diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltinX86.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltinX86.cpp
index a30c79a83751a..978fee7dbec9d 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltinX86.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltinX86.cpp
@@ -144,10 +144,13 @@ mlir::Value CIRGenFunction::emitX86BuiltinExpr(unsigned builtinID,
   case X86::BI__builtin_ia32_undef128:
   case X86::BI__builtin_ia32_undef256:
   case X86::BI__builtin_ia32_undef512:
-    cgm.errorNYI(expr->getSourceRange(),
-                 std::string("unimplemented X86 builtin call: ") +
-                     getContext().BuiltinInfo.getName(builtinID));
-    return {};
+    // The x86 definition of "undef" is not the same as the LLVM definition
+    // (PR32176). We leave optimizing away an unnecessary zero constant to the
+    // IR optimizer and backend.
+    // TODO: If we had a "freeze" IR instruction to generate a fixed undef
+    //  value, we should use that here instead of a zero.
+    return builder.getNullValue(convertType(expr->getType()),
+                                getLoc(expr->getExprLoc()));
   case X86::BI__builtin_ia32_vec_ext_v4hi:
   case X86::BI__builtin_ia32_vec_ext_v16qi:
   case X86::BI__builtin_ia32_vec_ext_v8hi:
diff --git a/clang/test/CIR/CodeGen/X86/avx-builtins.c b/clang/test/CIR/CodeGen/X86/avx-builtins.c
new file mode 100644
index 0000000000000..82fa4358dc400
--- /dev/null
+++ b/clang/test/CIR/CodeGen/X86/avx-builtins.c
@@ -0,0 +1,76 @@
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx -fclangir -emit-cir -o %t.cir -Wall -Werror
+// RUN: FileCheck --check-prefixes=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx -fno-signed-char -fclangir -emit-cir -o %t.cir -Wall -Werror
+// RUN: FileCheck --check-prefixes=CIR --input-file=%t.cir %s
+
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx -fclangir -emit-llvm -o %t.ll -Wall -Werror
+// RUN: FileCheck --check-prefixes=LLVM --input-file=%t.ll %s
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx -fno-signed-char -fclangir -emit-llvm -o %t.ll -Wall -Werror
+// RUN: FileCheck --check-prefixes=LLVM --input-file=%t.ll %s
+
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx -fclangir -emit-cir -o %t.cir -Wall -Werror
+// RUN: FileCheck --check-prefixes=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx -fno-signed-char -fclangir -emit-cir -o %t.cir -Wall -Werror
+// RUN: FileCheck --check-prefixes=CIR --input-file=%t.cir %s
+
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx -fclangir -emit-llvm -o %t.ll -Wall -Werror
+// RUN: FileCheck --check-prefixes=LLVM --input-file=%t.ll %s
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx -fno-signed-char -fclangir -emit-llvm -o %t.ll -Wall -Werror
+// RUN: FileCheck --check-prefixes=LLVM --input-file=%t.ll %s
+
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +avx -emit-llvm -o - -Wall -Werror | FileCheck %s --check-prefixes=OGCG
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +avx -fno-signed-char -emit-llvm -o - -Wall -Werror | FileCheck %s --check-prefixes=OGCG
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +avx -emit-llvm -o - -Wall -Werror | FileCheck %s --check-prefixes=OGCG
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +avx -fno-signed-char -emit-llvm -o - -Wall -Werror | FileCheck %s --check-prefixes=OGCG
+
+// This test mimics clang/test/CodeGen/X86/avx-builtins.c, which eventually
+// CIR shall be able to support fully.
