llvm dev - Nov 2010 - [LLVMdev] LLVM BUG for x86 code generation ?

HI All,

when I compiled attached .ll file with llc 2.8 as follows:

llc -O0 -march=x86 llvmfails.ll -o llvmfails.s
gcc -m32 llvmfails.s -o llvmfails
./llvmfails

the executable exits with the expected message: "SUCCESS", whereas if
I use -O1 instead of -O0 for LLC, it prints out FAILS.

llc -O0 -march=x86 llvmfails.ll -o llvmfails.s
gcc -m32 llvmfails.s -o llvmfails
./llvmfails

As far as I can tell code generation for select instruction is not correct, It
seems that sign-extension propagation convert a sign-extension into a
zero-extend.
Routine to look at is:

@result = internal global i32 0
define void @test() {
L.entry:
        %__.I0000610 = alloca i32
        call void  @init()
        %0 = load i32* @t
        %1 = icmp eq i32 %0, 0
        %2 = zext i1 %1 to i32
        %3 = trunc i32 %2 to i1
        %4 = load i8* @uc
        %5 = zext i8 %4 to i32
        %6 = load i8* @sc
        %7 = sext i8 %6 to i32
        %8 = select  i1 %3, i32 %5, i32 %7
        store i32 %8, i32* %__.I0000610
        %9 = load i32* %__.I0000610
        call void  @seti(i32* @result, i32 %9)
        ret void
}


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HI All,

when I compiled attached .ll file with llc 2.8 as follows:

llc -O0 -march=x86 llvmfails.ll -o llvmfails.s
gcc -m32 llvmfails.s -o llvmfails
./llvmfails

the executable exits with the expected message: "SUCCESS", whereas if
I use -O1 instead of -O0 for LLC, it prints out FAILS.

llc -O0 -march=x86 llvmfails.ll -o llvmfails.s
gcc -m32 llvmfails.s -o llvmfails
./llvmfails

As far as I can tell code generation for select instruction is not correct, It
seems that sign-extension propagation convert a sign-extension into a
zero-extend.
Routine to look at is:

@result = internal global i32 0
define void @test() {
L.entry:
        %__.I0000610 = alloca i32
        call void  @init()
        %0 = load i32* @t
        %1 = icmp eq i32 %0, 0
        %2 = zext i1 %1 to i32
        %3 = trunc i32 %2 to i1
        %4 = load i8* @uc
        %5 = zext i8 %4 to i32
        %6 = load i8* @sc
        %7 = sext i8 %6 to i32
        %8 = select  i1 %3, i32 %5, i32 %7
        store i32 %8, i32* %__.I0000610
        %9 = load i32* %__.I0000610
        call void  @seti(i32* @result, i32 %9)
        ret void
}

Can you confirm that ?
Best Regards
Seb


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Hi Sebastian,
> when I compiled attached .ll file with llc 2.8 as follows:
>
> llc -O0 -march=x86 llvmfails.ll -o llvmfails.s
> gcc -m32 llvmfails.s -o llvmfails
> ./llvmfails
>
> the executable exits with the expected message: "SUCCESS",
whereas if I use -O1 instead of -O0 for LLC, it prints out FAILS.
>
> llc -O0 -march=x86 llvmfails.ll -o llvmfails.s
> gcc -m32 llvmfails.s -o llvmfails
> ./llvmfails
does the attached patch fix your problems?

Ciao,

Duncan.

PS: In the future please open a bug report when reporting a bug.
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Hi Duncan,

I've patched LLVM 2.8 source tree, and it doesn't fix the problem on my
side.
Did you checked that your patch fixes the problem ?

Best Regards
Seb

-----Original Message-----
From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
Behalf Of Duncan Sands
Sent: Thursday, November 18, 2010 12:48 PM
To: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] LLVM BUG for x86 code generation ?

Hi Sebastian,
> when I compiled attached .ll file with llc 2.8 as follows:
>
> llc -O0 -march=x86 llvmfails.ll -o llvmfails.s gcc -m32 llvmfails.s -o 
> llvmfails ./llvmfails
>
> the executable exits with the expected message: "SUCCESS",
whereas if I use -O1 instead of -O0 for LLC, it prints out FAILS.
>
> llc -O0 -march=x86 llvmfails.ll -o llvmfails.s gcc -m32 llvmfails.s -o 
> llvmfails ./llvmfails
does the attached patch fix your problems?

Ciao,

Duncan.

PS: In the future please open a bug report when reporting a bug.