[LLVMdev] CFG modifcations and code gen

Villmow, Micah Micah.Villmow at amd.com
Tue Oct 14 09:16:00 PDT 2008

But, the branch folding pass, or whatever passes are supposed to reorder
the blocks based on the CFG, are not doing so in this case. Otherwise
there is no way that blocks 2 and 4 should be printing out before blocks
3 & 5. Renumber blocks just seems to reorder the values based on their
pre-set block number, but when the CFG is modified these number should
modified also to follow the new ordering, which is not occurring. 



From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
On Behalf Of Dale Johannesen
Sent: Monday, October 13, 2008 5:28 PM
To: LLVM Developers Mailing List
Subject: Re: [LLVMdev] CFG modifcations and code gen



On Oct 13, 2008, at 5:14 PMPDT, Villmow, Micah wrote:

As stated in an earlier email, I am working on getting break/continue to
work correctly for my backend, but I ran into another issue with codegen
and the CFG. It seems that code gen is not done based on the CFG, but
rather on the block numbers, and the function call
MachineFunction::RenumberBlocks doesn't renumber the blocks based on the
CFG. So how can I modify the CFG so that when codegen occurs, it follows
the graph and not just does a linear scan over the MachineBasicBlock


It's not intended to work that way.  The BranchFolding pass, which runs
later, is responsible for rearranging things into a more reasonable



	In the attached dot file, block 2 gets printed before block 3
and 5 and block 4 gets printed between blocks 3 and 5. This obviously is
not what the CFG is saying it should be done. The code I'm using to do
this transformation, which takes 2 & 4 and places them after block 5 is:

	    MachineBasicBlock* newExitPath = findLowestNumSuccBB(root);



NULL, false);

pHigh->CorrectExtraCFGEdges(*pHigh->succ_begin(), newExitPath, false);




	So what am I doing wrong?





	Micah Villmow

	Systems Engineer

	Advanced Technology & Performance

	Advanced Micro Devices Inc.

	4555 Great America Pkwy,

	Santa Clara, CA. 95054

	P: 408-572-6219

	F: 408-572-6596


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