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 ignores the
alignment change when checking what the LLVM's default spec is on
the relevant targets for older LLVMs.

* This is a potentially breaking change, as u128 and i128 will have
  their alignment increase on some platforms.
* This results in Rust overaligning things relative to LLVM on older
  LLVMs.

See #54341

Author: maurer

compiler/rustc_ast/src/ast.rs

@@ -3185,9 +3185,13 @@ 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

@@ -186,12 +186,26 @@ pub unsafe fn create_module<'ll>(
         let cfg_llvm_root = option_env!("CFG_LLVM_ROOT").unwrap_or("");
         let custom_llvm_used = !cfg_llvm_root.trim().is_empty();
 
-        if !custom_llvm_used && target_data_layout != llvm_data_layout {
+        let mut checked_target_data_layout = target_data_layout.clone();
+        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.
+                // We only modify the checked data layout because LLVM will generate incorrect code without it.
+                // This matches the behavior of Clang on earlier LLVMs, which reduces the likelihood of problems arising from it.
+                // This removal acts as our acknowledgement of this deviation between the default LLVM target spec and the one we are using.
+                //
+                // See https://reviews.llvm.org/D86310
+                checked_target_data_layout = checked_target_data_layout.replace("-i128:128", "");
+            }
+        }
+
+        if !custom_llvm_used && checked_target_data_layout != llvm_data_layout {
             bug!(
                 "data-layout for target `{rustc_target}`, `{rustc_layout}`, \
                   differs from LLVM target's `{llvm_target}` default layout, `{llvm_layout}`",
                 rustc_target = sess.opts.target_triple,
-                rustc_layout = target_data_layout,
+                rustc_layout = checked_target_data_layout,
                 llvm_target = sess.target.llvm_target,
                 llvm_layout = llvm_data_layout
             );

compiler/rustc_middle/src/mir/mod.rs

@@ -1585,13 +1585,19 @@ 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/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 {

compiler/rustc_target/src/spec/i686_apple_darwin.rs

@@ -19,7 +19,7 @@ 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/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/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,

compiler/rustc_target/src/spec/i686_unknown_haiku.rs

@@ -11,7 +11,7 @@ pub fn target() -> Target {
         llvm_target: "i686-unknown-haiku".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,

compiler/rustc_target/src/spec/i686_unknown_hurd_gnu.rs

@@ -11,7 +11,7 @@ pub fn target() -> Target {
         llvm_target: "i686-unknown-hurd-gnu".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,

compiler/rustc_target/src/spec/i686_unknown_linux_gnu.rs

@@ -12,7 +12,7 @@ pub fn target() -> Target {
         llvm_target: "i686-unknown-linux-gnu".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,