[cfe-dev] Testcase for LLVM PR9350

[Friedman, Eli via cfe-dev]

On 1/3/2017 2:28 PM, via cfe-dev wrote:
> Hi clang devs,
>
> I was looking at PR9350 and saw that Eli added a test to check LLVM 
> doesn't overflow on [signed] char increment:
>
> --- cfe/trunk/test/CodeGen/integer-overflow.c 2011/03/02 01:43:30 126815
> +++ cfe/trunk/test/CodeGen/integer-overflow.c 2011/03/02 01:49:12 126816
> @@ -50,11 +50,17 @@
>    // TRAPV_HANDLER: foo(
>    --a;
>
> -
>    // -fwrapv should turn off inbounds for GEP's, PR9256
>    extern int* P;
>    ++P;
>    // DEFAULT: getelementptr inbounds i32*
>    // WRAPV: getelementptr i32*
>    // TRAPV: getelementptr inbounds i32*
> +
> +  // PR9350: char increment never overflows.
> +  extern volatile signed char PR9350;
> +  // DEFAULT: add i8 {{.*}}, 1
> +  // WRAPV: add i8 {{.*}}, 1
> +  // TRAPV: add i8 {{.*}}, 1
> +  ++PR9350;
> }
>
> http://llvm.org/viewvc/llvm-project?view=revision&revision=126816
>
> Presumably the logic about promotion to int applies the same as in the 
> argument John gave in PR9350 since 6.5.3.1 §3 says "the prefix -- 
> operator is analogous to the prefix ++ operator, except that the value 
> of the operand is decremented".
>
> Would it therefore make sense to add the equivalent test to 
> integer-overflow.c that decrement of a [signed] char didn't ever cause 
> underflow:
>
>   // DEFAULT: sub i8 {{.*}}, 1
>   // WRAPV: sub i8 {{.*}}, 1
>   // TRAPV: sub i8 {{.*}}, 1
>   --PR9350;
>

Yes, it probably makes sense to add a testcase like that.  Patch welcome.

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

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