Johnson, Nicholas Paul via llvm-dev
2017-Apr-24 16:10 UTC
[llvm-dev] Debugging UNREACHABLE "Couldn't join subrange" in RegisterCoalescer (out-of-tree backend)
Hello,
I have a minimal testcase which crashes RegisterCoalescer in my out-of-tree
target. It only crashes in Debug builds of llc---not in Release builds. Also,
interesting to note that the x86 backend lowers this same testcase successfully.
I did a quick search of bugs.llvm.org and found no matches.
This implies that the problem is in my backend and/or how my backend interacts
with RegisterCoalescer. I'm not too familiar with RegisterCoalescer. Can
anyone give me a hint on where I should start looking for the problem in my
backend?
Thank you,
Nick Johnson
D. E. Shaw Research
Here's my minimal testcase:
$ llvm-dis -o - bugpoint.reduced.simplified.bc
; ModuleID = 'bugpoint.reduced.simplified.bc'
source_filename = "bugpoint-output-7eb0c3b.bc"
target datalayout =
"e-m:e-p:32:32-i8:8:32-i16:16:32-i32:32:32-i64:64:64-v64:64:64-v128:128:128-n32-S128"
target triple = "desgcv3-unknown-elf"
; Function Attrs: noreturn nounwind
define void @wobble() local_unnamed_addr #0 {
%1 = extractelement <4 x i32> <i32 0, i32 2, i32 3, i32 4>, i32
undef
%2 = sub nsw i32 0, %1
%3 = icmp sgt i32 %2, 0
br i1 %3, label %4, label %5
; <label>:4: ; preds = %5, %0
unreachable
; <label>:5: ; preds = %0
%6 = extractelement <4 x i32> <i32 0, i32 2, i32 3, i32 4>, i32
undef
%7 = sub nsw i32 0, %6
%8 = icmp sgt i32 %7, 0
br i1 %8, label %9, label %4
; <label>:9: ; preds = %5
unreachable
}
attributes #0 = { noreturn nounwind
"correctly-rounded-divide-sqrt-fp-math"="false"
"disable-tail-calls"="false"
"less-precise-fpmad"="false"
"no-frame-pointer-elim"="true"
"no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false"
"no-jump-tables"="false"
"no-nans-fp-math"="false"
"no-signed-zeros-fp-math"="false"
"no-trapping-math"="false"
"stack-protector-buffer-size"="8"
"target-cpu"="generic"
"unsafe-fp-math"="false"
"use-soft-float"="false" }
Here's the tail-end of the log, with debugging turned on:
$llc bugpoint.reduced.simplified.bc -debug
...
208B %vreg13:sub_64_1<def> = COPY %vreg34:sub_64_1;
VecRegs:%vreg13,%vreg34
Considering merging to VecRegs with %vreg34 in %vreg13
RHS = %vreg34
[160r,240r:0)[240r,384B:1)[400B,480r:1)[480r,496r:2)[496r,672r:3) 0 at 160r 1
at 240r 2 at 480r 3 at 496r L00000020 [240r,384B:1)[400B,672r:1) 0 at x 1 at
240r L00000010 [160r,384B:1)[400B,672r:1) 0 at x 1 at 160r L00000002
[480r,480d:1)[496r,672r:0) 0 at 496r 1 at 480r L00000001 [480r,672r:0) 0 at
480r
LHS = %vreg13 [96r,112r:0)[112r,208r:1)[208r,288r:2) 0 at 96r 1
at 112r 2 at 208r L00000002 [96r,96d:1)[112r,288r:0) 0 at 112r 1 at 96r
L00000030 [208r,288r:1) 0 at x 1 at 208r L00000001 [96r,288r:0) 0 at 96r
merge %vreg13:2 at 208r into %vreg34:0 at 160r --> @160r
LHST = %vreg13 %vreg13 [96r,112r:0)[112r,208r:1)[208r,288r:2) 0
at 96r 1 at 112r 2 at 208r L00000002 [96r,96d:1)[112r,288r:0) 0 at 112r 1 at
96r L00000030 [208r,288r:1) 0 at x 1 at 208r L00000001 [96r,288r:0) 0 at 96r
Copy+Merge 00000030 into 00000020
Reduce Lane to 00000010
conflict at %vreg34:1 at 240r
*** Couldn't join subrange!
UNREACHABLE executed at
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2693!
