liuyu11@ict.ac.cn via llvm-dev
2016-Dec-28 07:09 UTC
[llvm-dev] why clang compile local to global
Hello,everyone:
I want to known how to let clang compile my local array to local variables:
I have the code :
int main()
{
int a[3]={1,2,3};
int b=7;
int c=8;
int d=9;
int e=10;
int f=11;
test(b,c,d,e,f,a);
return 0;
}
I use clang command:clang --target=mipsel -emit-llvm -S a.c -o a.ll
The a.ll is:
@main.a = private unnamed_addr constant [3 x i32] [i32 1, i32 2, i32 3], align 4
define i32 @main() #0 {
entry:
%retval = alloca i32, align 4
%a = alloca [3 x i32], align 4
%b = alloca i32, align 4
%c = alloca i32, align 4
%d = alloca i32, align 4
%e = alloca i32, align 4
%f = alloca i32, align 4
store i32 0, i32* %retval
%0 = bitcast [3 x i32]* %a to i8*
call void @llvm.memcpy.p0i8.p0i8.i32(i8* %0, i8* bitcast ([3 x i32]* @main.a
to i8*), i32 12, i32 4, i1 false)
store i32 7, i32* %b, align 4
store i32 8, i32* %c, align 4
store i32 9, i32* %d, align 4
store i32 10, i32* %e, align 4
store i32 11, i32* %f, align 4
%1 = load i32, i32* %b, align 4
%2 = load i32, i32* %c, align 4
%3 = load i32, i32* %d, align 4
%4 = load i32, i32* %e, align 4
%5 = load i32, i32* %f, align 4
%arraydecay = getelementptr inbounds [3 x i32], [3 x i32]* %a, i32 0, i32 0
call void @test(i32 signext %1, i32 signext %2, i32 signext %3, i32 signext
%4, i32 signext %5, i32* %arraydecay)
ret i32 0;}
I want to known how to compile local array a to a local variable
Thank you
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Mehdi Amini via llvm-dev
2016-Dec-28 07:17 UTC
[llvm-dev] why clang compile local to global
> On Dec 27, 2016, at 11:09 PM, liuyu11 at ict.ac.cn via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Hello,everyone: > I want to known how to let clang compile my local array to local variables: > I have the code : > int main() > { > int a[3]={1,2,3}; > > int b=7; > int c=8; > int d=9; > int e=10; > int f=11; > test(b,c,d,e,f,a); > return 0; > } > I use clang command:clang --target=mipsel -emit-llvm -S a.c -o a.ll > The a.ll is: > @main.a = private unnamed_addr constant [3 x i32] [i32 1, i32 2, i32 3], align 4 > define i32 @main() #0 { > entry: > %retval = alloca i32, align 4 > %a = alloca [3 x i32], align 4 > %b = alloca i32, align 4 > %c = alloca i32, align 4 > %d = alloca i32, align 4 > %e = alloca i32, align 4 > %f = alloca i32, align 4 > store i32 0, i32* %retval > %0 = bitcast [3 x i32]* %a to i8* > call void @llvm.memcpy.p0i8.p0i8.i32(i8* %0, i8* bitcast ([3 x i32]* @main.a to i8*), i32 12, i32 4, i1 false) > store i32 7, i32* %b, align 4 > store i32 8, i32* %c, align 4 > store i32 9, i32* %d, align 4 > store i32 10, i32* %e, align 4 > store i32 11, i32* %f, align 4 > %1 = load i32, i32* %b, align 4 > %2 = load i32, i32* %c, align 4 > %3 = load i32, i32* %d, align 4 > %4 = load i32, i32* %e, align 4 > %5 = load i32, i32* %f, align 4 > %arraydecay = getelementptr inbounds [3 x i32], [3 x i32]* %a, i32 0, i32 0 > call void @test(i32 signext %1, i32 signext %2, i32 signext %3, i32 signext %4, i32 signext %5, i32* %arraydecay) > ret i32 0;} > I want to known how to compile local array a to a local variableYour question is not totally clear: a *is* a “local variable” on the stack, this is the line:> %a = alloca [3 x i32], align 4It is initialized here:> call void @llvm.memcpy.p0i8.p0i8.i32(i8* %0, i8* bitcast ([3 x i32]* @main.a to i8*), i32 12, i32 4, i1 false)using the constant data that is stored in a global:> @main.a = private unnamed_addr constant [3 x i32] [i32 1, i32 2, i32 3], align 4What would you like the code to look like? — Mehdi
liuyu11@ict.ac.cn via llvm-dev
2016-Dec-28 09:42 UTC
[llvm-dev] why clang compile local to global
Hello，Mehdi
Thanks for your answer，I am writing a llvm backend for my team DSP.
The code is a testcase , but when I compile the code and running it ，I can
not get the correct result.
In the generating machine code, it loads the array value from a
"strange " address not in the stack , but I can not get where the
address value comes from , so I look up the .ll file.
With your help, I know variable "a" is really in the stack, the
"main.a" variable is constant global, and llvm.memcpy initialize the
"a" array , I have misunderstood the .ll file.
Then I see the assemble file , I find
.type $main.a, at object # @main.a
.section .rodata,"a", at progbits
.align 2
$main.a:
.4byte 1 # 0x1
.4byte 2 # 0x2
.4byte 3 # 0x3
.size $main.a, 12
the "main.a" is in the rotata section
Then I look up my ld script , I do not put the rodata section in the data
section ,so the value from the "strange" address is wrong . I finally
know why it get the array from the "strange " address.
Now it works perfect.
Thank you for your patient and help ,my English is not very good,Thank you .
