[fpc-devel] Finally fixed that MOVZX/SX optimisation!

[Florian Klämpfl]

Am 20.02.20 um 21:50 schrieb J. Gareth Moreton:
> Oh, sorry, I made a slight error.  The sequences only appear if you 
> specify -Oonoconstprop (and -a).  So that sequence is produced with 
> "\pp\bin\x86_64-win64\ppcx64 -O4 -Oonoconstprop -a test\cg\tcnvint3b.pp"

Then this is a non-issue.

> 
> There are still some inefficient combinations though in the assembly - 
> for example:
> 
>      movl    $61441,%eax
>      movw    $61441,%ax

This is with full -O3? Did you try to add -Oodeadstore?

> 
> Gareth aka. Kit
> 
> On 20/02/2020 20:45, J. Gareth Moreton wrote:
>> On 20/02/2020 20:34, Florian Klämpfl wrote:
>>> Am 20.02.20 um 21:25 schrieb J. Gareth Moreton:
>>>> but if you run all of the "test/cg/tcnvint3" tests with the "-a" 
>>>> option, you will notice such sequences in some of the ".s" file.
>>>
>>> With full -O3?
>>
>> Indeed so, with full -O4 even.  When compiling "/test/cg/tcnvint3.pp" 
>> (a test that already exists) with -O4, we get things like this in the 
>> assembler dump - command line = "\pp\bin\x86_64-win64\ppcx64 -O4 
>> test\cg\tcnvint3b.pp":
>>
>> # Peephole Optimization: movq $16711680,%rax -> movl $16711680,%eax 
>> (immediate can be represented with just 32 bits)
>>     movl    $16711680,%eax
>>     cmpl    $16711680,%eax
>>     je    .Lj29
>>     call    P$TCNVINT3_$$_FAIL
>>     jmp    .Lj30
>>     .p2align 4,,10
>>     .p2align 3
>> .Lj29:
>>
>> In this case, unless there's a freak CPU error, everything between "je 
>> .Lj29" and its destination label will never execute (if "je .Lj29" is 
>> changed to "jmp .Lj29", everything between them will be stripped by 
>> pass 1 of the peephole optimiser).
>>
>> Gareth aka. Kit
>>
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