#0 0x00000000027395af llvm::sys::PrintStackTrace(llvm::raw_ostream&)
/d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:402:0
#1 0x0000000002739971 PrintStackTraceSignalHandler(void*)
/d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:466:0
#2 0x0000000002737bce llvm::sys::RunSignalHandlers()
/d/en/johnsoni-0/gctools/llvm/lib/Support/Signals.cpp:44:0
#3 0x0000000002738f41 SignalHandler(int)
/d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:256:0
#4 0x000000396140f7e0 __restore_rt (/lib64/libpthread.so.0+0x396140f7e0)
#5 0x0000003960c325e5 __GI_raise (/lib64/libc.so.6+0x3960c325e5)
#6 0x0000003960c33dc5 __GI_abort (/lib64/libc.so.6+0x3960c33dc5)
#7 0x00000000026d4c42 bindingsErrorHandler(void*, std::string const&, bool)
/d/en/johnsoni-0/gctools/llvm/lib/Support/ErrorHandling.cpp:127:0
#8 0x0000000001fdbc85 (anonymous
namespace)::RegisterCoalescer::joinSubRegRanges(llvm::LiveRange&,
llvm::LiveRange&, llvm::LaneBitmask, llvm::CoalescerPair const&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2695:0
#9 0x0000000001fdc3df (anonymous
namespace)::RegisterCoalescer::mergeSubRangeInto(llvm::LiveInterval&,
llvm::LiveRange const&, llvm::LaneBitmask, llvm::CoalescerPair&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2769:0
#10 0x0000000001fdcbd5 (anonymous
namespace)::RegisterCoalescer::joinVirtRegs(llvm::CoalescerPair&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2832:0
#11 0x0000000001fdd174 (anonymous
namespace)::RegisterCoalescer::joinIntervals(llvm::CoalescerPair&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2892:0
#12 0x0000000001fd5fc3 (anonymous
namespace)::RegisterCoalescer::joinCopy(llvm::MachineInstr*, bool&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:1468:0
#13 0x0000000001fdd4b6 (anonymous
namespace)::RegisterCoalescer::copyCoalesceWorkList(llvm::MutableArrayRef<llvm::MachineInstr*>)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2962:0
#14 0x0000000001fddf32 (anonymous
namespace)::RegisterCoalescer::coalesceLocals()
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3087:0
#15 0x0000000001fde3a1 (anonymous
namespace)::RegisterCoalescer::joinAllIntervals()
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3121:0
#16 0x0000000001fde6e2 (anonymous
namespace)::RegisterCoalescer::runOnMachineFunction(llvm::MachineFunction&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3167:0
#17 0x0000000001d28d87
llvm::MachineFunctionPass::runOnFunction(llvm::Function&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/MachineFunctionPass.cpp:62:0
...
Matthias Braun via llvm-dev
2017-Apr-24 16:58 UTC
[llvm-dev] Debugging UNREACHABLE "Couldn't join subrange" in RegisterCoalescer (out-of-tree backend)
This looks like a bug related to the subregister liveness updating in the RegisterCoalescer. As this is always hard to debug without having the actual target at hand: - Make sure the testcase (or rather all testcases) passes `llc -verify-machineinstrs` - It would be good to see the full `llc -debug-only=regalloc` dump (looking below I would at least see which slotindexes belong to which instructions). Best to file a PR with the information. - There is one open PR about coalescing subregister liveness right now: http://llvm.org/PR32688 <http://llvm.org/PR32688> (but it's hard to say without investigation whether it is the same). - Matthias> On Apr 24, 2017, at 9:10 AM, Johnson, Nicholas Paul via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Hello, > > I have a minimal testcase which crashes RegisterCoalescer in my out-of-tree target. It only crashes in Debug builds of llc---not in Release builds. Also, interesting to note that the x86 backend lowers this same testcase successfully. I did a quick search