+
+#include <immintrin.h>
+
+__m256 test_mm256_undefined_ps(void) {
+  // CIR-LABEL: _mm256_undefined_ps
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<4 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<4 x !cir.double> -> !cir.vector<8 x !cir.float>
+  // CIR: cir.return %{{.*}} : !cir.vector<8 x !cir.float>
+
+  // LLVM-LABEL: test_mm256_undefined_ps
+  // LLVM: store <8 x float> zeroinitializer, ptr %[[A:.*]], align 32
+  // LLVM: %{{.*}} = load <8 x float>, ptr %[[A]], align 32
+  // LLVM: ret <8 x float> %{{.*}}
+
+  // OGCG-LABEL: test_mm256_undefined_ps
+  // OGCG: ret <8 x float> zeroinitializer
+  return _mm256_undefined_ps();
+}
+
+__m256d test_mm256_undefined_pd(void) {
+  // CIR-LABEL: _mm256_undefined_pd
+  // CIR: %{{.*}} = cir.const #cir.zero : !cir.vector<4 x !cir.double>
+  // CIR: cir.return %{{.*}} : !cir.vector<4 x !cir.double>
+
+  // LLVM-LABEL: test_mm256_undefined_pd
+  // LLVM: store <4 x double> zeroinitializer, ptr %[[A:.*]], align 32
+  // LLVM: %{{.*}} = load <4 x double>, ptr %[[A]], align 32
+  // LLVM: ret <4 x double> %{{.*}}
+
+  // OGCG-LABEL: test_mm256_undefined_pd
+  // OGCG: ret <4 x double> zeroinitializer
+  return _mm256_undefined_pd();
+}
+
+__m256i test_mm256_undefined_si256(void) {
+  // CIR-LABEL: _mm256_undefined_si256
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<4 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<4 x !cir.double> -> !cir.vector<4 x !s64i>
+  // CIR: cir.return %{{.*}} : !cir.vector<4 x !s64i>
+
+  // LLVM-LABEL: test_mm256_undefined_si256
+  // LLVM: store <4 x i64> zeroinitializer, ptr %[[A:.*]], align 32
+  // LLVM: %{{.*}} = load <4 x i64>, ptr %[[A]], align 32
+  // LLVM: ret <4 x i64> %{{.*}}
+
+  // OGCG-LABEL: test_mm256_undefined_si256
+  // OGCG: ret <4 x i64> zeroinitializer
+  return _mm256_undefined_si256();
+}
\ No newline at end of file
diff --git a/clang/test/CIR/CodeGen/X86/avx10_2_512bf16-builtins.c b/clang/test/CIR/CodeGen/X86/avx10_2_512bf16-builtins.c
new file mode 100644
index 0000000000000..e4501889c2d60
--- /dev/null
+++ b/clang/test/CIR/CodeGen/X86/avx10_2_512bf16-builtins.c
@@ -0,0 +1,28 @@
+// RUN: %clang_cc1 -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx10.2-512 -fclangir -emit-cir -o %t.cir -Wno-invalid-feature-combination -Wall -Werror -Wsign-conversion
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx10.2-512 -fclangir -emit-llvm -o %t.ll -Wno-invalid-feature-combination -Wall -Werror -Wsign-conversion
+// RUN: FileCheck --check-prefixes=LLVM --input-file=%t.ll %s
+
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx10.2 -emit-llvm -o - -Wall -Werror | FileCheck %s -check-prefix=OGCG
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx10.2 -emit-llvm -o - -Wall -Werror | FileCheck %s -check-prefix=OGCG
+
+#include <immintrin.h>
+
+__m512bh test_mm512_undefined_pbh(void) {
+  // CIR-LABEL: _mm512_undefined_pbh
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<8 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<8 x !cir.double> -> !cir.vector<32 x !cir.bf16>
+  // CIR: cir.return %{{.*}} : !cir.vector<32 x !cir.bf16>
+
+  // CIR-LABEL: cir.func {{.*}}test_mm512_undefined_pbh
