diff --git a/compiler/rustc_codegen_llvm/messages.ftl b/compiler/rustc_codegen_llvm/messages.ftl
index c0cfe39f1e0a4..7a86ddc7556a0 100644
--- a/compiler/rustc_codegen_llvm/messages.ftl
+++ b/compiler/rustc_codegen_llvm/messages.ftl
@@ -76,8 +76,8 @@ codegen_llvm_target_machine = could not create LLVM TargetMachine for triple: {$
 codegen_llvm_target_machine_with_llvm_err = could not create LLVM TargetMachine for triple: {$triple}: {$llvm_err}
 
 codegen_llvm_unknown_ctarget_feature =
-    unknown feature specified for `-Ctarget-feature`: `{$feature}`
-    .note = it is still passed through to the codegen backend
+    unknown and unstable feature specified for `-Ctarget-feature`: `{$feature}`
+    .note = it is still passed through to the codegen backend, but use of this feature might be unsound and the behavior of this feature can change in the future
     .possible_feature = you might have meant: `{$rust_feature}`
     .consider_filing_feature_request = consider filing a feature request
 
@@ -87,6 +87,10 @@ codegen_llvm_unknown_ctarget_feature_prefix =
 
 codegen_llvm_unknown_debuginfo_compression = unknown debuginfo compression algorithm {$algorithm} - will fall back to uncompressed debuginfo
 
+codegen_llvm_unstable_ctarget_feature =
+    unstable feature specified for `-Ctarget-feature`: `{$feature}`
+    .note = this feature is not stably supported; its behavior can change in the future
+
 codegen_llvm_write_bytecode = failed to write bytecode to {$path}: {$err}
 
 codegen_llvm_write_ir = failed to write LLVM IR to {$path}
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index 665d195790c2d..10ca5ad802a05 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -26,6 +26,13 @@ pub(crate) struct UnknownCTargetFeature<'a> {
     pub rust_feature: PossibleFeature<'a>,
 }
 
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_unstable_ctarget_feature)]
+#[note]
+pub(crate) struct UnstableCTargetFeature<'a> {
+    pub feature: &'a str,
+}
+
 #[derive(Subdiagnostic)]
 pub(crate) enum PossibleFeature<'a> {
     #[help(codegen_llvm_possible_feature)]
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index 7c8ef67ffd10e..cc4ccaf19c282 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -1,7 +1,7 @@
 use crate::back::write::create_informational_target_machine;
 use crate::errors::{
     PossibleFeature, TargetFeatureDisableOrEnable, UnknownCTargetFeature,
-    UnknownCTargetFeaturePrefix,
+    UnknownCTargetFeaturePrefix, UnstableCTargetFeature,
 };
 use crate::llvm;
 use libc::c_int;
@@ -531,25 +531,34 @@ pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<Str
             };
 
             let feature = backend_feature_name(s)?;
-            // Warn against use of LLVM specific feature names on the CLI.
-            if diagnostics && !supported_features.iter().any(|&(v, _)| v == feature) {
-                let rust_feature = supported_features.iter().find_map(|&(rust_feature, _)| {
-                    let llvm_features = to_llvm_features(sess, rust_feature);
-                    if llvm_features.contains(&feature) && !llvm_features.contains(&rust_feature) {
-                        Some(rust_feature)
+            // Warn against use of LLVM specific feature names and unstable features on the CLI.
+            if diagnostics {
+                let feature_state = supported_features.iter().find(|&&(v, _)| v == feature);
+                if feature_state.is_none() {
+                    let rust_feature = supported_features.iter().find_map(|&(rust_feature, _)| {
+                        let llvm_features = to_llvm_features(sess, rust_feature);
+                        if llvm_features.contains(&feature)
+                            && !llvm_features.contains(&rust_feature)
+                        {
+                            Some(rust_feature)
+                        } else {
+                            None
+                        }
+                    });
+                    let unknown_feature = if let Some(rust_feature) = rust_feature {
+                        UnknownCTargetFeature {
+                            feature,
+                            rust_feature: PossibleFeature::Some { rust_feature },
+                        }
                     } else {
-                        None
-                    }
-                });
-                let unknown_feature = if let Some(rust_feature) = rust_feature {
-                    UnknownCTargetFeature {
-                        feature,
-                        rust_feature: PossibleFeature::Some { rust_feature },
-                    }
-                } else {
-                    UnknownCTargetFeature { feature, rust_feature: PossibleFeature::None }
-                };
-                sess.emit_warning(unknown_feature);
+                        UnknownCTargetFeature { feature, rust_feature: PossibleFeature::None }
+                    };
+                    sess.emit_warning(unknown_feature);
+                } else if feature_state.is_some_and(|(_name, feature_gate)| feature_gate.is_some())
+                {
+                    // An unstable feature. Warn about using it.
+                    sess.emit_warning(UnstableCTargetFeature { feature });
+                }
             }
 