of bugs.llvm.org and found no matches. > > This implies that the problem is in my backend and/or how my backend interacts with RegisterCoalescer. I'm not too familiar with RegisterCoalescer. Can anyone give me a hint on where I should start looking for the problem in my backend? > > Thank you, > Nick Johnson > D. E. Shaw Research > > > Here's my minimal testcase: > > $ llvm-dis -o - bugpoint.reduced.simplified.bc > ; ModuleID = 'bugpoint.reduced.simplified.bc' > source_filename = "bugpoint-output-7eb0c3b.bc" > target datalayout = "e-m:e-p:32:32-i8:8:32-i16:16:32-i32:32:32-i64:64:64-v64:64:64-v128:128:128-n32-S128" > target triple = "desgcv3-unknown-elf" > > ; Function Attrs: noreturn nounwind > define void @wobble() local_unnamed_addr #0 { > %1 = extractelement <4 x i32> <i32 0, i32 2, i32 3, i32 4>, i32 undef > %2 = sub nsw i32 0, %1 > %3 = icmp sgt i32 %2, 0 > br i1 %3, label %4, label %5 > > ; <label>:4: ; preds = %5, %0 > unreachable > > ; <label>:5: ; preds = %0 > %6 = extractelement <4 x i32> <i32 0, i32 2, i32 3, i32 4>, i32 undef > %7 = sub nsw i32 0, %6 > %8 = icmp sgt i32 %7, 0 > br i1 %8, label %9, label %4 > > ; <label>:9: ; preds = %5 > unreachable > } > > attributes #0 = { noreturn nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" } > > > Here's the tail-end of the log, with debugging turned on: > > $llc bugpoint.reduced.simplified.bc -debug > ... > 208B %vreg13:sub_64_1<def> = COPY %vreg34:sub_64_1; VecRegs:%vreg13,%vreg34 > Considering merging to VecRegs with %vreg34 in %vreg13 > RHS = %vreg34 [160r,240r:0)[240r,384B:1)[400B,480r:1)[480r,496r:2)[496r,672r:3) 0 at 160r 1 at 240r 2 at 480r 3 at 496r L00000020 [240r,384B:1)[400B,672r:1) 0 at x 1 at 240r L00000010 [160r,384B:1)[400B,672r:1) 0 at x 1 at 160r L00000002 [480r,480d:1)[496r,672r:0) 0 at 496r 1 at 480r L00000001 [480r,672r:0) 0 at 480r > LHS = %vreg13 [96r,112r:0)[112r,208r:1)[208r,288r:2) 0 at 96r 1 at 112r 2 at 208r L00000002 [96r,96d:1)[112r,288r:0) 0 at 112r 1 at 96r L00000030 [208r,288r:1) 0 at x 1 at 208r L00000001 [96r,288r:0) 0 at 96r > merge %vreg13:2 at 208r into %vreg34:0 at 160r --> @160r > LHST = %vreg13 %vreg13 [96r,112r:0)[112r,208r:1)[208r,288r:2) 0 at 96r 1 at 112r 2 at 208r L00000002 [96r,96d:1)[112r,288r:0) 0 at 112r 1 at 96r L00000030 [208r,288r:1) 0 at x 1 at 208r L00000001 [96r,288r:0) 0 at 96r > Copy+Merge 00000030 into 00000020 > Reduce Lane to 00000010 > conflict at %vreg34:1 at 240r > *** Couldn't join subrange! > > UNREACHABLE executed at /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2693! > #0 0x00000000027395af llvm::sys::PrintStackTrace(llvm::raw_ostream&) /d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:402:0 > #1 0x0000000002739971 PrintStackTraceSignalHandler(void*) /d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:466:0 > #2 0x0000000002737bce llvm::sys::RunSignalHandlers() /d/en/johnsoni-0/gctools/llvm/lib/Support/Signals.cpp:44:0 > #3 0x0000000002738f41 SignalHandler(int) /d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:256:0 > #4 0x000000396140f7e0 __restore_rt (/lib64/libpthread.so.0+0x396140f7e0) > #5 0x0000003960c325e5 __GI_raise (/lib64/libc.so.6+0x3960c325e5) > #6 0x0000003960c33dc5 __GI_abort (/lib64/libc.so.6+0x3960c33dc5) > #7 0x00000000026d4c42 bindingsErrorHandler(void*, std::string const&, bool) /d/en/johnsoni-0/gctools/llvm/lib/Support/ErrorHandling.cpp:127:0 > #8 0x0000000001fdbc85 (anonymous namespace)::RegisterCoalescer::joinSubRegRanges(llvm::LiveRange&, llvm::LiveRange&, llvm::LaneBitmask, llvm::CoalescerPair const&) /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2695:0 > #9 0x0000000001fdc3df (anonymous namespace)::RegisterCoalescer::mergeSubRangeInto(llvm::LiveInterval&, llvm::LiveRange