+  // CIR: call @_mm512_undefined_pbh
+
+  // LLVM-LABEL: test_mm512_undefined_pbh
+  // LLVM: store <32 x bfloat> zeroinitializer, ptr %[[A:.*]], align 64
+  // LLVM: %{{.*}} = load <32 x bfloat>, ptr %[[A]], align 64
+  // LLVM: ret <32 x bfloat> %{{.*}}
+
+  // OGCG-LABEL: test_mm512_undefined_pbh
+  // OGCG: ret <32 x bfloat> zeroinitializer
+  return _mm512_undefined_pbh();
+}
diff --git a/clang/test/CIR/CodeGen/X86/avx10_2bf16-builtins.c b/clang/test/CIR/CodeGen/X86/avx10_2bf16-builtins.c
new file mode 100644
index 0000000000000..4dac4fa2fe811
--- /dev/null
+++ b/clang/test/CIR/CodeGen/X86/avx10_2bf16-builtins.c
@@ -0,0 +1,47 @@
+// RUN: %clang_cc1 -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx10.2-256 -fclangir -emit-cir -o %t.cir -Wno-invalid-feature-combination -Wall -Werror -Wsign-conversion
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx10.2-256 -fclangir -emit-llvm -o %t.ll -Wno-invalid-feature-combination -Wall -Werror -Wsign-conversion
+// RUN: FileCheck --check-prefixes=LLVM --input-file=%t.ll %s
+
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx10.2 -emit-llvm -o - -Wall -Werror | FileCheck %s -check-prefix=OGCG
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx10.2 -emit-llvm -o - -Wall -Werror | FileCheck %s -check-prefix=OGCG
+
+#include <immintrin.h>
+
+__m128bh test_mm_undefined_pbh(void) {
+  // CIR-LABEL: _mm_undefined_pbh
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<2 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<2 x !cir.double> -> !cir.vector<8 x !cir.bf16>
+  // CIR: cir.return %{{.*}} : !cir.vector<8 x !cir.bf16>
+
+  // CIR-LABEL: cir.func {{.*}}test_mm_undefined_pbh
+  // CIR: call @_mm_undefined_pbh
+
+  // LLVM-LABEL: @test_mm_undefined_pbh
+  // LLVM: store <8 x bfloat> zeroinitializer, ptr %[[A:.*]], align 16
+  // LLVM: %{{.*}} = load <8 x bfloat>, ptr %[[A]], align 16
+  // LLVM: ret <8 x bfloat> %{{.*}}
+
+  // OGCG-LABEL: test_mm_undefined_pbh
+  // OGCG: ret <8 x bfloat> zeroinitializer
+  return _mm_undefined_pbh();
+}
+
+__m256bh test_mm256_undefined_pbh(void) {
+  // CIR-LABEL: _mm256_undefined_pbh
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<4 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<4 x !cir.double> -> !cir.vector<16 x !cir.bf16>
+  // CIR: cir.return %{{.*}} : !cir.vector<16 x !cir.bf16>
+
+  // CIR-LABEL: cir.func {{.*}}test_mm256_undefined_pbh
+  // CIR: call @_mm256_undefined_pbh
+
+  // LLVM-LABEL: @test_mm256_undefined_pbh
+  // LLVM: store <16 x bfloat> zeroinitializer, ptr %[[A:.*]], align 32
+  // LLVM: %{{.*}} = load <16 x bfloat>, ptr %[[A]], align 32
+  // LLVM: ret <16 x bfloat> %{{.*}}
+
+  // OGCG-LABEL: test_mm256_undefined_pbh
+  // OGCG: ret <16 x bfloat> zeroinitializer
+  return _mm256_undefined_pbh();
+}
\ No newline at end of file
diff --git a/clang/test/CIR/CodeGen/X86/avx512f-builtins.c b/clang/test/CIR/CodeGen/X86/avx512f-builtins.c
new file mode 100644
index 0000000000000..dc54a87856a7c
--- /dev/null
+++ b/clang/test/CIR/CodeGen/X86/avx512f-builtins.c
@@ -0,0 +1,79 @@
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx512f -fclangir -emit-cir -o %t.cir -Wall -Werror -Wsign-conversion
