6 files changed, 20 insertions, 0 deletions
diff --git a/compiler/rustc/Cargo.toml b/compiler/rustc/Cargo.toml
index 5008069542f..a2fc9d5c408 100644
--- a/compiler/rustc/Cargo.toml
+++ b/compiler/rustc/Cargo.toml
@@ -30,5 +30,6 @@ features = ['unprefixed_malloc_on_supported_platforms']
 jemalloc = ['dep:jemalloc-sys']
 llvm = ['rustc_driver_impl/llvm']
 max_level_info = ['rustc_driver_impl/max_level_info']
+rustc_randomized_layouts = ['rustc_driver_impl/rustc_randomized_layouts']
 rustc_use_parallel_compiler = ['rustc_driver_impl/rustc_use_parallel_compiler']
 # tidy-alphabetical-end
diff --git a/compiler/rustc_driver_impl/Cargo.toml b/compiler/rustc_driver_impl/Cargo.toml
index 91cbffcd707..6d6d3f35a4b 100644
--- a/compiler/rustc_driver_impl/Cargo.toml
+++ b/compiler/rustc_driver_impl/Cargo.toml
@@ -23,6 +23,7 @@ rustc_hir_analysis = { path = "../rustc_hir_analysis" }
 rustc_hir_pretty = { path = "../rustc_hir_pretty" }
 rustc_hir_typeck = { path = "../rustc_hir_typeck" }
 rustc_incremental = { path = "../rustc_incremental" }
+rustc_index = { path = "../rustc_index" }
 rustc_infer = { path = "../rustc_infer" }
 rustc_interface = { path = "../rustc_interface" }
 rustc_lint = { path = "../rustc_lint" }
@@ -72,6 +73,10 @@ ctrlc = "3.4.4"
 # tidy-alphabetical-start
 llvm = ['rustc_interface/llvm']
 max_level_info = ['rustc_log/max_level_info']
+rustc_randomized_layouts = [
+    'rustc_index/rustc_randomized_layouts',
+    'rustc_middle/rustc_randomized_layouts'
+]
 rustc_use_parallel_compiler = [
     'rustc_data_structures/rustc_use_parallel_compiler',
     'rustc_interface/rustc_use_parallel_compiler',
diff --git a/compiler/rustc_index/Cargo.toml b/compiler/rustc_index/Cargo.toml
index 92ea3f278dc..f7d18f84e34 100644
--- a/compiler/rustc_index/Cargo.toml
+++ b/compiler/rustc_index/Cargo.toml
@@ -20,4 +20,5 @@ nightly = [
     "dep:rustc_macros",
     "rustc_index_macros/nightly",
 ]
+rustc_randomized_layouts = []
 # tidy-alphabetical-end
diff --git a/compiler/rustc_index/src/lib.rs b/compiler/rustc_index/src/lib.rs
index f773b5b46ad..52f354b8eca 100644
--- a/compiler/rustc_index/src/lib.rs
+++ b/compiler/rustc_index/src/lib.rs
@@ -33,8 +33,19 @@ pub use vec::IndexVec;
 ///
 /// </div>
 #[macro_export]
+#[cfg(not(feature = "rustc_randomized_layouts"))]
 macro_rules! static_assert_size {
     ($ty:ty, $size:expr) => {
         const _: [(); $size] = [(); ::std::mem::size_of::<$ty>()];
     };
 }
+
+#[macro_export]
+#[cfg(feature = "rustc_randomized_layouts")]
+macro_rules! static_assert_size {
+    ($ty:ty, $size:expr) => {
+        // no effect other than using the statements.
+        // struct sizes are not deterministic under randomized layouts
+        const _: (usize, usize) = ($size, ::std::mem::size_of::<$ty>());
+    };
+}
diff --git a/compiler/rustc_middle/Cargo.toml b/compiler/rustc_middle/Cargo.toml
index 69e3b703cce..b23589afb58 100644
--- a/compiler/rustc_middle/Cargo.toml
+++ b/compiler/rustc_middle/Cargo.toml
@@ -40,5 +40,6 @@ tracing = "0.1"
 
 [features]
 # tidy-alphabetical-start
+rustc_randomized_layouts = []
 rustc_use_parallel_compiler = ["dep:rustc-rayon-core"]
 # tidy-alphabetical-end
diff --git a/compiler/rustc_middle/src/query/plumbing.rs b/compiler/rustc_middle/src/query/plumbing.rs
index c9bd702cce3..0320a91d142 100644
--- a/compiler/rustc_middle/src/query/plumbing.rs
+++ b/compiler/rustc_middle/src/query/plumbing.rs
@@ -337,6 +337,7 @@ macro_rules! define_callbacks {
                 // Ensure that values grow no larger than 64 bytes by accident.
                 // Increase this limit if necessary, but do try to keep the size low if possible
                 #[cfg(target_pointer_width = "64")]
+                #[cfg(not(feature = "rustc_randomized_layouts"))]
                 const _: () = {
                     if mem::size_of::<Value<'static>>() > 64 {
                         panic!("{}", concat!(