             if diagnostics {
diff --git a/compiler/rustc_codegen_ssa/src/target_features.rs b/compiler/rustc_codegen_ssa/src/target_features.rs
index 9c053338c8537..2936f1de3cbf8 100644
--- a/compiler/rustc_codegen_ssa/src/target_features.rs
+++ b/compiler/rustc_codegen_ssa/src/target_features.rs
@@ -23,6 +23,15 @@ pub const RUSTC_SPECIFIC_FEATURES: &[&str] = &["crt-static"];
 // check whether they're named already elsewhere in rust
 // e.g. in stdarch and whether the given name matches LLVM's
 // if it doesn't, to_llvm_feature in llvm_util in rustc_codegen_llvm needs to be adapted
+//
+// When adding a new feature, be particularly mindful of features that affect function ABIs. Those
+// need to be treated very carefully to avoid introducing unsoundness! This often affects features
+// that enable/disable hardfloat support (see https://github.com/rust-lang/rust/issues/116344 for an
+// example of this going wrong), but features enabling new SIMD registers are also a concern (see
+// https://github.com/rust-lang/rust/issues/116558 for an example of this going wrong).
+//
+// Stabilizing a target feature (setting the 2nd component of the pair to `None`) requires t-lang
+// approval.
 
 const ARM_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
     // tidy-alphabetical-start
diff --git a/compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h b/compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h
index 3f2bf2c9b444d..142384e6d0ca2 100644
--- a/compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h
+++ b/compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h
@@ -25,7 +25,6 @@
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/Scalar.h"
-#include "llvm/Transforms/Vectorize.h"
 
 #define LLVM_VERSION_GE(major, minor)                                          \
   (LLVM_VERSION_MAJOR > (major) ||                                             \
diff --git a/compiler/rustc_metadata/src/lib.rs b/compiler/rustc_metadata/src/lib.rs
index ec2517b581e3e..b06b4fb87cde2 100644
--- a/compiler/rustc_metadata/src/lib.rs
+++ b/compiler/rustc_metadata/src/lib.rs
@@ -8,6 +8,7 @@
 #![cfg_attr(not(bootstrap), feature(coroutines))]
 #![feature(iter_from_coroutine)]
 #![feature(let_chains)]
+#![feature(if_let_guard)]
 #![feature(proc_macro_internals)]
 #![feature(macro_metavar_expr)]
 #![feature(min_specialization)]
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index de436c16ca924..2042863d189db 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -2386,31 +2386,32 @@ pub fn rendered_const<'tcx>(tcx: TyCtxt<'tcx>, body: hir::BodyId) -> String {
         }
     }
 
