vivek pandya via llvm-dev
2016-Jun-26 16:35 UTC
[llvm-dev] Tail call optimization is getting affected due to local function related optimization with IPRA
According to this http://llvm.org/docs/CodeGenerator.html#tail-call-section, it seems that adding a new CC for the purpose of local function optimization seems a good idea because tail call optimization only takes place when both caller and callee have fastcc or GHC or HiPE calling convention. -Vivek On Sun, Jun 26, 2016 at 1:26 AM, vivek pandya <vivekvpandya at gmail.com> wrote:> > > On Sat, Jun 25, 2016 at 11:03 PM, vivek pandya <vivekvpandya at gmail.com> > wrote: > >> Hello LLVM Community, >> >> To improve Interprocedural Register Allocation (IPRA) we are trying to >> force caller >> saved registers for local functions (which has likage type local). To >> achive it >> I have modified TargetFrameLowering::determineCalleeSaves() to return >> early for >> function which satisfies if (F->hasLocalLinkage() && >> !F->hasAddressTaken()) and >> also reflecting the fact that for local function there are no caller >> saved registers >> I am also changing RegUsageInfoCollector.cpp to not to mark regiseters as >> callee >> saved in RegMask due to CC with follwoing change in code: >> >> if (!F->hasLocalLinkage() || F->hasAddressTaken()) { >> const uint32_t *CallPreservedMask >> TRI->getCallPreservedMask(MF, MF.getFunction()->getCallingConv()); >> // Set callee saved register as preserved. >> for (unsigned i = 0; i < RegMaskSize; ++i) >> RegMask[i] = RegMask[i] | CallPreservedMask[i]; >> } >> >> For more details please follow following link. >> https://groups.google.com/d/msg/llvm-dev/XRzGhJ9wtZg/bYFMzppXEwAJ >> >> Now consider following bug due to forcing caller saved registers for >> local function >> when IPRA enable: >> >> void makewt(int nw, int *ip, double *w) { >> ... >> bitrv2(nw, ip, w); >> } >> >> here bitrv2 is local fuction and for that when IPRA enable callee saved >> registers >> are set to none. So for that function following is set of collbered >> register as >> per regmaks collected by RegUsageInfoCollector pass. >> >> Function Name : bitrv2 >> Clobbered Registers: >> AH AL AX BH BL BP BPL BX CH CL CX DI DIL EAX EBP EBX ECX EDI EFLAGS ESI >> ESP RAX >> RBP RBX RCX RDI RSI RSP SI SIL SP SPL R8 R9 R10 R11 R12 R13 R14 R15 R8B >> R9B R10B >> R11B R12B R13B R14B R15B R8D R9D R10D R11D R12D R13D R14D R15D R8W R9W >> R10W R11W >> R12W R13W R14W R15W >> >> How ever caller of bitrv2, makewt has callee saved registers as per CC, >> but this >> code results in segmentation fault when compliled with O1 because makewt >> has value >> of *ip in R14 register and that is stored and restore by makewt at >> begining of call >> but due to tail call optimization following code is generated and here >> bitrv2 does >> not preserve R14 so whwn execution returns to main (which is caller of >> makewt) >> value of *ip is gone from R14 (which sould not) and when main calls >> makewt again >> then value of *ip (R14) is wrong and result into segmentation fault. >> >> Assembly code of makewt: >> _makewt: >> ... >> popq %rbx >> popq %r12 >> popq %r13 >> popq %r14 >> popq %r15 >> popq %rbp >> jmp _bitrv2 ## TAILCALL >> > > A very naive solution to this problem come to me is to convert above code > to following: > > _makewt: > ... > jmp _bitrv2 ## TAILCALL > popq %rbx > popq %r12 > popq %r13 > popq %r14 > popq %r15 > popq %rbp > > So that when _bitrv2 returns caller will over write callee saved register > ( as per CC of that function ) to correct values. > I wanted to try it out but I am not able to find correct code where I can > do that. > -Vivek > >> >> There is one more case of faluire due to local function related >> optimization. >> I am analysing that (sorry for taking more time but I am not much good at >> assembly). >> >> I need some hints for how to solve this. If you feel some problem with my >> analyses >> please let me know if you want me to send generated .s file and source .c >> file. >> >> Sincerely, >> Vivek >> > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160626/7e2c5d16/attachment.html>
