diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 4942c997682..45c5f56f447 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -948,7 +948,6 @@ extern "C" {
 
     // Operations on other types
     pub fn LLVMVoidTypeInContext(C: &Context) -> &Type;
-    pub fn LLVMX86MMXTypeInContext(C: &Context) -> &Type;
     pub fn LLVMRustMetadataTypeInContext(C: &Context) -> &Type;
 
     // Operations on all values
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index f0b50459837..900f2df383a 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -203,7 +203,6 @@ const X86_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
     ("fma", None),
     ("fxsr", None),
     ("lzcnt", None),
-    ("mmx", Some(sym::mmx_target_feature)),
     ("movbe", Some(sym::movbe_target_feature)),
     ("pclmulqdq", None),
     ("popcnt", None),
diff --git a/compiler/rustc_codegen_llvm/src/type_.rs b/compiler/rustc_codegen_llvm/src/type_.rs
index 3b53b4fe77b..a43724fd495 100644
--- a/compiler/rustc_codegen_llvm/src/type_.rs
+++ b/compiler/rustc_codegen_llvm/src/type_.rs
@@ -62,10 +62,6 @@ impl CodegenCx<'ll, 'tcx> {
         unsafe { llvm::LLVMIntTypeInContext(self.llcx, num_bits as c_uint) }
     }
 
-    crate fn type_x86_mmx(&self) -> &'ll Type {
-        unsafe { llvm::LLVMX86MMXTypeInContext(self.llcx) }
-    }
-
     crate fn type_vector(&self, ty: &'ll Type, len: u64) -> &'ll Type {
         unsafe { llvm::LLVMVectorType(ty, len as c_uint) }
     }
diff --git a/compiler/rustc_codegen_llvm/src/type_of.rs b/compiler/rustc_codegen_llvm/src/type_of.rs
index 12901de6048..e0754d21df1 100644
--- a/compiler/rustc_codegen_llvm/src/type_of.rs
+++ b/compiler/rustc_codegen_llvm/src/type_of.rs
@@ -21,23 +21,8 @@ fn uncached_llvm_type<'a, 'tcx>(
     match layout.abi {
         Abi::Scalar(_) => bug!("handled elsewhere"),
         Abi::Vector { ref element, count } => {
-            // LLVM has a separate type for 64-bit SIMD vectors on X86 called
-            // `x86_mmx` which is needed for some SIMD operations. As a bit of a
-            // hack (all SIMD definitions are super unstable anyway) we
-            // recognize any one-element SIMD vector as "this should be an
-            // x86_mmx" type. In general there shouldn't be a need for other
-            // one-element SIMD vectors, so it's assumed this won't clash with
-            // much else.
-            let use_x86_mmx = count == 1
-                && layout.size.bits() == 64
-                && (cx.sess().target.target.arch == "x86"
-                    || cx.sess().target.target.arch == "x86_64");
-            if use_x86_mmx {
-                return cx.type_x86_mmx();
-            } else {
-                let element = layout.scalar_llvm_type_at(cx, element, Size::ZERO);
-                return cx.type_vector(element, count);
-            }
+            let element = layout.scalar_llvm_type_at(cx, element, Size::ZERO);
+            return cx.type_vector(element, count);
         }
         Abi::ScalarPair(..) => {
             return cx.type_struct(
diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index d4664292a0c..6452bda293e 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -229,7 +229,6 @@ declare_features! (
     (active, powerpc_target_feature, "1.27.0", Some(44839), None),
     (active, mips_target_feature, "1.27.0", Some(44839), None),
     (active, avx512_target_feature, "1.27.0", Some(44839), None),
-    (active, mmx_target_feature, "1.27.0", Some(44839), None),
     (active, sse4a_target_feature, "1.27.0", Some(44839), None),
     (active, tbm_target_feature, "1.27.0", Some(44839), None),
     (active, wasm_target_feature, "1.30.0", Some(44839), None),
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 407663e5757..ce6cc4ab035 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -677,7 +677,6 @@ symbols! {
         minnumf32,
         minnumf64,
         mips_target_feature,
-        mmx_target_feature,
         module,
         module_path,
         more_struct_aliases,
diff --git a/compiler/rustc_typeck/src/collect.rs b/compiler/rustc_typeck/src/collect.rs
index 9b8427a4695..ad2389a434d 100644
--- a/compiler/rustc_typeck/src/collect.rs
+++ b/compiler/rustc_typeck/src/collect.rs
@@ -2361,7 +2361,6 @@ fn from_target_feature(
                 Some(sym::mips_target_feature) => rust_features.mips_target_feature,
                 Some(sym::riscv_target_feature) => rust_features.riscv_target_feature,
                 Some(sym::avx512_target_feature) => rust_features.avx512_target_feature,
-                Some(sym::mmx_target_feature) => rust_features.mmx_target_feature,
                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 3bddc3772e6..dd247e49234 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -132,7 +132,6 @@
 #![feature(unwind_attributes)]
 #![feature(variant_count)]
 #![cfg_attr(bootstrap, feature(doc_alias))]
-#![feature(mmx_target_feature)]
 #![feature(tbm_target_feature)]
 #![feature(sse4a_target_feature)]
 #![feature(arm_target_feature)]
diff --git a/src/test/codegen/x86_mmx.rs b/src/test/codegen/x86_mmx.rs
deleted file mode 100644
index 9a58ef1c37a..00000000000
--- a/src/test/codegen/x86_mmx.rs
+++ /dev/null
@@ -1,27 +0,0 @@
-// ignore-arm
-// ignore-aarch64
-// ignore-emscripten
-// ignore-mips
-// ignore-mips64
-// ignore-powerpc
-// ignore-powerpc64
-// ignore-powerpc64le
-// ignore-riscv64
-// ignore-sparc
-// ignore-sparc64
-// ignore-s390x
-// compile-flags: -O
-
-#![feature(repr_simd)]
-#![crate_type="lib"]
-
-#[repr(simd)]
-#[derive(Clone, Copy)]
-pub struct i8x8(u64);
-
-#[no_mangle]
-pub fn a(a: &mut i8x8, b: i8x8) -> i8x8 {
-    // CHECK-LABEL: define void @a(x86_mmx*{{.*}}, x86_mmx*{{.*}}, x86_mmx*{{.*}})
-    *a = b;
-    return b
-}
diff --git a/src/test/ui/auxiliary/using-target-feature-unstable.rs b/src/test/ui/auxiliary/using-target-feature-unstable.rs
index 78645c284f1..2682028936c 100644
--- a/src/test/ui/auxiliary/using-target-feature-unstable.rs
+++ b/src/test/ui/auxiliary/using-target-feature-unstable.rs
@@ -1,5 +1,5 @@
-#![feature(mmx_target_feature)]
+#![feature(avx512_target_feature)]
 
