Auto merge of rust-lang#137365 - workingjubilee:deconditionalize-aarch64-abi-code, r=<try>

compiler: Make extension of `{i,u}{8,16}` unconditional for AAPCS

r? `@ghost`

Testing a hypothesis...

try-job: aarch64-apple
try-job: aarch64-gnu
try-job: aarch64-gnu-debug
try-job: dist-aarch64-android
try-job: dist-aarch64-apple
try-job: dist-aarch64-linux
try-job: dist-aarch64-msvc

Author: bors

compiler/rustc_target/src/callconv/aarch64.rs

@@ -83,12 +83,10 @@ where
         return;
     }
     if !ret.layout.is_aggregate() {
-        if kind == AbiKind::DarwinPCS {
-            // On Darwin, when returning an i8/i16, it must be sign-extended to 32 bits,
-            // and likewise a u8/u16 must be zero-extended to 32-bits.
-            // See also: <https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Pass-Arguments-to-Functions-Correctly>
-            ret.extend_integer_width_to(32)
-        }
+        // Even if AAPCS does not demand sign extension of smaller-than-32-bit integer returns,
+        // Darwin requires it: <https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Pass-Arguments-to-Functions-Correctly>
+        // It is harmless to do so in every case. If you ask for only 16 bits, don't inspect the other 48!
+        ret.extend_integer_width_to(32);
         softfloat_float_abi(cx.target_spec(), ret);
         return;
     }
@@ -115,14 +113,11 @@ where
         return;
     }
     if !arg.layout.is_aggregate() {
-        if kind == AbiKind::DarwinPCS {
-            // On Darwin, when passing an i8/i16, it must be sign-extended to 32 bits,
-            // and likewise a u8/u16 must be zero-extended to 32-bits.
-            // See also: <https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Pass-Arguments-to-Functions-Correctly>
-            arg.extend_integer_width_to(32);
-        }
+        // Even if AAPCS does not demand sign extension of smaller-than-32-bit integer arguments,
+        // Darwin requires it: <https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Pass-Arguments-to-Functions-Correctly>
+        // It is harmless to do so in every case. If you ask for only 16 bits, don't inspect the other 48!
+        arg.extend_integer_width_to(32);
         softfloat_float_abi(cx.target_spec(), arg);
-
         return;
     }
     if let Some(uniform) = is_homogeneous_aggregate(cx, arg) {