vivek pandya via llvm-dev
2016-Jun-27 16:25 UTC
[llvm-dev] Tail call optimization is getting affected due to local function related optimization with IPRA
Hello , To solve this bug locally I have given preference to tail call optimization over local function related optimization in IPRA. I have added following method to achieve this: bool isEligibleForTailCallOptimization(Function *F) { CallingConv::ID CC = F->getCallingConv(); if (CC == CallingConv::Fast || CC == CallingConv::GHC || CC =CallingConv::HiPE) return true; return false; } Any other suggestions are always welcomed. and I am checking this condition along with hasLocalLinkage() and hasAddressTaken(). Due to this test-suite now has only 2 runtime failure where as before this there were around 43 due to local function related optimization. But of course by giving preference to tail call many opportunities to optimize IPRA is missed. The 2 existing failure are interesting and hard to debug, namely they are MultiSource/Applications/SPASS/SPASS and MultiSource/Applications/sqlite3/sqlite3 However for test-suite sqlite3 is only complied as CLI program and thus it only contains 2 (big) source files. In sqlite3 source code there are few static methods with variable number of arguments and due to that these static function should not get tail call optimized and thus IPRA optimization can be done but I am digging more into this to know reason of failures. Sincerely, Vivek On Sun, Jun 26, 2016 at 10:05 PM, vivek pandya <vivekvpandya at gmail.com> wrote:> According to this > http://llvm.org/docs/CodeGenerator.html#tail-call-section, it seems that > adding a new CC for the purpose of local function optimization seems a good > idea because tail call optimization only takes place when both caller and > callee have fastcc or GHC or HiPE calling convention. > > -Vivek > > > On Sun, Jun 26, 2016 at 1:26 AM, vivek pandya <vivekvpandya at gmail.com> > wrote: > >> >> >> On Sat, Jun 25, 2016 at 11:03 PM, vivek pandya <vivekvpandya at gmail.com> >> wrote: >> >>> Hello LLVM Community, >>> >>> To improve Interprocedural Register Allocation (IPRA) we are trying to >>> force caller >>> saved registers for local functions (which has likage type local). To >>> achive it >>> I have modified TargetFrameLowering::determineCalleeSaves() to return >>> early for >>> function which satisfies if (F->hasLocalLinkage() && >>> !F->hasAddressTaken()) and >>> also reflecting the fact that for local function there are no caller >>> saved registers >>> I am also changing RegUsageInfoCollector.cpp to not to mark regiseters >>> as callee >>> saved in RegMask due to CC with follwoing change in code: >>> >>> if (!F->hasLocalLinkage() || F->hasAddressTaken()) { >>> const uint32_t *CallPreservedMask >>> TRI->getCallPreservedMask(MF, >>> MF.getFunction()->getCallingConv()); >>> // Set callee saved register as preserved. >>> for (unsigned i = 0; i < RegMaskSize; ++i) >>> RegMask[i] = RegMask[i] | CallPreservedMask[i]; >>> } >>> >>> For more details please follow following link. >>> https://groups.google.com/d/msg/llvm-dev/XRzGhJ9wtZg/bYFMzppXEwAJ >>> >>> Now consider following bug due to forcing caller saved registers for >>> local function >>> when IPRA enable: >>> >>> void makewt(int nw, int *ip, double *w) { >>> ... >>> bitrv2(nw, ip, w); >>> } >>> >>> here bitrv2 is local fuction and for that when IPRA enable callee saved >>> registers >>> are set to none. So for that function following is set of collbered >>> register as >>> per regmaks collected by RegUsageInfoCollector pass. >>> >>> Function Name : bitrv2 >>> Clobbered Registers: >>> AH AL AX BH BL