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx512f -fclangir -emit-llvm -o %t.ll -Wall -Werror -Wsign-conversion
+// RUN: FileCheck --check-prefixes=LLVM --input-file=%t.ll %s
+
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx512f -fclangir -emit-cir -o %t.cir -Wall -Werror -Wsign-conversion
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx512f -fclangir -emit-llvm -o %t.ll -Wall -Werror -Wsign-conversion
+// RUN: FileCheck --check-prefixes=LLVM --input-file=%t.ll %s
+
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +avx512f -emit-llvm -o - -Wall -Werror -Wsign-conversion | FileCheck %s --check-prefixes=OGCG
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -fms-extensions -fms-compatibility -ffreestanding %s -triple=x86_64-windows-msvc -target-feature +avx512f -emit-llvm -o - -Wall -Werror -Wsign-conversion | FileCheck %s --check-prefixes=OGCG
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +avx512f -emit-llvm -o - -Wall -Werror -Wsign-conversion | FileCheck %s --check-prefixes=OGCG
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -fms-extensions -fms-compatibility -ffreestanding %s -triple=x86_64-windows-msvc -target-feature +avx512f -emit-llvm -o - -Wall -Werror -Wsign-conversion | FileCheck %s --check-prefixes=OGCG
+
+#include <immintrin.h>
+
+__m512 test_mm512_undefined(void) {
+  // CIR-LABEL: _mm512_undefined
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<8 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<8 x !cir.double> -> !cir.vector<16 x !cir.float>
+  // CIR: cir.return %{{.*}} : !cir.vector<16 x !cir.float>
+
+  // LLVM-LABEL: test_mm512_undefined
+  // LLVM: store <16 x float> zeroinitializer, ptr %[[A:.*]], align 64
+  // LLVM: %{{.*}} = load <16 x float>, ptr %[[A]], align 64
+  // LLVM: ret <16 x float> %{{.*}}
+
+  // OGCG-LABEL: test_mm512_undefined
+  // OGCG: ret <16 x float> zeroinitializer
+  return _mm512_undefined();
+}
+
+__m512 test_mm512_undefined_ps(void) {
+  // CIR-LABEL: _mm512_undefined_ps
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<8 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<8 x !cir.double> -> !cir.vector<16 x !cir.float>
+  // CIR: cir.return %{{.*}} : !cir.vector<16 x !cir.float>
+
+  // LLVM-LABEL: test_mm512_undefined_ps
+  // LLVM: store <16 x float> zeroinitializer, ptr %[[A:.*]], align 64
+  // LLVM: %{{.*}} = load <16 x float>, ptr %[[A]], align 64
+  // LLVM: ret <16 x float> %{{.*}}
+
+  // OGCG-LABEL: test_mm512_undefined_ps
+  // OGCG: ret <16 x float> zeroinitializer
+  return _mm512_undefined_ps();
+}
+
+__m512d test_mm512_undefined_pd(void) {
+  // CIR-LABEL: _mm512_undefined_pd
+  // CIR: %{{.*}} = cir.const #cir.zero : !cir.vector<8 x !cir.double>
+  // CIR: cir.return %{{.*}} : !cir.vector<8 x !cir.double>
+
+  // LLVM-LABEL: test_mm512_undefined_pd
+  // LLVM: store <8 x double> zeroinitializer, ptr %[[A:.*]], align 64
+  // LLVM: %{{.*}} = load <8 x double>, ptr %[[A]], align 64
+  // LLVM: ret <8 x double> %{{.*}}
+
+  // OGCG-LABEL: test_mm512_undefined_pd
+  // OGCG: ret <8 x double> zeroinitializer
+  return _mm512_undefined_pd();
+}
+
+__m512i test_mm512_undefined_epi32(void) {