const&, llvm::LaneBitmask, llvm::CoalescerPair&) /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2769:0 > #10 0x0000000001fdcbd5 (anonymous namespace)::RegisterCoalescer::joinVirtRegs(llvm::CoalescerPair&) /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2832:0 > #11 0x0000000001fdd174 (anonymous namespace)::RegisterCoalescer::joinIntervals(llvm::CoalescerPair&) /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2892:0 > #12 0x0000000001fd5fc3 (anonymous namespace)::RegisterCoalescer::joinCopy(llvm::MachineInstr*, bool&) /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:1468:0 > #13 0x0000000001fdd4b6 (anonymous namespace)::RegisterCoalescer::copyCoalesceWorkList(llvm::MutableArrayRef<llvm::MachineInstr*>) /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2962:0 > #14 0x0000000001fddf32 (anonymous namespace)::RegisterCoalescer::coalesceLocals() /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3087:0 > #15 0x0000000001fde3a1 (anonymous namespace)::RegisterCoalescer::joinAllIntervals() /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3121:0 > #16 0x0000000001fde6e2 (anonymous namespace)::RegisterCoalescer::runOnMachineFunction(llvm::MachineFunction&) /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3167:0 > #17 0x0000000001d28d87 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) /d/en/johnsoni-0/gctools/llvm/lib/CodeGen/MachineFunctionPass.cpp:62:0 > ... > > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev-------------- next part -------------- An HTML attachment was scrubbed... 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Johnson, Nicholas Paul via llvm-dev
2017-Apr-24 17:14 UTC
[llvm-dev] Debugging UNREACHABLE "Couldn't join subrange" in RegisterCoalescer (out-of-tree backend)
Thank you Matthias,
$ llc bugpoint-reduced-simplified.bc -verify-machineinstrs -debug-only=regalloc
-print-before-all 2>log
Result file 'log' is attached. None of the target-specific instructions
(LI, VEXT, BLT, J) do anything weird with registers.
I saw PR32688, but it looks like a different assertion failing.
One thing that struck me as odd was that RegisterCoalescer::joinVirtRegs
features this guard that looks very similar to the failed condition
// Some conflicts can only be resolved after all values have been mapped.
if (!LHSVals.resolveConflicts(RHSVals) || !RHSVals.resolveConflicts(LHSVals))
return false;
Compare that to the failed condition in RegisterCoalescer::joinSubRegRanges,
which is structurally quite similar but operates on (I think) sub-ranges of
those intervals previously tested.
if (!LHSVals.resolveConflicts(RHSVals) ||
!RHSVals.resolveConflicts(LHSVals)) {
// We already determined that it is legal to merge the intervals, so this
// should never fail.
llvm_unreachable("*** Couldn't join subrange!\n");
}
Nick Johnson
D. E. Shaw Research
From: mbraun at apple.com [mailto:mbraun at apple.com]
Sent: Monday, April 24, 2017 12:58 PM
To: Johnson, Nicholas Paul
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] Debugging UNREACHABLE "Couldn't join
subrange" in RegisterCoalescer (out-of-tree backend)
This looks like a bug related to the subregister liveness updating in the
RegisterCoalescer.
As this is always hard to debug without having the actual target at hand:
- Make sure the testcase (or rather all testcases) passes `llc
-verify-machineinstrs`
- It would be good to see the full `llc -debug-only=regalloc` dump (looking
below I would at least see which slotindexes belong to which instructions). Best
to file a PR with the information.
- There is one open PR about coalescing subregister liveness right now:
http://llvm.org/PR32688 (but it's hard to say without investigation whether
it is the same).
