Fix ARM and AArch64 calling convention for passing small composite types

On big-endian the values need to be right-aligned within a 64-bit register, as if the value had been read with a 64-bit load instruction.

Author: Amanieu d'Antras

compiler/rustc_target/src/abi/call/aarch64.rs

@@ -40,17 +40,7 @@ where
     let size = ret.layout.size;
     let bits = size.bits();
     if bits <= 128 {
-        let unit = if bits <= 8 {
-            Reg::i8()
-        } else if bits <= 16 {
-            Reg::i16()
-        } else if bits <= 32 {
-            Reg::i32()
-        } else {
-            Reg::i64()
-        };
-
-        ret.cast_to(Uniform { unit, total: size });
+        ret.cast_to(Uniform { unit: Reg::i64(), total: size });
         return;
     }
     ret.make_indirect();
@@ -72,17 +62,7 @@ where
     let size = arg.layout.size;
     let bits = size.bits();
     if bits <= 128 {
-        let unit = if bits <= 8 {
-            Reg::i8()
-        } else if bits <= 16 {
-            Reg::i16()
-        } else if bits <= 32 {
-            Reg::i32()
-        } else {
-            Reg::i64()
-        };
-
-        arg.cast_to(Uniform { unit, total: size });
+        arg.cast_to(Uniform { unit: Reg::i64(), total: size });
         return;
     }
     arg.make_indirect();

compiler/rustc_target/src/abi/call/arm.rs

@@ -45,14 +45,7 @@ where
     let size = ret.layout.size;
     let bits = size.bits();
     if bits <= 32 {
-        let unit = if bits <= 8 {
-            Reg::i8()
-        } else if bits <= 16 {
-            Reg::i16()
-        } else {
-            Reg::i32()
-        };
-        ret.cast_to(Uniform { unit, total: size });
+        ret.cast_to(Uniform { unit: Reg::i32(), total: size });
         return;
     }
     ret.make_indirect();