+  // CIR-LABEL: _mm512_undefined_epi32
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<8 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<8 x !cir.double> -> !cir.vector<8 x !s64i>
+  // CIR: cir.return %{{.*}} : !cir.vector<8 x !s64i>
+
+  // LLVM-LABEL: test_mm512_undefined_epi32
+  // LLVM: store <8 x i64> zeroinitializer, ptr %[[A:.*]], align 64
+  // LLVM: %{{.*}} = load <8 x i64>, ptr %[[A]], align 64
+  // LLVM: ret <8 x i64> %{{.*}}
+
+  // OGCG-LABEL: test_mm512_undefined_epi32
+  // OGCG: ret <8 x i64> zeroinitializer
+  return _mm512_undefined_epi32();
+}
diff --git a/clang/test/CIR/CodeGen/X86/avx512fp16-builtins.c b/clang/test/CIR/CodeGen/X86/avx512fp16-builtins.c
new file mode 100644
index 0000000000000..161fc45b2a32d
--- /dev/null
+++ b/clang/test/CIR/CodeGen/X86/avx512fp16-builtins.c
@@ -0,0 +1,66 @@
+// RUN: %clang_cc1 -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx512fp16 -fclangir -emit-cir -o %t.cir -Wall -Werror
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx512fp16 -fclangir -emit-llvm -o %t.ll  -Wall -Werror
+// RUN: FileCheck --check-prefixes=LLVM --input-file=%t.ll %s
+
+// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx512fp16 -emit-llvm -o - -Wall -Werror | FileCheck %s -check-prefix=OGCG
+// RUN: %clang_cc1 -x c++ -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx512fp16 -emit-llvm -o - -Wall -Werror | FileCheck %s -check-prefix=OGCG
+
+#include <immintrin.h>
+
+__m128h test_mm_undefined_ph(void) {
+  // CIR-LABEL: _mm_undefined_ph
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<2 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<2 x !cir.double> -> !cir.vector<8 x !cir.f16>
+  // CIR: cir.return %{{.*}} : !cir.vector<8 x !cir.f16>
+
+  // CIR-LABEL: cir.func {{.*}}test_mm_undefined_ph
+  // CIR: call @_mm_undefined_ph
+
+  // LLVM-LABEL: @test_mm_undefined_ph
+  // LLVM: store <8 x half> zeroinitializer, ptr %[[A:.*]], align 16
+  // LLVM: %{{.*}} = load <8 x half>, ptr %[[A]], align 16
+  // LLVM: ret <8 x half> %{{.*}}
+
+  // OGCG-LABEL: test_mm_undefined_ph
+  // OGCG: ret <8 x half> zeroinitializer
+  return _mm_undefined_ph();
+}
+
+__m256h test_mm256_undefined_ph(void) {
+  // CIR-LABEL: _mm256_undefined_ph
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<4 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<4 x !cir.double> -> !cir.vector<16 x !cir.f16>
+  // CIR: cir.return %{{.*}} : !cir.vector<16 x !cir.f16>
+
+  // CIR-LABEL: cir.func {{.*}}test_mm256_undefined_ph
+  // CIR: call @_mm256_undefined_ph
+
+  // LLVM-LABEL: @test_mm256_undefined_ph
+  // LLVM: store <16 x half> zeroinitializer, ptr %[[A:.*]], align 32
+  // LLVM: %{{.*}} = load <16 x half>, ptr %[[A]], align 32
+  // LLVM: ret <16 x half> %{{.*}}
+
+  // OGCG-LABEL: test_mm256_undefined_ph
+  // OGCG: ret <16 x half> zeroinitializer
+  return _mm256_undefined_ph();
+}
+
+__m512h test_mm512_undefined_ph(void) {
+  // CIR-LABEL: _mm512_undefined_ph
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<8 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<8 x !cir.double> -> !cir.vector<32 x !cir.f16>
+  // CIR: cir.return %{{.*}} : !cir.vector<32 x !cir.f16>
+