BP BPL BX CH CL CX DI DIL EAX EBP EBX ECX EDI EFLAGS ESI >>> ESP RAX >>> RBP RBX RCX RDI RSI RSP SI SIL SP SPL R8 R9 R10 R11 R12 R13 R14 R15 R8B >>> R9B R10B >>> R11B R12B R13B R14B R15B R8D R9D R10D R11D R12D R13D R14D R15D R8W R9W >>> R10W R11W >>> R12W R13W R14W R15W >>> >>> How ever caller of bitrv2, makewt has callee saved registers as per CC, >>> but this >>> code results in segmentation fault when compliled with O1 because makewt >>> has value >>> of *ip in R14 register and that is stored and restore by makewt at >>> begining of call >>> but due to tail call optimization following code is generated and here >>> bitrv2 does >>> not preserve R14 so whwn execution returns to main (which is caller of >>> makewt) >>> value of *ip is gone from R14 (which sould not) and when main calls >>> makewt again >>> then value of *ip (R14) is wrong and result into segmentation fault. >>> >>> Assembly code of makewt: >>> _makewt: >>> ... >>> popq %rbx >>> popq %r12 >>> popq %r13 >>> popq %r14 >>> popq %r15 >>> popq %rbp >>> jmp _bitrv2 ## TAILCALL >>> >> >> A very naive solution to this problem come to me is to convert above code >> to following: >> >> _makewt: >> ... >> jmp _bitrv2 ## TAILCALL >> popq %rbx >> popq %r12 >> popq %r13 >> popq %r14 >> popq %r15 >> popq %rbp >> >> So that when _bitrv2 returns caller will over write callee saved register >> ( as per CC of that function ) to correct values. >> I wanted to try it out but I am not able to find correct code where I can >> do that. >> -Vivek >> >>> >>> There is one more case of faluire due to local function related >>> optimization. >>> I am analysing that (sorry for taking more time but I am not much good >>> at assembly). >>> >>> I need some hints for how to solve this. If you feel some problem with >>> my analyses >>> please let me know if you want me to send generated .s file and source >>> .c file. >>> >>> Sincerely, >>> Vivek >>> >> >> >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160627/e4f5865f/attachment.html>
vivek pandya via llvm-dev
2016-Jun-28 05:51 UTC
[llvm-dev] Tail call optimization is getting affected due to local function related optimization with IPRA
On Mon, Jun 27, 2016 at 9:55 PM, vivek pandya <vivekvpandya at gmail.com> wrote:> Hello , > > To solve this bug locally I have given preference to tail call > optimization over local function related optimization in IPRA. I have added > following method to achieve this: > > bool isEligibleForTailCallOptimization(Function *F) { > CallingConv::ID CC = F->getCallingConv(); > if (CC == CallingConv::Fast || CC == CallingConv::GHC || CC => CallingConv::HiPE) > return true; > return false; >I have changed above code to : auto Attr = F->getFnAttribute("disable-tail-calls"); if (Attr.getValueAsString() == "true") return false; return true; this disables local function related optimization for functions which may get tail call. but with any of above code most of the opportunities are missed for example sqlite3's module sqlite3 has more than 500 static function but none of them getting optimized for local function. Also according to this http://llvm.org/docs/CodeGenerator.html#tail-call-section , on x86 and power pc while generating PIC function with local linkage are considered for tail call optimization. But this may not be the case on other architecture. After adding above check I have noticed some improvements in test-suite ( no failures ) but this needs to be benchmark again ( specially with 43 failure which were reported before, because those test-cases are having some local function for sure and need to check if any of them is getting optimized. Other wise tail call and local function related optimization can not be together. So just optimizing functions with local linkage is not a good idea instead it should be based on some call frequency analysis and in such case if required we can