Fix oversized loads on x86_64 SysV FFI calls

The x86_64 SysV ABI should use exact sizes for small structs passed in
registers, i.e. a struct that occupies 3 bytes should use an i24,
instead of the i32 it currently uses.

Refs #45543

src/librustc_trans/cabi_x86_64.rs

@@ -134,12 +134,13 @@ fn reg_component(cls: &[Option<Class>], i: &mut usize, size: Size) -> Option<Reg
         None => None,
         Some(Class::Int) => {
             *i += 1;
-            Some(match size.bytes() {
-                1 => Reg::i8(),
-                2 => Reg::i16(),
-                3 |
-                4 => Reg::i32(),
-                _ => Reg::i64()
+            Some(if size.bytes() < 8 {
+                Reg {
+                    kind: RegKind::Integer,
+                    size
+                }
+            } else {
+                Reg::i64()
             })
         }
         Some(Class::Sse) => {

src/test/codegen/abi-x86_64_sysv.rs

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// only-x86_64
+
+// compile-flags: -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+
+pub struct S24 {
+  a: i8,
+  b: i8,
+  c: i8,
+}
+
+pub struct S48 {
+  a: i16,
+  b: i16,
+  c: i8,
+}
+
+// CHECK: i24 @struct_24_bits(i24
+#[no_mangle]
+pub extern "sysv64" fn struct_24_bits(a: S24) -> S24 {
+  a
+}
+
+// CHECK: i48 @struct_48_bits(i48
+#[no_mangle]
+pub extern "sysv64" fn struct_48_bits(a: S48) -> S48 {
+  a
+}

src/test/codegen/repr-transparent-sysv64.rs

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// only-x86_64
+
+// compile-flags: -C no-prepopulate-passes
+
+#![crate_type="lib"]
+#![feature(repr_transparent)]
+
+#[repr(C)]
+pub struct Rgb8 { r: u8, g: u8, b: u8 }
+
+#[repr(transparent)]
+pub struct Rgb8Wrap(Rgb8);
+
+// CHECK: i24 @test_Rgb8Wrap(i24)
+#[no_mangle]
+pub extern "sysv64" fn test_Rgb8Wrap(_: Rgb8Wrap) -> Rgb8Wrap { loop {} }
+
+#[repr(C)]
+pub union FloatBits {
+    float: f32,
+    bits: u32,
+}
+
+#[repr(transparent)]
+pub struct SmallUnion(FloatBits);
+
+// CHECK: i32 @test_SmallUnion(i32)
+#[no_mangle]
+pub extern "sysv64" fn test_SmallUnion(_: SmallUnion) -> SmallUnion { loop {} }

src/test/codegen/repr-transparent.rs

@@ -123,55 +123,13 @@ pub struct UnitPhantom<T, U> { val: T, unit: PhantomData<U> }
 pub extern fn test_Projection(_: StructWithProjection) -> StructWithProjection { loop {} }
 
 
-// The rest of this file tests newtypes around small aggregates on an ABI where small aggregates are
-// packed into one register. This is ABI-dependent, so instead we focus on one ABI and supply a
-// dummy definition for other ABIs to keep FileCheck happy.
+// All that remains to be tested are aggregates. They are tested in separate files called repr-
+// transparent-*.rs  with `only-*` or `ignore-*` directives, because the expected LLVM IR
+// function signatures vary so much that it's not reasonably possible to cover all of them with a
+// single CHECK line.
 //
-// Bigger aggregates are tested in separate files called repr-transparent-aggregate-*.rs because
-// there, the expected LLVM IR function signatures vary so much that it's not reasonably possible to
-// cover all of them with a single CHECK line. Instead we group ABIs by the general "shape" of the
-// signature and have a separate test file for each bin.
-//
-// PS: You may be wondering why we don't just compare the return types and argument types for
-// equality with FileCheck regex captures. Well, rustc doesn't perform newtype unwrapping on
-// newtypes containing aggregates. This is OK on all ABIs we support, but because LLVM has not
-// gotten rid of pointee types yet, the IR function signature will be syntactically different (%Foo*
-// vs %FooWrapper*).
-
-#[repr(C)]
-pub struct Rgb8 { r: u8, g: u8, b: u8 }
-
-#[repr(transparent)]
-pub struct Rgb8Wrap(Rgb8);
-
-// NB: closing parenthesis is missing because sometimes the argument has a name and sometimes not
-// CHECK: define i32 @test_Rgb8Wrap(i32
-#[no_mangle]
-#[cfg(all(target_arch="x86_64", target_os="linux"))]
-pub extern fn test_Rgb8Wrap(_: Rgb8Wrap) -> Rgb8Wrap { loop {} }
-
-#[cfg(not(all(target_arch="x86_64", target_os="linux")))]
-#[no_mangle]
-pub extern fn test_Rgb8Wrap(_: u32) -> u32 { loop {} }
-
-// Same as with the small struct above: ABI-dependent, we only test the interesting case
-// (ABIs that pack the aggregate into a scalar) and stub it out on other ABIs
-
-#[repr(C)]
-pub union FloatBits {
-    float: f32,
-    bits: u32,
-}
-
-#[repr(transparent)]
-pub struct SmallUnion(FloatBits);
-
-// NB: closing parenthesis is missing because sometimes the argument has a name and sometimes not
-// CHECK: define i32 @test_SmallUnion(i32
-#[no_mangle]
-#[cfg(all(target_arch="x86_64", target_os="linux"))]
-pub extern fn test_SmallUnion(_: SmallUnion) -> SmallUnion { loop {} }
-
-#[cfg(not(all(target_arch="x86_64", target_os="linux")))]
-#[no_mangle]
-pub extern fn test_SmallUnion(_: u32) -> u32 { loop {} }
+// You may be wondering why we don't just compare the return types and argument types for equality
+// with FileCheck regex captures. Well, rustc doesn't perform newtype unwrapping on newtypes
+// containing aggregates. This is OK on all ABIs we support, but because LLVM has not gotten rid of
+// pointee types yet, the IR function signature will be syntactically different (%Foo* vs
+// %FooWrapper*).