+  // CIR-LABEL: cir.func {{.*}}test_mm512_undefined_ph
+  // CIR: call @_mm512_undefined_ph
+
+  // LLVM-LABEL: @test_mm512_undefined_ph
+  // LLVM: store <32 x half> zeroinitializer, ptr %[[A:.*]], align 64
+  // LLVM: %{{.*}} = load <32 x half>, ptr %[[A]], align 64
+  // LLVM: ret <32 x half> %{{.*}}
+
+  // OGCG-LABEL: test_mm512_undefined_ph
+  // OGCG: ret <32 x half> zeroinitializer
+  return _mm512_undefined_ph();
+}
\ No newline at end of file
diff --git a/clang/test/CIR/CodeGen/X86/sse-builtins.c b/clang/test/CIR/CodeGen/X86/sse-builtins.c
index 04e69a9990159..c893859b297cc 100644
--- a/clang/test/CIR/CodeGen/X86/sse-builtins.c
+++ b/clang/test/CIR/CodeGen/X86/sse-builtins.c
@@ -55,3 +55,19 @@ void test_mm_sfence(void) {
   // LLVM: call void @llvm.x86.sse.sfence()
   // OGCG: call void @llvm.x86.sse.sfence()
 }
+
+__m128 test_mm_undefined_ps(void) {
+  // CIR-LABEL: _mm_undefined_ps
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<2 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<2 x !cir.double> -> !cir.vector<4 x !cir.float>
+  // CIR: cir.return %{{.*}} : !cir.vector<4 x !cir.float>
+
+  // LLVM-LABEL: test_mm_undefined_ps
+  // LLVM: store <4 x float> zeroinitializer, ptr %[[A:.*]], align 16
+  // LLVM: %{{.*}} = load <4 x float>, ptr %[[A]], align 16
+  // LLVM: ret <4 x float> %{{.*}}
+
+  // OGCG-LABEL: test_mm_undefined_ps
+  // OGCG: ret <4 x float> zeroinitializer
+  return _mm_undefined_ps();
+}
diff --git a/clang/test/CIR/CodeGen/X86/sse2-builtins.c b/clang/test/CIR/CodeGen/X86/sse2-builtins.c
index 9ec8f7a9bf4fe..f5e07cdc28ccd 100644
--- a/clang/test/CIR/CodeGen/X86/sse2-builtins.c
+++ b/clang/test/CIR/CodeGen/X86/sse2-builtins.c
@@ -16,6 +16,43 @@
 
 #include <immintrin.h>
 
+__m128d test_mm_undefined_pd(void) {
+  // CIR-LABEL: _mm_undefined_pd
+  // CIR: %{{.*}} = cir.const #cir.zero : !cir.vector<2 x !cir.double>
+  // CIR: cir.return %{{.*}} : !cir.vector<2 x !cir.double>
+
+  // CIR-LABEL: cir.func {{.*}}test_mm_undefined_pd
+  // CIR: call @_mm_undefined_pd
+
+  // LLVM-LABEL: test_mm_undefined_pd
+  // LLVM: store <2 x double> zeroinitializer, ptr %[[A:.*]], align 16
+  // LLVM: %{{.*}} = load <2 x double>, ptr %[[A]], align 16
+  // LLVM: ret <2 x double> %{{.*}}
+
+  // OGCG-LABEL: test_mm_undefined_pd
+  // OGCG: ret <2 x double> zeroinitializer
+  return _mm_undefined_pd();
+}
+
+__m128i test_mm_undefined_si128(void) {
+  // CIR-LABEL: _mm_undefined_si128
+  // CIR: %[[A:.*]] = cir.const #cir.zero : !cir.vector<2 x !cir.double>
+  // CIR: %{{.*}} = cir.cast bitcast %[[A]] : !cir.vector<2 x !cir.double> ->
+  // CIR: cir.return %{{.*}} :
+
+  // CIR-LABEL: cir.func {{.*}}test_mm_undefined_si128
+  // CIR: call @_mm_undefined_si128
+
+  // LLVM-LABEL: test_mm_undefined_si128
+  // LLVM: store <2 x i64> zeroinitializer, ptr %[[A:.*]], align 16
+  // LLVM: %{{.*}} = load <2 x i64>, ptr %[[A]], align 16
+  // LLVM: ret <2 x i64> %{{.*}}
+
+  // OGCG-LABEL: test_mm_undefined_si128
+  // OGCG: ret <2 x i64> zeroinitializer
+  return _mm_undefined_si128();
+}
+
 // Lowering to pextrw requires optimization.
 int test_mm_extract_epi16(__m128i A) {
   // CIR-LABEL: test_mm_extract_epi16