Could a gatekeeper review the attached patch? It fixes some AMD64 ABI
compatibility problems and also eliminates some unnecessary struct
copies. The second part should apply to all targets.
Here is the proposed log message:
Improve AMD64 ABI compliance and avoid unnecessary struct copies.
For the following code, the compiler generated unnecessary struct copies
for a return value that has a size too big to be passed in registers.
typedef struct { char big[1024]; } C;
C gc;
extern C bar9 (void);
extern C check9 (void) { return bar9 (); }
In this case there were two copies and one temporary variable generated.
After this change the compiler does not generate any extra copies.
According to the AMD64 ABI, the caller provides space for the return
value in a hidden first argument and this address is returned in %rax.
Previously the compiler was not following this rule.
The change handles the similar cases of initialization by function
call ("C c = bar9();") and assignment to a pointer ("*cp = bar9()").
Also, a complex long double field is now returned in the register pair
(%st0, %st1) as specified by the AMD64 ABI.
I am still looking for a review for the patch I posted last week (May
10) as well. Thanks,
-David Coakley / AMD Open Source Compiler Engineering
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