Hello,
I am new here. This is my first post.
I spent about three days on trying out LLVM by developing a front-end which
is able to generate LLVM IR for a subset of C language. I have not applied
any optimization pass yet. On linux, it can go all the way through with the
system native assemlber and linker to generate executables. And it runs. I
ran into problems on Windows since the generated assembly code is not able
to be assembled by NASM.
Here is an example C code:
int gv;
int foo(int p)
{
int lv;
gv = p;
if (p > 5) {
lv = 0;
while (gv>0) {
lv = lv + gv;
gv = gv - 1;
}
}
else {
lv = 1;
while (gv>0) {
lv = lv * gv;
gv = gv - 1;
}
}
return lv;
}
Here is the LLVM IR I generated:
; ModuleID = 'my cool jit'
@gv = weak global i32 0 ; <i32*> [#uses=9]
define i32 @foo(i32 %p) {
entry:
%lv = alloca i32 ; <i32*> [#uses=8]
%p1 = alloca i32 ; <i32*> [#uses=3]
store i32 %p, i32* %p1
store i32 0, i32* %lv
%p2 = load i32* %p1 ; <i32> [#uses=1]
store i32 %p2, i32* @gv
%p3 = load i32* %p1 ; <i32> [#uses=1]
%0 = icmp ugt i32 %p3, 5 ; <i1> [#uses=1]
%1 = zext i1 %0 to i32 ; <i32> [#uses=1]
%2 = icmp ne i32 %1, 0 ; <i1> [#uses=1]
br i1 %2, label %then, label %else
then: ; preds = %entry
store i32 0, i32* %lv
br label %while
while: ; preds = %whilebody,
%then
%gv = load i32* @gv ; <i32> [#uses=1]
%3 = icmp ugt i32 %gv, 0 ; <i1> [#uses=1]
%4 = zext i1 %3 to i32 ; <i32> [#uses=1]
%5 = icmp ne i32 %4, 0 ; <i1> [#uses=1]
br i1 %5, label %whilebody, label %whilecont
whilebody: ; preds = %while
%lv4 = load i32* %lv ; <i32> [#uses=1]
%gv5 = load i32* @gv ; <i32> [#uses=1]
%6 = add i32 %lv4, %gv5 ; <i32> [#uses=1]
store i32 %6, i32* %lv
%gv6 = load i32* @gv ; <i32> [#uses=1]
%7 = sub i32 %gv6, 1 ; <i32> [#uses=1]
store i32 %7, i32* @gv
br label %while
whilecont: ; preds = %while
br label %ifcont
else: ; preds = %entry
store i32 1, i32* %lv
br label %while7
while7: ; preds = %whilebody9,
%else
%gv8 = load i32* @gv ; <i32> [#uses=1]
%8 = icmp ugt i32 %gv8, 0 ; <i1> [#uses=1]
%9 = zext i1 %8 to i32 ; <i32> [#uses=1]
%10 = icmp ne i32 %9, 0 ; <i1> [#uses=1]
br i1 %10, label %whilebody9, label %whilecont13
whilebody9: ; preds = %while7
%lv10 = load i32* %lv ; <i32> [#uses=1]
%gv11 = load i32* @gv ; <i32> [#uses=1]
%11 = mul i32 %lv10, %gv11 ; <i32> [#uses=1]
store i32 %11, i32* %lv
%gv12 = load i32* @gv ; <i32> [#uses=1]
%12 = sub i32 %gv12, 1 ; <i32> [#uses=1]
store i32 %12, i32* @gv
br label %while7
whilecont13: ; preds = %while7
br label %ifcont
ifcont: ; preds = %whilecont13,
%whilecont
%lv14 = load i32* %lv ; <i32> [#uses=1]
ret i32 %lv14
}
And here is the assembly code I generated with "llc -march=x86
-x86-asm-sytax=intel filename".