suppress tail call elimination to give preference to spill code movement. I am looking into " Register Allocation Across Procedure and Module Boundaries" http://dl.acm.org/citation.cfm?id=93551. This paper basically extends very similar idea of propagating register usage information in call graph as functions are compiled in bottom up order. I am trying to find some way so that we can push spill code out of frequently called procedures so that we can improve runtime. Sincerely, Vivek }> > Any other suggestions are always welcomed. > > and I am checking this condition along with hasLocalLinkage() and > hasAddressTaken(). > > Due to this test-suite now has only 2 runtime failure where as before this > there were around 43 due to local function related optimization. But of > course by giving preference to tail call many opportunities to optimize > IPRA is missed. > > The 2 existing failure are interesting and hard to debug, namely they are > MultiSource/Applications/SPASS/SPASS and > MultiSource/Applications/sqlite3/sqlite3 > > However for test-suite sqlite3 is only complied as CLI program and thus it > only contains 2 (big) source files. In sqlite3 source code there are few > static methods with variable number of arguments and due to that these > static function should not get tail call optimized and thus IPRA > optimization can be done but I am digging more into this to know reason of > failures. > > Sincerely, > Vivek > > > On Sun, Jun 26, 2016 at 10:05 PM, vivek pandya <vivekvpandya at gmail.com> > wrote: > >> According to this >> http://llvm.org/docs/CodeGenerator.html#tail-call-section, it seems that >> adding a new CC for the purpose of local function optimization seems a good >> idea because tail call optimization only takes place when both caller and >> callee have fastcc or GHC or HiPE calling convention. >> >> -Vivek >> >> >> On Sun, Jun 26, 2016 at 1:26 AM, vivek pandya <vivekvpandya at gmail.com> >> wrote: >> >>> >>> >>> On Sat, Jun 25, 2016 at 11:03 PM, vivek pandya <vivekvpandya at gmail.com> >>> wrote: >>> >>>> Hello LLVM Community, >>>> >>>> To improve Interprocedural Register Allocation (IPRA) we are trying to >>>> force caller >>>> saved registers for local functions (which has likage type local). To >>>> achive it >>>> I have modified TargetFrameLowering::determineCalleeSaves() to return >>>> early for >>>> function which satisfies if (F->hasLocalLinkage() && >>>> !F->hasAddressTaken()) and >>>> also reflecting the fact that for local function there are no caller >>>> saved registers >>>> I am also changing RegUsageInfoCollector.cpp to not to mark regiseters >>>> as callee >>>> saved in RegMask due to CC with follwoing change in code: >>>> >>>> if (!F->hasLocalLinkage() || F->hasAddressTaken()) { >>>> const uint32_t *CallPreservedMask >>>> TRI->getCallPreservedMask(MF, >>>> MF.getFunction()->getCallingConv()); >>>> // Set callee saved register as preserved. >>>> for (unsigned i = 0; i < RegMaskSize; ++i) >>>> RegMask[i] = RegMask[i] | CallPreservedMask[i]; >>>> } >>>> >>>> For more details please follow following link. >>>> https://groups.google.com/d/msg/llvm-dev/XRzGhJ9wtZg/bYFMzppXEwAJ >>>> >>>> Now consider following bug due to forcing caller saved registers for >>>> local function >>>> when IPRA enable: >>>> >>>> void makewt(int nw, int *ip, double *w) { >>>> ... >>>> bitrv2(nw, ip, w); >>>> } >>>> >>>> here bitrv2 is local fuction and for that when IPRA enable callee saved >>>> registers >>>> are set to none. So for that function following is set of collbered >>>> register as >>>> per regmaks collected by RegUsageInfoCollector pass. >>>> >>>> Function Name : bitrv2 >>>> Clobbered Registers: >>>> AH AL AX BH BL BP BPL BX CH CL CX DI DIL EAX EBP EBX ECX EDI EFLAGS ESI >>>> ESP RAX >>>> RBP RBX RCX RDI RSI RSP SI SIL SP SPL R8 R9 R10 R11 R12 R13 R14 R15 R8B >>>> R9B R10B >>>> R11B