刘钰
From: Mehdi Amini
Date: 2016-12-28 15:17
To: liuyu11 at ict.ac.cn
CC: llvm-dev; llvm-dev-request
Subject: Re: [llvm-dev] why clang compile local to global
> On Dec 27, 2016, at 11:09 PM, liuyu11 at ict.ac.cn via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> Hello,everyone:
> I want to known how to let clang compile my local array to local
variables:
> I have the code :
> int main()
> {
> int a[3]={1,2,3};
>
> int b=7;
> int c=8;
> int d=9;
> int e=10;
> int f=11;
> test(b,c,d,e,f,a);
> return 0;
> }
> I use clang command:clang --target=mipsel -emit-llvm -S a.c -o a.ll
> The a.ll is:
> @main.a = private unnamed_addr constant [3 x i32] [i32 1, i32 2, i32 3],
align 4
> define i32 @main() #0 {
> entry:
> %retval = alloca i32, align 4
> %a = alloca [3 x i32], align 4
> %b = alloca i32, align 4
> %c = alloca i32, align 4
> %d = alloca i32, align 4
> %e = alloca i32, align 4
> %f = alloca i32, align 4
> store i32 0, i32* %retval
> %0 = bitcast [3 x i32]* %a to i8*
> call void @llvm.memcpy.p0i8.p0i8.i32(i8* %0, i8* bitcast ([3 x i32]*
@main.a to i8*), i32 12, i32 4, i1 false)
> store i32 7, i32* %b, align 4
> store i32 8, i32* %c, align 4
> store i32 9, i32* %d, align 4
> store i32 10, i32* %e, align 4
> store i32 11, i32* %f, align 4
> %1 = load i32, i32* %b, align 4
> %2 = load i32, i32* %c, align 4
> %3 = load i32, i32* %d, align 4
> %4 = load i32, i32* %e, align 4
> %5 = load i32, i32* %f, align 4
> %arraydecay = getelementptr inbounds [3 x i32], [3 x i32]* %a, i32 0, i32
0
> call void @test(i32 signext %1, i32 signext %2, i32 signext %3, i32
signext %4, i32 signext %5, i32* %arraydecay)
> ret i32 0;}
> I want to known how to compile local array a to a local variable
Your question is not totally clear: a *is* a “local variable” on the stack, this
is the line:> %a = alloca [3 x i32], align 4
It is initialized here:
> call void @llvm.memcpy.p0i8.p0i8.i32(i8* %0, i8* bitcast ([3 x i32]*
@main.a to i8*), i32 12, i32 4, i1 false)
using the constant data that is stored in a global:
> @main.a = private unnamed_addr constant [3 x i32] [i32 1, i32 2, i32 3],
align 4
What would you like the code to look like?
—
Mehdi
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liuyu11@ict.ac.cn via llvm-dev
2016-Dec-28 09:59 UTC
[llvm-dev] why clang compile local to global
Hi Mehdi
I want to know how to generate the IR ,that do not use the “main.a” global
constant variable, and llvm.memcpy intrinsic , instead of liking other local
variable initialization :
store i32 7, i32* %b, align 4
For example :
%element0 = getelementptr inbounds [3 x i32]* %a, i32 0, i32 0
store i32 1, i32* %element0, align 4
%element1 = getelementptr inbounds [3 x i32]* %a, i32 0, i32 1
store i32 2, i32* %element1, align 4
Thank you
> On Dec 27, 2016, at 11:09 PM, liuyu11 at ict.ac.cn via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> Hello,everyone:
> I want to known how to let clang compile my local array to local
variables:
> I have the code :
> int main()
> {
> int a[3]={1,2,3};
>
> int b=7;
> int c=8;
> int d=9;
> int e=10;
> int f=11;
> test(b,c,d,e,f,a);
> return 0;
> }
> I use clang command:clang --target=mipsel -emit-llvm -S a.c -o a.ll
> The a.ll is:
> @main.a = private unnamed_addr constant [3 x i32] [i32 1, i32 2, i32 3],
align 4
> define i32 @main() #0 {
> entry:
> %retval = alloca i32, align 4
> %a = alloca [3 x i32], align 4
> %b = alloca i32, align 4
> %c = alloca i32, align 4
> %d = alloca i32, align 4
> %e = alloca i32, align 4
> %f = alloca i32, align 4
> store i32 0, i32* %retval
> %0 = bitcast [3 x i32]* %a to i8*
> call void @llvm.memcpy.p0i8.p0i8.i32(i8* %0, i8* bitcast ([3 x i32]*
@main.a to i8*), i32 12, i32 4, i1 false)
> store i32 7, i32* %b, align 4
> store i32 8, i32* %c, align 4
> store i32 9, i32* %d, align 4
> store i32 10, i32* %e, align 4
> store i32 11, i32* %f, align 4
> %1 = load i32, i32* %b, align 4
> %2 = load i32, i32* %c, align 4
> %3 = load i32, i32* %d, align 4
> %4 = load i32, i32* %e, align 4
> %5 = load i32, i32* %f, align 4
> %arraydecay = getelementptr inbounds [3 x i32], [3 x i32]* %a, i32 0, i32
0
> call void @test(i32 signext %1, i32 signext %2, i32 signext %3, i32
signext %4, i32 signext %5, i32* %arraydecay)
> ret i32 0;}
> I want to known how to compile local array a to a local variable
Your question is not totally clear: a *is* a “local variable” on the stack, this
is the line:> %a = alloca [3 x i32], align 4
It is initialized here:
> call void @llvm.memcpy.p0i8.p0i8.i32(i8* %0, i8* bitcast ([3 x i32]*
@main.a to i8*), i32 12, i32 4, i1 false)
using the constant data that is stored in a global:
> @main.a = private unnamed_addr constant [3 x i32] [i32 1, i32 2, i32 3],
align 4
What would you like the code to look like?
―
Mehdi
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