LLVM 18 x86 data layout update

With https://reviews.llvm.org/D86310 LLVM now has i128 aligned to
16-bytes on x86 based platforms. This will be in LLVM-18. This patch
updates all our spec targets to be 16-byte aligned, and removes the
alignment when speaking to older LLVM.

This results in Rust overaligning things relative to LLVM on older LLVMs.

This alignment change was discussed in rust-lang/compiler-team#683

See #54341 for additional information about why this is happening and
where this will be useful in the future.

This *does not* stabilize `i128`/`u128` for FFI.

Author: maurer

compiler/rustc_ast/src/ast.rs

@@ -3238,9 +3238,13 @@ mod size_asserts {
     static_assert_size!(Impl, 136);
     static_assert_size!(Item, 136);
     static_assert_size!(ItemKind, 64);
-    static_assert_size!(LitKind, 24);
+    // This can be removed after i128:128 is in the bootstrap compiler's target.
+    #[cfg(not(bootstrap))]
+    static_assert_size!(LitKind, 32);
     static_assert_size!(Local, 72);
-    static_assert_size!(MetaItemLit, 40);
+    // This can be removed after i128:128 is in the bootstrap compiler's target.
+    #[cfg(not(bootstrap))]
+    static_assert_size!(MetaItemLit, 48);
     static_assert_size!(Param, 40);
     static_assert_size!(Pat, 72);
     static_assert_size!(Path, 24);

compiler/rustc_codegen_llvm/src/context.rs

@@ -145,6 +145,14 @@ pub unsafe fn create_module<'ll>(
                 .replace("-Fi64", "");
         }
     }
+    if llvm_version < (18, 0, 0) {
+        if sess.target.arch == "x86" || sess.target.arch == "x86_64" {
+            // LLVM 18 adjusts i128 to be 128-bit aligned on x86 variants.
+            // Earlier LLVMs leave this as default alignment, so remove it.
+            // See https://reviews.llvm.org/D86310
+            target_data_layout = target_data_layout.replace("-i128:128", "");
+        }
+    }
 
     // Ensure the data-layout values hardcoded remain the defaults.
     if sess.target.is_builtin {

compiler/rustc_middle/src/mir/mod.rs

@@ -1651,13 +1651,19 @@ mod size_asserts {
     use super::*;
     use rustc_data_structures::static_assert_size;
     // tidy-alphabetical-start
-    static_assert_size!(BasicBlockData<'_>, 136);
+    // This can be removed after i128:128 is in the bootstrap compiler's target.
+    #[cfg(not(bootstrap))]
+    static_assert_size!(BasicBlockData<'_>, 144);
     static_assert_size!(LocalDecl<'_>, 40);
     static_assert_size!(SourceScopeData<'_>, 72);
     static_assert_size!(Statement<'_>, 32);
     static_assert_size!(StatementKind<'_>, 16);
-    static_assert_size!(Terminator<'_>, 104);
-    static_assert_size!(TerminatorKind<'_>, 88);
+    // This can be removed after i128:128 is in the bootstrap compiler's target.
+    #[cfg(not(bootstrap))]
+    static_assert_size!(Terminator<'_>, 112);
+    // This can be removed after i128:128 is in the bootstrap compiler's target.
+    #[cfg(not(bootstrap))]
+    static_assert_size!(TerminatorKind<'_>, 96);
     static_assert_size!(VarDebugInfo<'_>, 88);
     // tidy-alphabetical-end
 }

compiler/rustc_target/src/spec/targets/i386_apple_ios.rs

@@ -11,7 +11,7 @@ pub fn target() -> Target {
         llvm_target: ios_sim_llvm_target(arch).into(),
         pointer_width: 32,
         data_layout: "e-m:o-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
-            f64:32:64-f80:128-n8:16:32-S128"
+            i128:128-f64:32:64-f80:128-n8:16:32-S128"
             .into(),
         arch: arch.target_arch(),
         options: TargetOptions { max_atomic_width: Some(64), ..opts("ios", arch) },

compiler/rustc_target/src/spec/targets/i686_apple_darwin.rs

@@ -18,7 +18,7 @@ pub fn target() -> Target {
         llvm_target: macos_llvm_target(Arch::I686).into(),
         pointer_width: 32,
         data_layout: "e-m:o-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
-            f64:32:64-f80:128-n8:16:32-S128"
+            i128:128-f64:32:64-f80:128-n8:16:32-S128"
             .into(),
         arch: arch.target_arch(),
         options: TargetOptions { mcount: "\u{1}mcount".into(), ..base },

compiler/rustc_target/src/spec/targets/i686_linux_android.rs

@@ -17,7 +17,7 @@ pub fn target() -> Target {
         llvm_target: "i686-linux-android".into(),
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
-            f64:32:64-f80:32-n8:16:32-S128"
+            i128:128-f64:32:64-f80:32-n8:16:32-S128"
             .into(),
         arch: "x86".into(),
         options: TargetOptions { supported_sanitizers: SanitizerSet::ADDRESS, ..base },

compiler/rustc_target/src/spec/targets/i686_pc_windows_gnu.rs

@@ -19,7 +19,7 @@ pub fn target() -> Target {
         llvm_target: "i686-pc-windows-gnu".into(),
         pointer_width: 32,
         data_layout: "e-m:x-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
-            i64:64-f80:32-n8:16:32-a:0:32-S32"
+            i64:64-i128:128-f80:32-n8:16:32-a:0:32-S32"
             .into(),
         arch: "x86".into(),
         options: base,

compiler/rustc_target/src/spec/targets/i686_pc_windows_gnullvm.rs

@@ -18,7 +18,7 @@ pub fn target() -> Target {
         llvm_target: "i686-pc-windows-gnu".into(),
         pointer_width: 32,
         data_layout: "e-m:x-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
-            i64:64-f80:32-n8:16:32-a:0:32-S32"
+            i64:64-i128:128-f80:32-n8:16:32-a:0:32-S32"
             .into(),
         arch: "x86".into(),
         options: base,

compiler/rustc_target/src/spec/targets/i686_pc_windows_msvc.rs

@@ -24,7 +24,7 @@ pub fn target() -> Target {
         llvm_target: "i686-pc-windows-msvc".into(),
         pointer_width: 32,
         data_layout: "e-m:x-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
-            i64:64-f80:128-n8:16:32-a:0:32-S32"
+            i64:64-i128:128-f80:128-n8:16:32-a:0:32-S32"
             .into(),
         arch: "x86".into(),
         options: base,

compiler/rustc_target/src/spec/targets/i686_unknown_freebsd.rs

@@ -11,7 +11,7 @@ pub fn target() -> Target {
         llvm_target: "i686-unknown-freebsd".into(),
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
-            f64:32:64-f80:32-n8:16:32-S128"
+            i128:128-f64:32:64-f80:32-n8:16:32-S128"
             .into(),
         arch: "x86".into(),
         options: base,