- Matthias
On Apr 24, 2017, at 9:10 AM, Johnson, Nicholas Paul via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Hello,
I have a minimal testcase which crashes RegisterCoalescer in my out-of-tree
target. It only crashes in Debug builds of llc---not in Release builds. Also,
interesting to note that the x86 backend lowers this same testcase successfully.
I did a quick search of bugs.llvm.org<http://bugs.llvm.org> and found no
matches.
This implies that the problem is in my backend and/or how my backend interacts
with RegisterCoalescer. I'm not too familiar with RegisterCoalescer. Can
anyone give me a hint on where I should start looking for the problem in my
backend?
Thank you,
Nick Johnson
D. E. Shaw Research
Here's my minimal testcase:
$ llvm-dis -o - bugpoint.reduced.simplified.bc
; ModuleID = 'bugpoint.reduced.simplified.bc'
source_filename = "bugpoint-output-7eb0c3b.bc"
target datalayout =
"e-m:e-p:32:32-i8:8:32-i16:16:32-i32:32:32-i64:64:64-v64:64:64-v128:128:128-n32-S128"
target triple = "desgcv3-unknown-elf"
; Function Attrs: noreturn nounwind
define void @wobble() local_unnamed_addr #0 {
%1 = extractelement <4 x i32> <i32 0, i32 2, i32 3, i32 4>, i32
undef
%2 = sub nsw i32 0, %1
%3 = icmp sgt i32 %2, 0
br i1 %3, label %4, label %5
; <label>:4: ; preds = %5, %0
unreachable
; <label>:5: ; preds = %0
%6 = extractelement <4 x i32> <i32 0, i32 2, i32 3, i32 4>, i32
undef
%7 = sub nsw i32 0, %6
%8 = icmp sgt i32 %7, 0
br i1 %8, label %9, label %4
; <label>:9: ; preds = %5
unreachable
}
attributes #0 = { noreturn nounwind
"correctly-rounded-divide-sqrt-fp-math"="false"
"disable-tail-calls"="false"
"less-precise-fpmad"="false"
"no-frame-pointer-elim"="true"
"no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false"
"no-jump-tables"="false"
"no-nans-fp-math"="false"
"no-signed-zeros-fp-math"="false"
"no-trapping-math"="false"
"stack-protector-buffer-size"="8"
"target-cpu"="generic"
"unsafe-fp-math"="false"
"use-soft-float"="false" }
Here's the tail-end of the log, with debugging turned on:
$llc bugpoint.reduced.simplified.bc -debug
...
208B %vreg13:sub_64_1<def> = COPY %vreg34:sub_64_1;
VecRegs:%vreg13,%vreg34
Considering merging to VecRegs with %vreg34 in %vreg13
RHS = %vreg34
[160r,240r:0)[240r,384B:1)[400B,480r:1)[480r,496r:2)[496r,672r:3) 0 at 160r 1
at 240r 2 at 480r 3 at 496r L00000020 [240r,384B:1)[400B,672r:1) 0 at x 1 at
240r L00000010 [160r,384B:1)[400B,672r:1) 0 at x 1 at 160r L00000002
[480r,480d:1)[496r,672r:0) 0 at 496r 1 at 480r L00000001 [480r,672r:0) 0 at
480r
LHS = %vreg13 [96r,112r:0)[112r,208r:1)[208r,288r:2) 0 at 96r 1
at 112r 2 at 208r L00000002 [96r,96d:1)[112r,288r:0) 0 at 112r 1 at 96r
L00000030 [208r,288r:1) 0 at x 1 at 208r L00000001 [96r,288r:0) 0 at 96r
merge %vreg13:2 at 208r into %vreg34:0 at 160r --> @160r
LHST = %vreg13 %vreg13 [96r,112r:0)[112r,208r:1)[208r,288r:2) 0
at 96r 1 at 112r 2 at 208r L00000002 [96r,96d:1)[112r,288r:0) 0 at 112r 1 at
96r L00000030 [208r,288r:1) 0 at x 1 at 208r L00000001 [96r,288r:0) 0 at 96r
Copy+Merge 00000030 into 00000020
Reduce Lane to 00000010
conflict at %vreg34:1 at 240r
*** Couldn't join subrange!
UNREACHABLE executed at
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2693!
