On Thursday, 24 October 2019 at 21:02:03 UTC, Per Nordlöw wrote:
> On Thursday, 24 October 2019 at 18:37:05 UTC, welkam wrote:
>> I remember in some video Chandler Carruth said that value range propagation across function boundary was implemented in llvm but later removed because it produced no performance improvement for C and C++ code. I wonder how it fare when used on D code.
>
> Interesting. What uses of VRP do you see in D?

Now that you asked I realized that it wont be that much useful because in D all arrays go together with their size so cross function VRP would do little.

On 10/25/2019 05:37 AM, Stefan Koch wrote:

> just replace x = a[i] with x = a.ptr[i];

That's a neat trick!

Ali

On Friday, 25 October 2019 at 15:22:12 UTC, Ali Çehreli wrote:
> On 10/25/2019 05:37 AM, Stefan Koch wrote:
>
>> just replace x = a[i] with x = a.ptr[i];
>
> That's a neat trick!
>
> Ali

But it requires the function to be qualified as @trusted which might hide a @system == operator. How common is it for a == operator to be unsafe?

On Wednesday, 23 October 2019 at 11:20:59 UTC, Per Nordlöw wrote:
> Does DMD/LDC avoid range-checking in slice-expressions such as the one in my array-overload of `startsWith` defined as
>
> bool startsWith(T)(scope const(T)[] haystack,
>                    scope const(T)[] needle)
> {
>     if (haystack.length >= needle.length)
>     {
>         return haystack[0 .. needle.length] == needle; // is slice range checking avoid here?
>     }
>     return false;
> }

LDC is good at optimizing simple patterns, the only pitfall I know is https://forum.dlang.org/post/eoftnwkannqmubhjotat@forum.dlang.org

On Wednesday, 23 October 2019 at 13:51:19 UTC, kinke wrote:
> You call this messy?!
>
> cmpq	%rdi, %rdx
> 	jae	.LBB0_2
> 	xorl	%eax, %eax
> 	retq
> .LBB0_2:
> 	movq	%rdi, %rax
> 	testq	%rdi, %rdi
> 	je	.LBB0_3
> 	pushq	%rax
> 	.cfi_def_cfa_offset 16
> 	movq	%rcx, %rdi
> 	movq	%rax, %rdx
> 	callq	memcmp@PLT
> 	testl	%eax, %eax
> 	sete	%al
> 	addq	$8, %rsp
> 	.cfi_def_cfa_offset 8
> 	retq
> .LBB0_3:
> 	movb	$1, %al
> 	retq

No, this is fine. Thanks.

On Friday, 25 October 2019 at 21:33:26 UTC, Per Nordlöw wrote:
> But it requires the function to be qualified as @trusted which might hide a @system == operator. How common is it for a == operator to be unsafe?

Ping.

On Wednesday, 23 October 2019 at 11:20:59 UTC, Per Nordlöw wrote:
> Does DMD/LDC avoid range-checking in slice-expressions such as the one in my array-overload of `startsWith` defined as
>
> bool startsWith(T)(scope const(T)[] haystack,
>                    scope const(T)[] needle)
> {
>     if (haystack.length >= needle.length)
>     {
>         return haystack[0 .. needle.length] == needle; // is slice range checking avoid here?
>     }
>     return false;
> }

LDC is good at optimizing simple patterns, the only pitfall I know is https://forum.dlang.org/post/eoftnwkannqmubhjotat@forum.dlang.org