> On Dec 8, 2016, at 9:27 AM, Kurt Kennett <kurt.kenn...@microsoft.com> wrote:
>
> This seems kind of silly.
> Why isn't this just const data? This adds code and memory accesses that are
> worthless and happen on every call to the function.
>
K2,
I think this is an attempt to conform to the coding standard?
I do agree it is pointless to make it static if you are going to initialize it
every time. Seems like it would have been better to make this a global
variable.
Given that a static local variable is very much like a global that is limited
in scope it may make sense to relax the coding standard in this regard (I did
not re-read the coding standard so hopefully this is not a bad assumption), or
just require pre-initialized local static variables to be globals?
In this simple example you can see that a local static variable that is
initialized ends up with code generation that is very close to a global
variable. The name is not global and it is mangled with the function name. The
other interesting tidbit is the compiler realized the static was const and
marked it as such.
~/work/Compiler>cat static.c
const unsigned char gMonthDays[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31,
30, 131 };
int test (int i)
{
static unsigned char MonthDays[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31,
30, 31 };
return MonthDays[i];
}
~/work/Compiler>clang -S -Os static.c
~/work/Compiler>cat static.S
.section __TEXT,__text,regular,pure_instructions
.globl _test
_test: ## @test
pushq %rbp
movq %rsp, %rbp
movslq %edi, %rax
leaq _test.MonthDays(%rip), %rcx
movzbl (%rax,%rcx), %eax
popq %rbp
retq
.section __TEXT,__const
.globl _gMonthDays ## @gMonthDays
_gMonthDays:
.ascii "\037\034\037\036\037\036\037\037\036\037\036\203"
_test.MonthDays: ## @test.MonthDays
.ascii "\037\034\037\036\037\036\037\037\036\037\036\037"
Note: I had to make gMonthDays different than _test.MonthDays or
_test.MonthDays gets optimized out.
Thanks,
Andrew Fish
> K2
>
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of Dandan
> Bi
> Sent: Thursday, December 8, 2016 2:54 AM
> To: edk2-devel@lists.01.org
> Cc: Ruiyu Ni <ruiyu...@intel.com>
> Subject: [edk2] [patch 2/8] FatPkg\EnhancedFatDxe: Initialize variable after
> declaration
>
> Cc: Ruiyu Ni <ruiyu...@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Dandan Bi <dandan...@intel.com>
> ---
> FatPkg/EnhancedFatDxe/Misc.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/FatPkg/EnhancedFatDxe/Misc.c b/FatPkg/EnhancedFatDxe/Misc.c
> index f91759c..6ad688c 100644
> --- a/FatPkg/EnhancedFatDxe/Misc.c
> +++ b/FatPkg/EnhancedFatDxe/Misc.c
> @@ -696,15 +696,27 @@ Returns:
> TRUE - The time is valid.
> FALSE - The time is not valid.
>
> --*/
> {
> - static UINT8 MonthDays[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30,
> 31 };
> + STATIC UINT8 MonthDays[12];
> UINTN Day;
> BOOLEAN ValidTime;
>
> ValidTime = TRUE;
> + MonthDays[0] = 31;
> + MonthDays[1] = 28;
> + MonthDays[2] = 31;
> + MonthDays[3] = 30;
> + MonthDays[4] = 31;
> + MonthDays[5] = 30;
> + MonthDays[6] = 31;
> + MonthDays[7] = 31;
> + MonthDays[8] = 30;
> + MonthDays[9] = 31;
> + MonthDays[10] = 30;
> + MonthDays[11] = 31;
>
> //
> // Check the fields for range problems
> // Fat can only support from 1980
> //
> --
> 1.9.5.msysgit.1
>
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