#0 0x00000000027395af llvm::sys::PrintStackTrace(llvm::raw_ostream&)
/d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:402:0
#1 0x0000000002739971 PrintStackTraceSignalHandler(void*)
/d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:466:0
#2 0x0000000002737bce llvm::sys::RunSignalHandlers()
/d/en/johnsoni-0/gctools/llvm/lib/Support/Signals.cpp:44:0
#3 0x0000000002738f41 SignalHandler(int)
/d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:256:0
#4 0x000000396140f7e0 __restore_rt (/lib64/libpthread.so.0+0x396140f7e0)
#5 0x0000003960c325e5 __GI_raise (/lib64/libc.so.6+0x3960c325e5)
#6 0x0000003960c33dc5 __GI_abort (/lib64/libc.so.6+0x3960c33dc5)
#7 0x00000000026d4c42 bindingsErrorHandler(void*, std::string const&, bool)
/d/en/johnsoni-0/gctools/llvm/lib/Support/ErrorHandling.cpp:127:0
#8 0x0000000001fdbc85 (anonymous
namespace)::RegisterCoalescer::joinSubRegRanges(llvm::LiveRange&,
llvm::LiveRange&, llvm::LaneBitmask, llvm::CoalescerPair const&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2695:0
#9 0x0000000001fdc3df (anonymous
namespace)::RegisterCoalescer::mergeSubRangeInto(llvm::LiveInterval&,
llvm::LiveRange const&, llvm::LaneBitmask, llvm::CoalescerPair&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2769:0
#10 0x0000000001fdcbd5 (anonymous
namespace)::RegisterCoalescer::joinVirtRegs(llvm::CoalescerPair&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2832:0
#11 0x0000000001fdd174 (anonymous
namespace)::RegisterCoalescer::joinIntervals(llvm::CoalescerPair&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2892:0
#12 0x0000000001fd5fc3 (anonymous
namespace)::RegisterCoalescer::joinCopy(llvm::MachineInstr*, bool&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:1468:0
#13 0x0000000001fdd4b6 (anonymous
namespace)::RegisterCoalescer::copyCoalesceWorkList(llvm::MutableArrayRef<llvm::MachineInstr*>)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2962:0
#14 0x0000000001fddf32 (anonymous
namespace)::RegisterCoalescer::coalesceLocals()
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3087:0
#15 0x0000000001fde3a1 (anonymous
namespace)::RegisterCoalescer::joinAllIntervals()
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3121:0
#16 0x0000000001fde6e2 (anonymous
namespace)::RegisterCoalescer::runOnMachineFunction(llvm::MachineFunction&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3167:0
#17 0x0000000001d28d87
llvm::MachineFunctionPass::runOnFunction(llvm::Function&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/MachineFunctionPass.cpp:62:0
...
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Johnson, Nicholas Paul via llvm-dev
2017-Apr-24 20:21 UTC
[llvm-dev] Debugging UNREACHABLE "Couldn't join subrange" in RegisterCoalescer (out-of-tree backend)
I filed this under http://llvm.org/PR32773
Nick Johnson
D. E. Shaw Research
From: Johnson, Nicholas Paul
Sent: Monday, April 24, 2017 1:14 PM
To: 'mbraun at apple.com'
Cc: llvm-dev at lists.llvm.org
Subject: RE: [llvm-dev] Debugging UNREACHABLE "Couldn't join
subrange" in RegisterCoalescer (out-of-tree backend)
Thank you Matthias,
$ llc bugpoint-reduced-simplified.bc -verify-machineinstrs -debug-only=regalloc
-print-before-all 2>log
Result file 'log' is attached. None of the target-specific instructions
(LI, VEXT, BLT, J) do anything weird with registers.
I saw PR32688, but it looks like a different assertion failing.
