[llvm-dev] [regalloc] How to access the Virtual Registers Map?

[Quentin Colombet via llvm-dev]

Hi Dominique,

If you want to access this map, you need to add your pass after
register allocation but before the VirtRegRewriter pass.
You have a target hook for that: addPreRewrite.

Cheers,
-Quentin

2018-06-05 2:37 GMT-07:00 Dominique Torette via llvm-dev
<llvm-dev at lists.llvm.org>:
> Hi,
>
> After Virtual Registers allocation, I would like to access and process the Registers Map assosiated to a function.
> I'm interested to retreive the number of different physical registers required to map all the virtual registers.
> (In the example here below, only two physical registers are required to map the 13 remaining virtual registers).
>
> With "regalloc" debug option enabled, the following dump is produced by VirtRegRewriter::runOnMachineFunction()
>
>  ********** REWRITE VIRTUAL REGISTERS **********
> ********** Function: _start
> ********** REGISTER MAP **********
> [%vreg2 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg3 -> %FA_ROFF2] FPUaOffsetClass
> [%vreg4 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg5 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg6 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg7 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg8 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg9 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg10 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg11 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg12 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg13 -> %FA_ROFF1] FPUaOffsetClass
> [%vreg14 -> %FA_ROFF2] FPUaOffsetClass
>
> To produce this dump, this function first call:
>   VRM = &getAnalysis<VirtRegMap>();
>
> But at the end of the same function, virtual registers allocation seems to be cleared:
>   VRM->clearAllVirt();
>   MRI->clearVirtRegs();
>
> Is there any simple hook around the VirtRegRewriter to retreive and process this Register Map.
> Any suggestions are welcome...
>
> Regards, Dominique T.
>
> Dominique Torette
> System Architect
> Rue des Chasseurs Ardennais - Liège Science Park - B-4031 Angleur
> Tel: +32 (0) 4 361 81 11 - Fax: +32 (0) 4 361 81 20
> www.spacebel.be
>
>
>
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