)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTLZ]](s32)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s32)
+    %0:_(s32) = IMPLICIT_DEF
+    %1:_(s32) = G_CTLZ %0
+    %2:_(s32) = COPY %1(s32)
+    RET 0, implicit %2
+
+...
+---
+name:            test_ctlz16
+alignment:       16
+legalized:       false
+regBankSelected: false
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_ctlz16
+    ; CHECK: [[DEF:%[0-9]+]]:_(s16) = IMPLICIT_DEF
+    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s16) = G_CTLZ [[DEF]](s16)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s16) = COPY [[CTLZ]](s16)
+    ; CHECK-NEXT: RET 0, implicit [[COPY]](s16)
+    %0:_(s16) = IMPLICIT_DEF
+    %1:_(s16) = G_CTLZ %0
+    %2:_(s16) = COPY %1(s16)
+    RET 0, implicit %2
+
+...