One thing that struck me as odd was that RegisterCoalescer::joinVirtRegs
features this guard that looks very similar to the failed condition
// Some conflicts can only be resolved after all values have been mapped.
if (!LHSVals.resolveConflicts(RHSVals) || !RHSVals.resolveConflicts(LHSVals))
return false;
Compare that to the failed condition in RegisterCoalescer::joinSubRegRanges,
which is structurally quite similar but operates on (I think) sub-ranges of
those intervals previously tested.
if (!LHSVals.resolveConflicts(RHSVals) ||
!RHSVals.resolveConflicts(LHSVals)) {
// We already determined that it is legal to merge the intervals, so this
// should never fail.
llvm_unreachable("*** Couldn't join subrange!\n");
}
Nick Johnson
D. E. Shaw Research
From: mbraun at apple.com<mailto:mbraun at apple.com> [mailto:mbraun at
apple.com]
Sent: Monday, April 24, 2017 12:58 PM
To: Johnson, Nicholas Paul
Cc: llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Debugging UNREACHABLE "Couldn't join
subrange" in RegisterCoalescer (out-of-tree backend)
This looks like a bug related to the subregister liveness updating in the
RegisterCoalescer.
As this is always hard to debug without having the actual target at hand:
- Make sure the testcase (or rather all testcases) passes `llc
-verify-machineinstrs`
- It would be good to see the full `llc -debug-only=regalloc` dump (looking
below I would at least see which slotindexes belong to which instructions). Best
to file a PR with the information.
- There is one open PR about coalescing subregister liveness right now:
http://llvm.org/PR32688 (but it's hard to say without investigation whether
it is the same).
- Matthias
On Apr 24, 2017, at 9:10 AM, Johnson, Nicholas Paul via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Hello,
I have a minimal testcase which crashes RegisterCoalescer in my out-of-tree
target. It only crashes in Debug builds of llc---not in Release builds. Also,
interesting to note that the x86 backend lowers this same testcase successfully.
I did a quick search of bugs.llvm.org<http://bugs.llvm.org> and found no
matches.
This implies that the problem is in my backend and/or how my backend interacts
with RegisterCoalescer. I'm not too familiar with RegisterCoalescer. Can
anyone give me a hint on where I should start looking for the problem in my
backend?
Thank you,
Nick Johnson
D. E. Shaw Research
Here's my minimal testcase:
$ llvm-dis -o - bugpoint.reduced.simplified.bc
; ModuleID = 'bugpoint.reduced.simplified.bc'
source_filename = "bugpoint-output-7eb0c3b.bc"
target datalayout =
"e-m:e-p:32:32-i8:8:32-i16:16:32-i32:32:32-i64:64:64-v64:64:64-v128:128:128-n32-S128"
target triple = "desgcv3-unknown-elf"
; Function Attrs: noreturn nounwind
define void @wobble() local_unnamed_addr #0 {
%1 = extractelement <4 x i32> <i32 0, i32 2, i32 3, i32 4>, i32
undef
%2 = sub nsw i32 0, %1
%3 = icmp sgt i32 %2, 0
br i1 %3, label %4, label %5
; <label>:4: ; preds = %5, %0
unreachable
; <label>:5: ; preds = %0
%6 = extractelement <4 x i32> <i32 0, i32 2, i32 3, i32 4>, i32
undef
%7 = sub nsw i32 0, %6
%8 = icmp sgt i32 %7, 0
br i1 %8, label %9, label %4
; <label>:9: ; preds = %5
unreachable
}
attributes #0 = { noreturn nounwind
"correctly-rounded-divide-sqrt-fp-math"="false"
"disable-tail-calls"="false"
"less-precise-fpmad"="false"
"no-frame-pointer-elim"="true"
"no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false"
"no-jump-tables"="false"
"no-nans-fp-math"="false"
"no-signed-zeros-fp-math"="false"
"no-trapping-math"="false"
"stack-protector-buffer-size"="8"
"target-cpu"="generic"
"unsafe-fp-math"="false"
"use-soft-float"="false" }
Here's the tail-end of the log, with debugging turned on:
$llc bugpoint.reduced.simplified.bc -debug
...
