[llvm-commits] [patch] - Bugfix for TargetLowering::SimplifySetCC

[Evan Cheng]

Thanks Eli.

Evan
On Jul 29, 2010, at 11:50 PM, Eli Friedman wrote:

> Not actually my code (I only reindented it); in any case, fixed in r109854.
> 
> -Eli
> 
> On Thu, Jul 29, 2010 at 10:52 PM, Evan Cheng <evan.cheng at apple.com> wrote:
>> Sorry I completely missed this patch. I agree there is a bug here but I don't know this code well enough to determine if this is the right fix. Eli, you wrote the optimization. Do you mind take a look at this?
>> 
>> Evan
>> 
>> On May 20, 2010, at 6:17 AM, Evzen Muller wrote:
>> 
>>> Hi all,
>>> 
>>> When I compile this code (clang generates something similar for bitfield
>>> access):
>>> 
>>> target datalayout = "e-p:32:32-f64:32:32-i64:32:32-n32"
>>> target triple = "arm-none-eabi"
>>> 
>>> define i32 @extend2bit_v2(i32 %val) {
>>> entry:
>>>  %0 = trunc i32 %val to i2                       ; <i2> [#uses=1]
>>>  %1 = sext i2 %0 to i32                          ; <i32> [#uses=1]
>>>  %2 = icmp eq i32 %1, 3                          ; <i1> [#uses=1]
>>>  %3 = zext i1 %2 to i32                          ; <i32> [#uses=1]
>>>  ret i32 %3
>>> }
>>> 
>>> ARM codegen produces:
>>> @ BB#0:                                 @ %entry
>>>        and     r1, r0, #3
>>>        mov     r0, #0
>>>        cmp     r1, #3
>>>        moveq   r0, #1
>>>        bx      lr
>>> 
>>> This is not correct, because when %val == 3 this will return 1, but expected
>>> result is 0 because i2 constant (3) should be sign-extended before icmp.
>>> 
>>> There is an optimization in TargetLowering::SimplifySetCC (around line 1790)
>>> which works fine if C1 has more or less active bits than ExtSrcTyBits, but I
>>> think that if C1.getActiveBits() == ExtSrcTyBits we should do normal
>>> truncate/sign-extend.
>>> 
>>> Attached patch should fix this problem.
>>> 
>>> Thanks
>>> Evzen
>>> 
>>> <simplify_setcc_bugfix.patch>_______________________________________________
>>> llvm-commits mailing list
>>> llvm-commits at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>> 
>>