[llvm] r174336 - [Stack Alignment] emit warning instead of a hard error

[Eric Christopher]

Having been in this argument at least 2 times I'm curious what the logic is
and since most of the list doesn't have access to radar... what's the
reason? This seems like something that should probably be wider discussed.

-eric


On Mon, Feb 4, 2013 at 3:45 PM, Manman Ren <mren at apple.com> wrote:

> Author: mren
> Date: Mon Feb  4 17:45:08 2013
> New Revision: 174336
>
> URL: http://llvm.org/viewvc/llvm-project?rev=174336&view=rev
> Log:
> [Stack Alignment] emit warning instead of a hard error
>
> Per discussion in rdar://13127907, we should emit a hard error only if
> people write code where the requested alignment is larger than achievable
> and assumes the low bits are zeros. A warning should be good enough when
> we are not sure if the source code assumes the low bits are zeros.
>
> rdar://13127907
>
> Modified:
>     llvm/trunk/lib/CodeGen/MachineFunction.cpp
>     llvm/trunk/test/CodeGen/ARM/alloc-no-stack-realign-error.ll
>
> Modified: llvm/trunk/lib/CodeGen/MachineFunction.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineFunction.cpp?rev=174336&r1=174335&r2=174336&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/MachineFunction.cpp (original)
> +++ llvm/trunk/lib/CodeGen/MachineFunction.cpp Mon Feb  4 17:45:08 2013
> @@ -479,11 +479,11 @@ static inline unsigned clampStackAlignme
>    if (!ShouldClamp || PrefAlign <= StackAlign)
>      return PrefAlign;
>    if (Alloca && MinAlign > StackAlign)
> -    Alloca->getParent()->getContext().emitError(Alloca,
> -        "Requested Minimal Alignment exceeds the Stack Alignment!");
> +    Alloca->getParent()->getContext().emitWarning(Alloca,
> +        "Requested alignment exceeds the stack alignment!");
>    else
>      assert(MinAlign <= StackAlign &&
> -           "Requested Minimal Alignment exceeds the Stack Alignment!");
> +           "Requested alignment exceeds the stack alignment!");
>    return StackAlign;
>  }
>
>
> Modified: llvm/trunk/test/CodeGen/ARM/alloc-no-stack-realign-error.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/alloc-no-stack-realign-error.ll?rev=174336&r1=174335&r2=174336&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/CodeGen/ARM/alloc-no-stack-realign-error.ll (original)
> +++ llvm/trunk/test/CodeGen/ARM/alloc-no-stack-realign-error.ll Mon Feb  4
> 17:45:08 2013
> @@ -6,10 +6,10 @@
>  ; If alignment for alloc is smaller than or equal to stack alignment, but
> the
>  ; preferred type alignment is bigger, the alignment will be clamped.
>  ; If alignment for alloca is bigger than stack alignment, the compiler
> -; will emit an error.
> +; will emit a warning.
>  define void @test(<16 x float>* noalias sret %agg.result) nounwind ssp {
>  entry:
> -; CHECK: Requested Minimal Alignment exceeds the Stack Alignment!
> +; CHECK: warning: Requested alignment exceeds the stack alignment!
>   %retval = alloca <16 x float>, align 16
>   %0 = load <16 x float>* @T3_retval, align 16
>   store <16 x float> %0, <16 x float>* %retval
>
>
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