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[WebAssembly] stacksave leads machine code verification failure after wasm-replace-phys-regs #62235

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kateinoigakukun opened this issue Apr 19, 2023 · 1 comment · Fixed by #68133
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[WebAssembly] stacksave leads machine code verification failure after wasm-replace-phys-regs #62235

kateinoigakukun opened this issue Apr 19, 2023 · 1 comment · Fixed by #68133
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backend:WebAssembly llvm:codegen

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@kateinoigakukun
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kateinoigakukun commented Apr 19, 2023 •
edited by VoltrexKeyva
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LLVM version: llvmorg-16.0.0

Minimum reproducible code:

target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128-ni:1:10:20"
target triple = "wasm32-unknown-wasi"

define weak_odr swiftcc { i32, i8 } @x(i1 %0) {
entry:
  br i1 %0, label %.thread51, label %.lr.ph.i30

.thread51:                                        ; preds = %entry
  %spsave253 = tail call i8* @llvm.stacksave()
  br label %.loopexit

.lr.ph.i30:                                       ; preds = %.lr.ph.i30, %entry
  br i1 %0, label %.loopexit, label %.lr.ph.i30

.loopexit:                                        ; preds = %.lr.ph.i30, %.thread51
  %spsave254.ph = phi i8* [ %spsave253, %.thread51 ], [ null, %.lr.ph.i30 ]
  tail call void @llvm.stackrestore(i8* %spsave254.ph)
  unreachable
}

; Function Attrs: nocallback nofree nosync nounwind willreturn
declare i8* @llvm.stacksave() #0

; Function Attrs: nocallback nofree nosync nounwind willreturn
declare void @llvm.stackrestore(i8*) #0

attributes #0 = { nocallback nofree nosync nounwind willreturn }
$ llc test.ll -stop-after wasm-replace-phys-regs -o - -verify-machineinstrs
# Machine code for function x: NoPHIs, TracksLiveness, TiedOpsRewritten
Function Live Ins: $arguments

bb.0.entry:
  successors: %bb.1(0x00000000), %bb.2(0x80000000); %bb.1(0.00%), %bb.2(100.00%)
  liveins: $arguments
  %3:i32 = ARGUMENT_i32 1, implicit $arguments
  dead %2:i32 = ARGUMENT_i32 0, implicit $arguments
  %4:i32 = CONST_I32 1, implicit-def dead $arguments
  %5:i32 = AND_I32 %3:i32, %4:i32, implicit-def dead $arguments
  BR_UNLESS %bb.2, %5:i32, implicit-def $arguments

bb.1..thread51:
; predecessors: %bb.0

  %10:i32 = COPY_I32 %11:i32, implicit-def $arguments
  %11:i32 = COPY_I32 %10:i32, implicit-def $arguments
  UNREACHABLE implicit-def dead $arguments

bb.2..lr.ph.i30:
; predecessors: %bb.2, %bb.0
  successors: %bb.3(0x00000000), %bb.2(0x80000000); %bb.3(0.00%), %bb.2(100.00%)

  BR_UNLESS %bb.2, %5:i32, implicit-def dead $arguments

bb.3:
; predecessors: %bb.2

  %10:i32 = CONST_I32 0, implicit-def dead $arguments
  %11:i32 = COPY_I32 %10:i32, implicit-def $arguments
  UNREACHABLE implicit-def dead $arguments