R12B R13B R14B R15B R8D R9D R10D R11D R12D R13D R14D R15D R8W R9W >>>> R10W R11W >>>> R12W R13W R14W R15W >>>> >>>> How ever caller of bitrv2, makewt has callee saved registers as per CC, >>>> but this >>>> code results in segmentation fault when compliled with O1 because >>>> makewt has value >>>> of *ip in R14 register and that is stored and restore by makewt at >>>> begining of call >>>> but due to tail call optimization following code is generated and here >>>> bitrv2 does >>>> not preserve R14 so whwn execution returns to main (which is caller of >>>> makewt) >>>> value of *ip is gone from R14 (which sould not) and when main calls >>>> makewt again >>>> then value of *ip (R14) is wrong and result into segmentation fault. >>>> >>>> Assembly code of makewt: >>>> _makewt: >>>> ... >>>> popq %rbx >>>> popq %r12 >>>> popq %r13 >>>> popq %r14 >>>> popq %r15 >>>> popq %rbp >>>> jmp _bitrv2 ## TAILCALL >>>> >>> >>> A very naive solution to this problem come to me is to convert above >>> code to following: >>> >>> _makewt: >>> ... >>> jmp _bitrv2 ## TAILCALL >>> popq %rbx >>> popq %r12 >>> popq %r13 >>> popq %r14 >>> popq %r15 >>> popq %rbp >>> >>> So that when _bitrv2 returns caller will over write callee saved >>> register ( as per CC of that function ) to correct values. >>> I wanted to try it out but I am not able to find correct code where I >>> can do that. >>> -Vivek >>> >>>> >>>> There is one more case of faluire due to local function related >>>> optimization. >>>> I am analysing that (sorry for taking more time but I am not much good >>>> at assembly). >>>> >>>> I need some hints for how to solve this. If you feel some problem with >>>> my analyses >>>> please let me know if you want me to send generated .s file and source >>>> .c file. >>>> >>>> Sincerely, >>>> Vivek >>>> >>> >>> >> >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160628/4e1b71a7/attachment.html>
Mehdi Amini via llvm-dev
2016-Jun-28 14:41 UTC
[llvm-dev] Tail call optimization is getting affected due to local function related optimization with IPRA
> On Jun 27, 2016, at 12:25 PM, vivek pandya <vivekvpandya at gmail.com> wrote: > > Hello , > > To solve this bug locally I have given preference to tail call optimization over local function related optimization in IPRA. I have added following method to achieve this: > > bool isEligibleForTailCallOptimization(Function *F) { > CallingConv::ID CC = F->getCallingConv(); > if (CC == CallingConv::Fast || CC == CallingConv::GHC || CC == CallingConv::HiPE) > return true; > return false; > } > > Any other suggestions are always welcomed.Why aren’t checking for the presence of a tail call? — Mehdi> > and I am checking this condition along with hasLocalLinkage() and hasAddressTaken(). > > Due to this test-suite now has only 2 runtime failure where as before this there were around 43 due to local function related optimization. But of course by giving preference to tail call many opportunities to optimize IPRA is missed. > > The 2 existing failure are interesting and hard to debug, namely they are MultiSource/Applications/SPASS/SPASS and MultiSource/Applications/sqlite3/sqlite3 > > However for test-suite sqlite3 is only complied as CLI program and thus it only contains 2 (big) source files. In sqlite3 source code there are few static methods with variable number of arguments and due to that these static function should not get tail call optimized and thus IPRA optimization can be done but I am digging more into this to know reason of failures. > > Sincerely, > Vivek > > > On Sun, Jun 26, 2016 at 10:05 PM, vivek pandya <vivekvpandya at gmail.com <mailto:vivekvpandya at gmail.com>> wrote: > According to this http://llvm.org/docs/CodeGenerator.html#tail-call-section <http://llvm.org/docs/CodeGenerator.html#tail-call-section>, it seems that adding a new CC for the purpose of local function