Add assembly test for -Zreg-struct-return option

tests/assembly-llvm/reg-struct-return.rs

@@ -0,0 +1,144 @@
+//! Tests that -Zreg-struct-return changes ABI for small struct returns
+//! from hidden-pointer convention to register-return on x86_32.
+//! This test covers:
+//! * Direct struct construction, verifying register return versus hidden pointer
+//! * External function calls returning structs, verifying ABI mismatch handling
+//@ add-core-stubs
+//@ assembly-output: emit-asm
+//@ compile-flags: -O --target=i686-unknown-linux-gnu -Crelocation-model=static
+//@ revisions: WITH WITHOUT
+//@[WITH] compile-flags: -Zreg-struct-return
+//@ needs-llvm-components: x86
+
+#![feature(no_core)]
+#![no_std]
+#![no_core]
+#![crate_type = "lib"]
+
+extern crate minicore;
+use minicore::*;
+
+// Verifies ABI changes for small struct, where both fields fit into one register.
+// WITH is expected to use register return, WITHOUT should use hidden pointer.
+mod small {
+    struct small_t {
+        a: i8,
+        b: i8,
+    }
+
+    unsafe extern "C" {
+        fn small() -> small_t;
+    }
+
+    #[unsafe(no_mangle)]
+    pub unsafe extern "C" fn small_direct_construction() -> small_t {
+        // (42 << 8) | 42 = 10794
+
+        // WITH-LABEL: small_direct_construction
+        // WITH: movw $10794, %ax
+        // WITH: retl
+
+        // WITHOUT-LABEL: small_direct_construction
+        // WITHOUT: movl 4(%esp), %e{{.*}}
+        // WITHOUT: movw $10794, (%e{{.*}})
+        // WITHOUT: retl $4
+        small_t { a: 42, b: 42 }
+    }
+
+    #[unsafe(no_mangle)]
+    pub unsafe extern "C" fn small_call() -> small_t {
+        // WITH-LABEL: small_call
+        // WITH: jmp small
+
+        // WITHOUT-LABEL: small_call
+        // WITHOUT: calll small
+        // WITHOUT: retl $4
+        small()
+    }
+}
+
+// Verifies ABI changes for a struct of size 8, which is the maximum size
+// for reg-struct-return.
+// WITH is expected to still use register return, WITHOUT should use hidden
+// pointer.
+mod pivot {
+    struct pivot_t {
+        a: i32,
+        b: i32,
+    }
+
+    unsafe extern "C" {
+        fn pivot() -> pivot_t;
+    }
+
+    #[unsafe(no_mangle)]
+    pub unsafe extern "C" fn pivot_direct_construction() -> pivot_t {
+        // WITH-LABEL: pivot_direct_construction
+        // WITH: movl $42, %e{{.*}}
+        // WITH: movl $42, %e{{.*}}
+        // WITH: retl
+
+        // WITHOUT-LABEL: pivot_direct_construction
+        // WITHOUT: movl 4(%esp), %e{{.*}}
+        // WITHOUT: movl $42, (%e{{.*}})
+        // WITHOUT: movl $42, 4(%e{{.*}})
+        // WITHOUT: retl $4
+        pivot_t { a: 42, b: 42 }
+    }
+
+    #[unsafe(no_mangle)]
+    pub unsafe extern "C" fn pivot_call() -> pivot_t {
+        // WITH-LABEL: pivot_call
+        // WITH: jmp pivot
+
+        // WITHOUT-LABEL: pivot_call
+        // WITHOUT: calll pivot
+        // WITHOUT: retl $4
+        pivot()
+    }
+}
+
+// Verifies ABI changes for a struct of size 12, which is larger than the
+// maximum size for reg-struct-return (8 bytes).
+// Here, both WITH and WITHOUT should use the hidden pointer convention.
+mod large {
+    struct large_t {
+        a: i32,
+        b: i32,
+        c: i32,
+    }
+
+    unsafe extern "C" {
+        fn large() -> large_t;
+    }
+
+    #[unsafe(no_mangle)]
+    pub unsafe extern "C" fn large_direct_construction() -> large_t {
+        // WITH-LABEL: large_direct_construction
+        // WITH: movl 4(%esp), %e{{.*}}
+        // WITH: movl $42, (%e{{.*}})
+        // WITH: movl $42, 4(%e{{.*}})
+        // WITH: movl $42, 8(%e{{.*}})
+        // WITH: retl $4
+
+        // WITHOUT-LABEL: large_direct_construction
+        // WITHOUT: movl 4(%esp), %e{{.*}}
+        // WITHOUT: movl $42, (%e{{.*}})
+        // WITHOUT: movl $42, 4(%e{{.*}})
+        // WITHOUT: movl $42, 8(%e{{.*}})
+        // WITHOUT: retl $4
+        large_t { a: 42, b: 42, c: 42 }
+    }
+
+    #[unsafe(no_mangle)]
+    pub unsafe extern "C" fn large_call() -> large_t {
+        // WITH-LABEL: large_call
+        // WITH: calll large
+        // WITH: retl $4
+
+        // WITHOUT-LABEL: large_call
+        // WITHOUT: calll large
+        // WITHOUT: retl $4
+        large()
+    }
+}