-    let classification = classify(value);
-
-    if classification == Literal
-        && !value.span.from_expansion()
-        && let Ok(snippet) = tcx.sess.source_map().span_to_snippet(value.span)
-    {
-        // For literals, we avoid invoking the pretty-printer and use the source snippet instead to
-        // preserve certain stylistic choices the user likely made for the sake legibility like
+    match classify(value) {
+        // For non-macro literals, we avoid invoking the pretty-printer and use the source snippet
+        // instead to preserve certain stylistic choices the user likely made for the sake of
+        // legibility, like:
         //
         // * hexadecimal notation
         // * underscores
         // * character escapes
         //
         // FIXME: This passes through `-/*spacer*/0` verbatim.
-        snippet
-    } else if classification == Simple {
+        Literal if !value.span.from_expansion()
+            && let Ok(snippet) = tcx.sess.source_map().span_to_snippet(value.span) => {
+            snippet
+        }
+
         // Otherwise we prefer pretty-printing to get rid of extraneous whitespace, comments and
         // other formatting artifacts.
-        id_to_string(&hir, body.hir_id)
-    } else if tcx.def_kind(hir.body_owner_def_id(body).to_def_id()) == DefKind::AnonConst {
+        Literal | Simple => id_to_string(&hir, body.hir_id),
+
         // FIXME: Omit the curly braces if the enclosing expression is an array literal
         //        with a repeated element (an `ExprKind::Repeat`) as in such case it
         //        would not actually need any disambiguation.
-        "{ _ }".to_owned()
-    } else {
-        "_".to_owned()
+        Complex => if tcx.def_kind(hir.body_owner_def_id(body).to_def_id()) == DefKind::AnonConst {
+            "{ _ }".to_owned()
+        } else {
+            "_".to_owned()
+        }
     }
 }
diff --git a/src/doc/reference b/src/doc/reference
index 16fd3c06d9e55..cd8193e972f61 160000
--- a/src/doc/reference
+++ b/src/doc/reference
@@ -1 +1 @@
-Subproject commit 16fd3c06d9e558dae2d52000818274ae70c9e90a
+Subproject commit cd8193e972f61b92117095fc73b67af767b4d6bc
diff --git a/src/doc/rust-by-example b/src/doc/rust-by-example
index 6709beeb7d0fb..311b84962016b 160000
--- a/src/doc/rust-by-example
+++ b/src/doc/rust-by-example
@@ -1 +1 @@
-Subproject commit 6709beeb7d0fbc5ffc91ac4893a24434123b9bfa
+Subproject commit 311b84962016b28c75525c86e7b3f49fd9101a39
diff --git a/src/doc/rustc-dev-guide b/src/doc/rustc-dev-guide
index b0ee9ec8fa59a..77dbe5782b248 160000
--- a/src/doc/rustc-dev-guide
+++ b/src/doc/rustc-dev-guide
@@ -1 +1 @@
-Subproject commit b0ee9ec8fa59a6c7620165e061f4747202377a62
+Subproject commit 77dbe5782b2488af3bb489ad702eaff438f465bf
diff --git a/tests/rustdoc/issue-115295-macro-const-display.rs b/tests/rustdoc/issue-115295-macro-const-display.rs
new file mode 100644
index 0000000000000..2916c7a84a1ff
--- /dev/null
+++ b/tests/rustdoc/issue-115295-macro-const-display.rs
@@ -0,0 +1,40 @@
+#![crate_name = "foo"]
+
+// @has foo/trait.Trait.html
+pub trait Trait<T> {}
+
+// @has foo/struct.WithConst.html
+pub struct WithConst<const N: usize>;
+
+macro_rules! spans_from_macro {
+    () => {
+        impl WithConst<42> {
+            pub fn new() -> Self {
+                Self
+            }
+        }
+        impl Trait<WithConst<42>> for WithConst<42> {}
+        impl Trait<WithConst<43>> for WithConst<{ 43 }> {}
+        impl Trait<WithConst<{ 44 }>> for WithConst<44> {}
+        pub struct Other {
+            pub field: WithConst<42>,
+        }
+    };
+}
+
+// @has - '//*[@class="impl"]//h3[@class="code-header"]' \
+//     "impl Trait<WithConst<41>> for WithConst<41>"
+impl Trait<WithConst<41>> for WithConst<41> {}
+
+// @has - '//*[@class="impl"]//h3[@class="code-header"]' \
+//     "impl WithConst<42>"
+// @has - '//*[@class="impl"]//h3[@class="code-header"]' \
+//     "impl Trait<WithConst<42>> for WithConst<42>"
+// @has - '//*[@class="impl"]//h3[@class="code-header"]' \
+//     "impl Trait<WithConst<43>> for WithConst<{ 43 }>"
+// @has - '//*[@class="impl"]//h3[@class="code-header"]' \
+//     "impl Trait<WithConst<44>> for WithConst<44>"
+
+// @has foo/struct.Other.html
+// @has - //pre "pub field: WithConst<42>"
+spans_from_macro!();
diff --git a/tests/ui/numbers-arithmetic/saturating-float-casts-wasm.stderr b/tests/ui/numbers-arithmetic/saturating-float-casts-wasm.stderr
new file mode 100644
index 0000000000000..475b41388d3b4
--- /dev/null
+++ b/tests/ui/numbers-arithmetic/saturating-float-casts-wasm.stderr
@@ -0,0 +1,6 @@
+warning: unstable feature specified for `-Ctarget-feature`: `nontrapping-fptoint`
+   |
+   = note: this feature is not stably supported; its behavior can change in the future
+
+warning: 1 warning emitted
+
diff --git a/tests/ui/target-feature/similar-feature-suggestion.stderr b/tests/ui/target-feature/similar-feature-suggestion.stderr
index 2f376065fdfb0..f39dfd401e07c 100644
--- a/tests/ui/target-feature/similar-feature-suggestion.stderr
+++ b/tests/ui/target-feature/similar-feature-suggestion.stderr
@@ -1,6 +1,6 @@
-warning: unknown feature specified for `-Ctarget-feature`: `rdrnd`
+warning: unknown and unstable feature specified for `-Ctarget-feature`: `rdrnd`
    |
-   = note: it is still passed through to the codegen backend
+   = note: it is still passed through to the codegen backend, but use of this feature might be unsound and the behavior of this feature can change in the future
    = help: you might have meant: `rdrand`
 
 warning: 1 warning emitted
diff --git a/tests/ui/target-feature/unstable-feature.rs b/tests/ui/target-feature/unstable-feature.rs
new file mode 100644
index 0000000000000..bd0d72938f4da
--- /dev/null
+++ b/tests/ui/target-feature/unstable-feature.rs
@@ -0,0 +1,6 @@
+// compile-flags: -Ctarget-feature=+vaes --crate-type=rlib --target=x86_64-unknown-linux-gnu
+// build-pass
+// needs-llvm-components: x86
+
+#![feature(no_core)]
+#![no_core]
diff --git a/tests/ui/target-feature/unstable-feature.stderr b/tests/ui/target-feature/unstable-feature.stderr
new file mode 100644
index 0000000000000..d34544c5c2773
--- /dev/null
+++ b/tests/ui/target-feature/unstable-feature.stderr
@@ -0,0 +1,6 @@
+warning: unstable feature specified for `-Ctarget-feature`: `vaes`
+   |
+   = note: this feature is not stably supported; its behavior can change in the future
+
+warning: 1 warning emitted
+