optimization seems a good idea because tail call optimization only takes place when both caller and callee have fastcc or GHC or HiPE calling convention. > > -Vivek > > > On Sun, Jun 26, 2016 at 1:26 AM, vivek pandya <vivekvpandya at gmail.com <mailto:vivekvpandya at gmail.com>> wrote: > > > On Sat, Jun 25, 2016 at 11:03 PM, vivek pandya <vivekvpandya at gmail.com <mailto:vivekvpandya at gmail.com>> wrote: > Hello LLVM Community, > > To improve Interprocedural Register Allocation (IPRA) we are trying to force caller > saved registers for local functions (which has likage type local). To achive it > I have modified TargetFrameLowering::determineCalleeSaves() to return early for > function which satisfies if (F->hasLocalLinkage() && !F->hasAddressTaken()) and > also reflecting the fact that for local function there are no caller saved registers > I am also changing RegUsageInfoCollector.cpp to not to mark regiseters as callee > saved in RegMask due to CC with follwoing change in code: > > if (!F->hasLocalLinkage() || F->hasAddressTaken()) { > const uint32_t *CallPreservedMask > TRI->getCallPreservedMask(MF, MF.getFunction()->getCallingConv()); > // Set callee saved register as preserved. > for (unsigned i = 0; i < RegMaskSize; ++i) > RegMask[i] = RegMask[i] | CallPreservedMask[i]; > } > > For more details please follow following link. > https://groups.google.com/d/msg/llvm-dev/XRzGhJ9wtZg/bYFMzppXEwAJ <https://groups.google.com/d/msg/llvm-dev/XRzGhJ9wtZg/bYFMzppXEwAJ> > > Now consider following bug due to forcing caller saved registers for local function > when IPRA enable: > > void makewt(int nw, int *ip, double *w) { > ... > bitrv2(nw, ip, w); > } > > here bitrv2 is local fuction and for that when IPRA enable callee saved registers > are set to none. So for that function following is set of collbered register as > per regmaks collected by RegUsageInfoCollector pass. > > Function Name : bitrv2 > Clobbered Registers: > AH AL AX BH BL BP BPL BX CH CL CX DI DIL EAX EBP EBX ECX EDI EFLAGS ESI ESP RAX > RBP RBX RCX RDI RSI RSP SI SIL SP SPL R8 R9 R10 R11 R12 R13 R14 R15 R8B R9B R10B > R11B R12B R13B R14B R15B R8D R9D R10D R11D R12D R13D R14D R15D R8W R9W R10W R11W > R12W R13W R14W R15W > > How ever caller of bitrv2, makewt has callee saved registers as per CC, but this > code results in segmentation fault when compliled with O1 because makewt has value > of *ip in R14 register and that is stored and restore by makewt at begining of call > but due to tail call optimization following code is generated and here bitrv2 does > not preserve R14 so whwn execution returns to main (which is caller of makewt) > value of *ip is gone from R14 (which sould not) and when main calls makewt again > then value of *ip (R14) is wrong and result into segmentation fault. > > Assembly code of makewt: > _makewt: > ... > popq %rbx > popq %r12 > popq %r13 > popq %r14 > popq %r15 > popq %rbp > jmp _bitrv2 ## TAILCALL > > A very naive solution to this problem come to me is to convert above code to following: > > _makewt: > ... > jmp _bitrv2 ## TAILCALL > popq %rbx > popq %r12 > popq %r13 > popq %r14 > popq %r15 > popq %rbp > > So that when _bitrv2 returns caller will over write callee saved register ( as per CC of that function ) to correct values. > I wanted to try it out but I am not able to find correct code where I can do that. > -Vivek > > There is one more case of faluire due to local function related optimization. > I am analysing that (sorry for taking more time but I am not much good at assembly). > > I need some hints for how to solve this. If you feel some problem with my analyses > please let me know if you want me to send generated .s file and source .c file. > > Sincerely, > Vivek > > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160628/2362a26d/attachment-0001.html>
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