208B %vreg13:sub_64_1<def> = COPY %vreg34:sub_64_1;
VecRegs:%vreg13,%vreg34
Considering merging to VecRegs with %vreg34 in %vreg13
RHS = %vreg34
[160r,240r:0)[240r,384B:1)[400B,480r:1)[480r,496r:2)[496r,672r:3) 0 at 160r 1
at 240r 2 at 480r 3 at 496r L00000020 [240r,384B:1)[400B,672r:1) 0 at x 1 at
240r L00000010 [160r,384B:1)[400B,672r:1) 0 at x 1 at 160r L00000002
[480r,480d:1)[496r,672r:0) 0 at 496r 1 at 480r L00000001 [480r,672r:0) 0 at
480r
LHS = %vreg13 [96r,112r:0)[112r,208r:1)[208r,288r:2) 0 at 96r 1
at 112r 2 at 208r L00000002 [96r,96d:1)[112r,288r:0) 0 at 112r 1 at 96r
L00000030 [208r,288r:1) 0 at x 1 at 208r L00000001 [96r,288r:0) 0 at 96r
merge %vreg13:2 at 208r into %vreg34:0 at 160r --> @160r
LHST = %vreg13 %vreg13 [96r,112r:0)[112r,208r:1)[208r,288r:2) 0
at 96r 1 at 112r 2 at 208r L00000002 [96r,96d:1)[112r,288r:0) 0 at 112r 1 at
96r L00000030 [208r,288r:1) 0 at x 1 at 208r L00000001 [96r,288r:0) 0 at 96r
Copy+Merge 00000030 into 00000020
Reduce Lane to 00000010
conflict at %vreg34:1 at 240r
*** Couldn't join subrange!
UNREACHABLE executed at
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2693!
#0 0x00000000027395af llvm::sys::PrintStackTrace(llvm::raw_ostream&)
/d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:402:0
#1 0x0000000002739971 PrintStackTraceSignalHandler(void*)
/d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:466:0
#2 0x0000000002737bce llvm::sys::RunSignalHandlers()
/d/en/johnsoni-0/gctools/llvm/lib/Support/Signals.cpp:44:0
#3 0x0000000002738f41 SignalHandler(int)
/d/en/johnsoni-0/gctools/llvm/lib/Support/Unix/Signals.inc:256:0
#4 0x000000396140f7e0 __restore_rt (/lib64/libpthread.so.0+0x396140f7e0)
#5 0x0000003960c325e5 __GI_raise (/lib64/libc.so.6+0x3960c325e5)
#6 0x0000003960c33dc5 __GI_abort (/lib64/libc.so.6+0x3960c33dc5)
#7 0x00000000026d4c42 bindingsErrorHandler(void*, std::string const&, bool)
/d/en/johnsoni-0/gctools/llvm/lib/Support/ErrorHandling.cpp:127:0
#8 0x0000000001fdbc85 (anonymous
namespace)::RegisterCoalescer::joinSubRegRanges(llvm::LiveRange&,
llvm::LiveRange&, llvm::LaneBitmask, llvm::CoalescerPair const&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2695:0
#9 0x0000000001fdc3df (anonymous
namespace)::RegisterCoalescer::mergeSubRangeInto(llvm::LiveInterval&,
llvm::LiveRange const&, llvm::LaneBitmask, llvm::CoalescerPair&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2769:0
#10 0x0000000001fdcbd5 (anonymous
namespace)::RegisterCoalescer::joinVirtRegs(llvm::CoalescerPair&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2832:0
#11 0x0000000001fdd174 (anonymous
namespace)::RegisterCoalescer::joinIntervals(llvm::CoalescerPair&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2892:0
#12 0x0000000001fd5fc3 (anonymous
namespace)::RegisterCoalescer::joinCopy(llvm::MachineInstr*, bool&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:1468:0
#13 0x0000000001fdd4b6 (anonymous
namespace)::RegisterCoalescer::copyCoalesceWorkList(llvm::MutableArrayRef<llvm::MachineInstr*>)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:2962:0
#14 0x0000000001fddf32 (anonymous
namespace)::RegisterCoalescer::coalesceLocals()
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3087:0
#15 0x0000000001fde3a1 (anonymous
namespace)::RegisterCoalescer::joinAllIntervals()
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3121:0
#16 0x0000000001fde6e2 (anonymous
namespace)::RegisterCoalescer::runOnMachineFunction(llvm::MachineFunction&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/RegisterCoalescer.cpp:3167:0
#17 0x0000000001d28d87
llvm::MachineFunctionPass::runOnFunction(llvm::Function&)
/d/en/johnsoni-0/gctools/llvm/lib/CodeGen/MachineFunctionPass.cpp:62:0
...
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