Inferred return value location does not update when changing return type of function

[bdash]

Version and Platform (required):

• Binary Ninja Version: 5.4.9744-dev Ultimate, d7f134fd
• OS: macos 26.5.0
• CPU Architecture: arm64

Bug Description:
When changing a function of type int64_t GetPoint() __pure to have a return type of struct Point, the return value location remains fixed at __location("x0"), despite Point being too large to fit within x0. Since the return value location was originally inferred by analysis, updating the return type should cause it to be recomputed.

Steps To Reproduce:

1. Open libtest.dylib from the attached zip file.
2. Observe that GetPoint looks like so:

Disassembly	HLIL
004002d0 int64_t GetPoint() __pure 004002d0 0 20078652 mov w0, #0x3039 004002d4 0 41268152 mov w1, #0x932 004002d8 0 2100a072 movk w1, #0x1, lsl #0x10 {0x10932} 004002dc 0 c0035fd6 ret	004002d0 int64_t GetPoint() __pure 004002dc return 0x3039

3. Define a type struct Point { uint64_t x, y; };.
4. Change the return type of GetPoint to Point.
5. GetPoint updates to look like so. Note the explicit __location("x0") override:

Disassembly	HLIL
004002d0 struct Point GetPoint() __location("x0") __pure 004002d0 0 20078652 mov w0, #0x3039 004002d4 0 41268152 mov w1, #0x932 004002d8 0 2100a072 movk w1, #0x1, lsl #0x10 {0x10932} 004002dc 0 c0035fd6 ret	004002d0 struct Point GetPoint() __location("x0") __pure 004002dc return 0x3039

6. Use Edit Function Properties to change the return value's "source" from Custom to Default. Note that the location column updates to x1:x0 when doing this.
7. GetPoint has now updated to have the expected HLIL:

Disassembly	HLIL
004002d0 struct Point GetPoint() __pure 004002d0 0 20078652 mov w0, #0x3039 004002d4 0 41268152 mov w1, #0x932 004002d8 0 2100a072 movk w1, #0x1, lsl #0x10 {0x10932} 004002dc 0 c0035fd6 ret	004002d0 struct Point GetPoint() __pure 004002d0 struct Point result 004002d0 result.x = 0x3039 004002d0 result.y = 0x10932 004002dc return result

Expected Behavior:
Changing the type in step 4 should be sufficient to update the return value location. It should not be necessary to explicitly reset the return value's "source" to Default since the user never explicitly changed it from Default.

Binary:
libtest.dylib.zip

Created via:

mrowe@quicksilver:~$ cat test.cpp
#include <stdint.h>

struct Point {
    uint64_t x;
    uint64_t y;
};

Point GetPoint()
{
    return { 12345, 67890 };
}

mrowe@quicksilver:~$ cc -Os -shared -o libtest.dylib test.cpp
mrowe@quicksilver:~$