.686
.MMX
.XMM
.model flat
EXTERN _abort:near
.text
public _foo
ALIGN 16
_foo proc near
sub ESP, 8
$label1:
mov EAX, DWORD PTR [ESP + 12]
mov DWORD PTR [ESP], EAX
mov DWORD PTR [ESP + 4], 0
mov EAX, DWORD PTR [ESP]
mov DWORD PTR [_gv], EAX
cmp DWORD PTR [ESP], 6
jb $BB1_4
$BB1_1: ; %then
mov DWORD PTR [ESP + 4], 0
ALIGN 16
$BB1_2: ; %while
; Loop Depth 1
; Loop Header
; Inner Loop
cmp DWORD PTR [_gv], 0
je $BB1_7
$BB1_3: ; %whilebody
; Loop Depth 1
; Loop Header is
BB1_2
; Inner Loop
mov EAX, DWORD PTR [_gv]
add DWORD PTR [ESP + 4], EAX
dec DWORD PTR [_gv]
jmp $BB1_2
$BB1_4: ; %else
mov DWORD PTR [ESP + 4], 1
jmp $BB1_6
ALIGN 16
$BB1_5: ; %whilebody9
; Loop Depth 1
; Loop Header is
BB1_6
; Inner Loop
mov EAX, DWORD PTR [_gv]
imul EAX, DWORD PTR [ESP + 4]
mov DWORD PTR [ESP + 4], EAX
dec DWORD PTR [_gv]
$BB1_6: ; %while7
; Loop Depth 1
; Loop Header
; Inner Loop
cmp DWORD PTR [_gv], 0
jne $BB1_5
$BB1_7: ; %ifcont
mov EAX, DWORD PTR [ESP + 4]
add ESP, 8
ret
_foo endp
_gv? SEGEMNT PARA common 'COMMON'
_gv: ; gv
db 4 dup(0)
_gv? ends
end
The above assembly code cannot be assembled by NASM. I got the following
error message:
cg1.s:1: error: attempt to define a local label before any non-local labels
cg1.s:2: error: attempt to define a local label before any non-local labels
cg1.s:3: error: attempt to define a local label before any non-local labels
cg1.s:4: error: attempt to define a local label before any non-local labels
cg1.s:4: error: parser: instruction expected
cg1.s:6: error: binary format does not support any special symbol types
cg1.s:9: error: attempt to define a local label before any non-local labels
cg1.s:10: error: parser: instruction expected
cg1.s:12: error: parser: instruction expected
cg1.s:15: error: comma, colon or end of line expected
cg1.s:16: error: comma, colon or end of line expected
cg1.s:17: error: comma, colon or end of line expected
cg1.s:18: error: comma, colon or end of line expected
cg1.s:19: error: comma, colon or end of line expected
cg1.s:20: error: comma, colon or end of line expected
cg1.s:23: error: comma, colon or end of line expected
cg1.s:29: error: comma, colon or end of line expected
cg1.s:35: error: comma, colon or end of line expected
cg1.s:36: error: comma, colon or end of line expected
cg1.s:37: error: comma, colon or end of line expected
cg1.s:40: error: comma, colon or end of line expected
cg1.s:47: error: comma, colon or end of line expected
cg1.s:48: error: comma, colon or end of line expected
cg1.s:49: error: comma, colon or end of line expected
cg1.s:50: error: comma, colon or end of line expected
cg1.s:55: error: comma, colon or end of line expected
cg1.s:58: error: comma, colon or end of line expected
cg1.s:61: error: symbol `_foo' redefined
cg1.s:61: error: parser: instruction expected
cg1.s:62: error: parser: instruction expected
cg1.s:64: error: comma expected after operand 1
cg1.s:65: error: symbol `_gv?' redefined
cg1.s:65: error: parser: instruction expected
I am not sure whether there is any command line option that is required for
generating NASM assembly code. Looked into the document and command line
help. But I cannot find anything that helps. I would appreciate it if anyone
could provide some hint.
BTW: The getting started document with Visual Studio looks very
out-of-dated.
Thanks,
Bengu
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Anton Korobeynikov
2010-Jan-28 08:18 UTC
[LLVMdev] llc generated machine assembly code for NASM
Hello> system native assemlber and linker to generate executables. And it runs. I > ran into problems on Windows since the generated assembly code is not able > to be assembled by NASM.That's correct. Use AT&T asm printer and GNU as everywhere. Everything else is too weak to be usable and thus one should consider intel asm printer to be of "listing quality". -- With best regards, Anton Korobeynikov Faculty of Mathematics and Mechanics, Saint Petersburg State University
Thanks for Anton's reply. Does anybody have an idea of roughly how much effort is required to make intel asm printer to be usable? If it is within weeks, probably I can give it a try. Thanks, Bengu On Thu, Jan 28, 2010 at 12:18 AM, Anton Korobeynikov < anton at korobeynikov.info> wrote:> Hello > > > system native assemlber and linker to generate executables. And it > runs. I > > ran into problems on Windows since the generated assembly code is not > able > > to be assembled by NASM. > That's correct. Use AT&T asm printer and GNU as everywhere. Everything > else is too weak to be usable and thus one should consider intel asm > printer to be of "listing quality". > > -- > With best regards, Anton Korobeynikov > Faculty of Mathematics and Mechanics, Saint Petersburg State University >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20100128/a6577006/attachment.html>
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