 #[inline]
-#[target_feature(enable = "mmx")]
+#[target_feature(enable = "avx512ifma")]
 pub unsafe fn foo() {}
diff --git a/src/test/ui/target-feature/gate.rs b/src/test/ui/target-feature/gate.rs
index 10fbba36d3f..e4b78c76e16 100644
--- a/src/test/ui/target-feature/gate.rs
+++ b/src/test/ui/target-feature/gate.rs
@@ -19,7 +19,6 @@
 // gate-test-aarch64_target_feature
 // gate-test-hexagon_target_feature
 // gate-test-mips_target_feature
-// gate-test-mmx_target_feature
 // gate-test-wasm_target_feature
 // gate-test-adx_target_feature
 // gate-test-cmpxchg16b_target_feature
@@ -30,7 +29,6 @@
 
 #[target_feature(enable = "avx512bw")]
 //~^ ERROR: currently unstable
-unsafe fn foo() {
-}
+unsafe fn foo() {}
 
 fn main() {}
diff --git a/src/test/ui/target-feature/gate.stderr b/src/test/ui/target-feature/gate.stderr
index 2d6abcc0a01..2384a00aa47 100644
--- a/src/test/ui/target-feature/gate.stderr
+++ b/src/test/ui/target-feature/gate.stderr
@@ -1,5 +1,5 @@
 error[E0658]: the target feature `avx512bw` is currently unstable
-  --> $DIR/gate.rs:31:18
+  --> $DIR/gate.rs:30:18
    |
 LL | #[target_feature(enable = "avx512bw")]
    |                  ^^^^^^^^^^^^^^^^^^^