Sanjiv.Gupta at microchip.com
2008-Oct-22 18:09 UTC
[LLVMdev] clobbering other physical registers in storeRegtoStackSlot.
In our case, storeRegToStackSlot, loadRegFromStackSlot clobbers some other physical register which may be holding a live value used somewhere else. How do I make regalloc aware so that it saves the value before storeRegToStackSlot and make it available again at the point of earlier use? TIA, Sanjiv -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20081022/c6d37ae4/attachment.html>
Evan Cheng
2008-Oct-23 18:17 UTC
[LLVMdev] clobbering other physical registers in storeRegtoStackSlot.
On Oct 22, 2008, at 11:09 AM, Sanjiv.Gupta at microchip.com wrote:> In our case, storeRegToStackSlot, loadRegFromStackSlot clobbers some > other physical register which may be holding a live value used > somewhere else. How do I make regalloc aware so that it saves the > value before storeRegToStackSlot and make it available again at the > point of earlier use? >Typical solution is to either reserve a register for these purposes so the backend does not have to worry about its value being clobbered. A better solution would be to teach these routines to make use of the register scavenger (or rather the callers should use the scavenger and pass the handle to these routines) to find a scratch register. It will require some changes to the target independent portion of codegen though. Evan> > > TIA, > Sanjiv > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20081023/213b11f9/attachment.html>
sanjiv gupta
2008-Oct-28 10:57 UTC
[LLVMdev] clobbering other physical registers in storeRegtoStackSlot.
On Thu, 2008-10-23 at 11:17 -0700, Evan Cheng wrote:> > On Oct 22, 2008, at 11:09 AM, Sanjiv.Gupta at microchip.com wrote: > > > In our case, storeRegToStackSlot, loadRegFromStackSlot clobbers some > > other physical register which may be holding a live value used > > somewhere else. How do I make regalloc aware so that it saves the > > value before storeRegToStackSlot and make it available again at the > > point of earlier use? > > > > > > > Typical solution is to either reserve a register for these purposes so > the backend does not have to worry about its value being clobbered.We have only one register (BSR) which we need to set correctly before every load/store. Setting up this register is done via an operation called 'banksel'. The problem is that spill/reload gets in between a banksel and load/store operation; and these spill/reload also modify BSR. Regalloc fails to recognize this and does not ReMat 'banksel' again before the load/store.> A better solution would be to teach these routines to make use of the > register scavenger (or rather the callers should use the scavenger and > pass the handle to these routines) to find a scratch register. It will > require some changes to the target independent portion of codegen > though. > > > Evan > > > > > > TIA, > > Sanjiv > > > > > > > > _______________________________________________ > > LLVM Developers mailing list > > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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