[regalloc] How to access the Virtual Registers Map?

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1

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

2

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