Rollup merge of #130777 - azhogin:azhogin/reg-struct-return, r=workingjubilee

rust_for_linux: -Zreg-struct-return commandline flag for X86 (#116973)

Command line flag `-Zreg-struct-return` for X86 (32-bit) for rust-for-linux.
This flag enables the same behavior as the `abi_return_struct_as_int` target spec key.

- Tracking issue: https://github.com/rust-lang/rust/issues/116973

3 files changed, 12 insertions, 0 deletions

diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index 736a5ce0704..6c26a781487 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -490,6 +490,10 @@ pub(crate) struct UnsupportedRegparm {
 pub(crate) struct UnsupportedRegparmArch;
 
 #[derive(Diagnostic)]
+#[diag(session_unsupported_reg_struct_return_arch)]
+pub(crate) struct UnsupportedRegStructReturnArch;
+
+#[derive(Diagnostic)]
 #[diag(session_failed_to_create_profiler)]
 pub(crate) struct FailedToCreateProfiler {
     pub(crate) err: String,
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 2c0302bbb2b..fea37904914 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1988,6 +1988,9 @@ options! {
         "enable queries of the dependency graph for regression testing (default: no)"),
     randomize_layout: bool = (false, parse_bool, [TRACKED],
         "randomize the layout of types (default: no)"),
+    reg_struct_return: bool = (false, parse_bool, [TRACKED],
+        "On x86-32 targets, it overrides the default ABI to return small structs in registers.
+        It is UNSOUND to link together crates that use different values for this flag!"),
     regparm: Option<u32> = (None, parse_opt_number, [TRACKED],
         "On x86-32 targets, setting this to N causes the compiler to pass N arguments \
         in registers EAX, EDX, and ECX instead of on the stack for\
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 120ae9946ea..7db3b7b7d9d 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -1305,6 +1305,11 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
             sess.dcx().emit_err(errors::UnsupportedRegparmArch);
         }
     }
+    if sess.opts.unstable_opts.reg_struct_return {
+        if sess.target.arch != "x86" {
+            sess.dcx().emit_err(errors::UnsupportedRegStructReturnArch);
+        }
+    }
 
     // The code model check applies to `thunk` and `thunk-extern`, but not `thunk-inline`, so it is
     // kept as a `match` to force a change if new ones are added, even if we currently only support