Yes, I know this works peachy keen for char arrays. I'm looking at (which
is
hard to express in C) something like
void foo () {
int bar[20] = { 42, 42, ..., 42 };
}
I don't want to do a memcopy of the 20 element constant array, and memset
doesn't work here. I want an intrinsic that copys the scalar int constant
42
to each element of the int array.
bagel
On 11/10/2016 03:30 PM, Mehdi Amini wrote:> Hi,
>
> An alternative is to perform what is done for the equivalent C construct:
>
> void foo() {
> char bar[20] = “hello”;
> }
>
> ->
>
> @foo.bar = private unnamed_addr constant [20 x i8]
c"hello\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00", align 16
> define void @foo() #0 {
> %1 = alloca [20 x i8], align 16
> %2 = bitcast [20 x i8]* %1 to i8*
> call void @llvm.memcpy.p0i8.p0i8.i64(i8* %2, i8* getelementptr inbounds
([20 x i8], [20 x i8]* @foo.bar, i32 0, i32 0), i64 20, i32 16, i1 false)
> ret void
> }
>
>
> —
> Mehdi
Like a list initializer, but will do partials/slices? Are you just looking to create an intrinsic that will generate a jump to a lib routine? On Thu, Nov 10, 2016 at 5:02 PM, Bagel via llvm-dev <llvm-dev at lists.llvm.org> wrote:> Yes, I know this works peachy keen for char arrays. I'm looking at (which > is > hard to express in C) something like > > void foo () { > int bar[20] = { 42, 42, ..., 42 }; > } > > I don't want to do a memcopy of the 20 element constant array, and memset > doesn't work here. I want an intrinsic that copys the scalar int constant > 42 > to each element of the int array. > > bagel > > > On 11/10/2016 03:30 PM, Mehdi Amini wrote: > > Hi, > > > > An alternative is to perform what is done for the equivalent C construct: > > > > void foo() { > > char bar[20] = “hello”; > > } > > > > -> > > > > @foo.bar = private unnamed_addr constant [20 x i8] > c"hello\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00", align 16 > > define void @foo() #0 { > > %1 = alloca [20 x i8], align 16 > > %2 = bitcast [20 x i8]* %1 to i8* > > call void @llvm.memcpy.p0i8.p0i8.i64(i8* %2, i8* getelementptr > inbounds ([20 x i8], [20 x i8]* @foo.bar, i32 0, i32 0), i64 20, i32 16, i1 > false) > > ret void > > } > > > > > > — > > Mehdi > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161110/c9aa075d/attachment.html>
Back in the day, we called this a BLT (block transfer, pronouced 'blit')
for the PDP-10 instruction of that name.
You can do this by assigning the first value, then do an overlapping memcpy to
fill in the rest.
There's probably something clever you can do with vector instructions too,
in many cases.
--paulr
From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Ryan
Taylor via llvm-dev
Sent: Thursday, November 10, 2016 2:08 PM
To: Bagel; llvm-dev
Subject: Re: [llvm-dev] array fill idioms
Like a list initializer, but will do partials/slices?
Are you just looking to create an intrinsic that will generate a jump to a lib
routine?
On Thu, Nov 10, 2016 at 5:02 PM, Bagel via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Yes, I know this works peachy keen for char arrays. I'm looking at (which
is
hard to express in C) something like
void foo () {
int bar[20] = { 42, 42, ..., 42 };
}
I don't want to do a memcopy of the 20 element constant array, and memset
doesn't work here. I want an intrinsic that copys the scalar int constant
42
to each element of the int array.
bagel
On 11/10/2016 03:30 PM, Mehdi Amini wrote:> Hi,
>
> An alternative is to perform what is done for the equivalent C construct:
>
> void foo() {
> char bar[20] = “hello”;
> }
>
> ->
>
> @foo.bar = private unnamed_addr constant [20 x i8]
c"hello\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00", align 16
> define void @foo() #0 {
> %1 = alloca [20 x i8], align 16
> %2 = bitcast [20 x i8]* %1 to i8*
> call void @llvm.memcpy.p0i8.p0i8.i64(i8* %2, i8* getelementptr inbounds
([20 x i8], [20 x i8]* @foo.bar, i32 0, i32 0), i64 20, i32 16, i1 false)
> ret void
> }
>
>
> —
> Mehdi
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On 11/10/2016 04:07 PM, Ryan Taylor wrote:> Like a list initializer, but will do partials/slices? >More than just an initializer, and yes it must do partials/slices. More like std:fill in C++;> Are you just looking to create an intrinsic that will generate a jump to a lib > routine? >If all else fails, then call a library routine. But if the number of elements is "small" and suitably aligned, them perhaps several elements can be filled by a simple load a constant and store.> On Thu, Nov 10, 2016 at 5:02 PM, Bagel via llvm-dev <llvm-dev at lists.llvm.org > <mailto:llvm-dev at lists.llvm.org>> wrote: > > Yes, I know this works peachy keen for char arrays. I'm looking at (which is > hard to express in C) something like > > void foo () { > int bar[20] = { 42, 42, ..., 42 }; > } > > I don't want to do a memcopy of the 20 element constant array, and memset > doesn't work here. I want an intrinsic that copys the scalar int constant 42 > to each element of the int array. > > bagel