[compiler-rt] r215295 - builtins: correct __umodsi3, __udivsi3 on ARM

[Bill Wendling]

Jim & Owen

What do you think?

-bw

On Aug 10, 2014, at 1:06 PM, Saleem Abdulrasool <compnerd at compnerd.org> wrote:

> Hi Bill,
> 
> I realize that we are somewhat late in the cycle, but I think that this should be merged into the 3.5 branch.  Currently, an invocation of __umodsi3 in a compiler-rt built with clang 3.5 for an ARM chip with idiv may fault (if you are lucky) or plain corrupt memory.
> 
> The change is limited to ARMv7 with idiv and ARMv8 chips.
> 
> On Sat, Aug 9, 2014 at 1:17 PM, Saleem Abdulrasool <compnerd at compnerd.org> wrote:
> Author: compnerd
> Date: Sat Aug  9 15:17:37 2014
> New Revision: 215295
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=215295&view=rev
> Log:
> builtins: correct __umodsi3, __udivsi3 on ARM
> 
> When building the builtins for a modern CPU (idiv support), __umodsi3 was
> completely incorrect as it would behave as __udivmosi3, which takes a tertiary
> parameter which is a pointer.
> 
> __udivsi3 was also incorrect, returning the remainder in r1.  Although this
> would not result in any crash or invalid behaviour as r1 is a caller saved
> register in AAPCS, this is unnecessary.  Simply perform the division ignoring
> 
> Modified:
>     compiler-rt/trunk/lib/builtins/arm/udivsi3.S
>     compiler-rt/trunk/lib/builtins/arm/umodsi3.S
> 
> Modified: compiler-rt/trunk/lib/builtins/arm/udivsi3.S
> URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/builtins/arm/udivsi3.S?rev=215295&r1=215294&r2=215295&view=diff
> ==============================================================================
> --- compiler-rt/trunk/lib/builtins/arm/udivsi3.S (original)
> +++ compiler-rt/trunk/lib/builtins/arm/udivsi3.S Sat Aug  9 15:17:37 2014
> @@ -27,9 +27,7 @@ DEFINE_COMPILERRT_FUNCTION(__udivsi3)
>  #if __ARM_ARCH_EXT_IDIV__
>         tst     r1, r1
>         beq     LOCAL_LABEL(divby0)
> -       mov     r3, r0
> -       udiv    r0, r3, r1
> -       mls     r1, r0, r1, r3
> +       udiv    r0, r0, r1
>         bx      lr
>  #else
>         cmp     r1, #1
> 
> Modified: compiler-rt/trunk/lib/builtins/arm/umodsi3.S
> URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/builtins/arm/umodsi3.S?rev=215295&r1=215294&r2=215295&view=diff
> ==============================================================================
> --- compiler-rt/trunk/lib/builtins/arm/umodsi3.S (original)
> +++ compiler-rt/trunk/lib/builtins/arm/umodsi3.S Sat Aug  9 15:17:37 2014
> @@ -25,10 +25,8 @@ DEFINE_COMPILERRT_FUNCTION(__umodsi3)
>  #if __ARM_ARCH_EXT_IDIV__
>         tst     r1, r1
>         beq     LOCAL_LABEL(divby0)
> -       mov     r3, r0
> -       udiv    r0, r3, r1
> -       mls     r1, r0, r1, r3
> -       str     r1, [r2]
> +       udiv    r2, r0, r1
> +       mls     r0, r2, r1, r0
>         bx      lr
>  #else
>         cmp     r1, #1
> 
> 
> _______________________________________________
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> 
> 
> 
> -- 
> Saleem Abdulrasool
> compnerd (at) compnerd (dot) org

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