# End machine code for function x.

*** Bad machine code: Virtual register defs don't dominate all uses. ***
- function:    x
- v. register: %11
LLVM ERROR: Found 1 machine code errors.
Stack trace 
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: /home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc Swift.x.wasm32-unknown-wasi.reduced.ll
1.      Running pass 'Function Pass Manager' on module 'Swift.x.wasm32-unknown-wasi.reduced.ll'.
2.      Running pass 'Live Interval Analysis' on function '@x'
 #0 0x0000000001e019d3 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x1e019d3)
 #1 0x0000000001dff6fe llvm::sys::RunSignalHandlers() (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x1dff6fe)
 #2 0x0000000001e01e9f SignalHandler(int) Signals.cpp:0:0
 #3 0x00007f6a7e2c3420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00007f6a7dd5600b raise /build/glibc-SzIz7B/glibc-2.31/signal/../sysdeps/unix/sysv/linux/raise.c:51:1
 #5 0x00007f6a7dd35859 abort /build/glibc-SzIz7B/glibc-2.31/stdlib/abort.c:81:7
 #6 0x0000000001d7e6b0 llvm::report_fatal_error(llvm::Twine const&, bool) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x1d7e6b0)
 #7 0x000000000127f7a6 (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x127f7a6)
 #8 0x00000000011004aa llvm::LiveRangeCalc::findReachingDefs(llvm::LiveRange&, llvm::MachineBasicBlock&, llvm::SlotIndex, unsigned int, llvm::ArrayRef<llvm::SlotIndex>) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x11004aa)
 #9 0x00000000010ff7f7 llvm::LiveRangeCalc::extend(llvm::LiveRange&, llvm::SlotIndex, unsigned int, llvm::ArrayRef<llvm::SlotIndex>) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x10ff7f7)
#10 0x000000000110321a llvm::LiveIntervalCalc::extendToUses(llvm::LiveRange&, llvm::Register, llvm::LaneBitmask, llvm::LiveInterval*) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x110321a)
#11 0x0000000001102ec0 llvm::LiveIntervalCalc::calculate(llvm::LiveInterval&, bool) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x1102ec0)
#12 0x00000000010ead22 llvm::LiveIntervals::computeVirtRegInterval(llvm::LiveInterval&) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x10ead22)
#13 0x00000000010e9824 llvm::LiveIntervals::computeVirtRegs() (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x10e9824)
#14 0x00000000010e95f2 llvm::LiveIntervals::runOnMachineFunction(llvm::MachineFunction&) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x10e95f2)
#15 0x00000000011a4641 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x11a4641)
#16 0x000000000165c868 llvm::FPPassManager::runOnFunction(llvm::Function&) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x165c868)
#17 0x0000000001664f41 llvm::FPPassManager::runOnModule(llvm::Module&) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x1664f41)
#18 0x000000000165d034 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x165d034)
#19 0x00000000006e3a7d compileModule(char**, llvm::LLVMContext&) llc.cpp:0:0
#20 0x00000000006e144d main (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x6e144d)
#21 0x00007f6a7dd37083 __libc_start_main /build/glibc-SzIz7B/glibc-2.31/csu/../csu/libc-start.c:342:3
#22 0x00000000006e07ae _start (/home/katei/ghq/work.katei.dev/swiftwasm-source/host-build/Ninja-ReleaseAssert/llvm-linux-x86_64/bin/llc+0x6e07ae)

It looks like $sp32 read by stacksave is replaced with a virtual reg by wasm-replace-phys-regs, but it results in violating the domination principle for virtual registers.

Result of `-stop-before=wasm-replace-phys-regs` 
  bb.0.entry:
    successors: %bb.1(0x00000000), %bb.2(0x80000000)
    liveins: $arguments

    %3:i32 = ARGUMENT_i32 1, implicit $arguments
    dead %2:i32 = ARGUMENT_i32 0, implicit $arguments
    %4:i32 = CONST_I32 1, implicit-def dead $arguments
    %5:i32 = AND_I32 %3, %4, implicit-def dead $arguments
    BR_UNLESS %bb.2, %5, implicit-def $arguments

  bb.1..thread51:
    %10:i32 = COPY_I32 $sp32, implicit-def $arguments
    $sp32 = COPY_I32 %10, implicit-def $arguments
    UNREACHABLE implicit-def dead $arguments

  bb.2..lr.ph.i30:
    successors: %bb.3(0x00000000), %bb.2(0x80000000)

    BR_UNLESS %bb.2, %5, implicit-def dead $arguments

  bb.3:
    %10:i32 = CONST_I32 0, implicit-def dead $arguments
    $sp32 = COPY_I32 %10, implicit-def $arguments
    UNREACHABLE implicit-def dead $arguments

I'm not sure the stacksave / stackrestore are supported on WebAssembly target or not 🤷 But it seems that it somehow succeeds with LLVM 14: https://godbolt.org/z/7Mx45GqK6
@llvmbot
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llvmbot commented Apr 19, 2023

@llvm/issue-subscribers-backend-webassembly

@kateinoigakukun kateinoigakukun changed the title WebAssembly: stacksave leads machine code verification failure after wasm-replace-phys-regs [WebAssembly] stacksave leads machine code verification failure after wasm-replace-phys-regs Apr 19, 2023
kateinoigakukun added a commit to kateinoigakukun/swift that referenced this issue Sep 14, 2023
@kateinoigakukun
[wasm][stdlib] HACK: Workaround for the bad stacksave codegen in LLVM
ebe32fa 
The LLVM backend generates bad code for some code using `llvm.stacksave`
intrinsics. This patch works around the issue by avoiding such code
generation. See llvm/llvm-project#62235
@kateinoigakukun kateinoigakukun mentioned this issue Oct 3, 2023
Merged
dschuff pushed a commit that referenced this issue Oct 3, 2023
@kateinoigakukun
[WebAssembly] Define local sp if llvm.stacksave is used (#68133)
da0ca5d 
Usually `llvm.stacksave/stackrestore` are used together with `alloca`
but they can appear without it (e.g. `alloca` can be optimized away).
WebAssembly's function local physical user sp register, which is
referenced by `llvm.stacksave` is created while frame lowering and
replaced with virtual register.
However the sp register was not created when `llvm.stacksave` is used
without `alloca`, and it led MIR verification failure about
use-before-def of sp virtual register.

Resolves #62235
kateinoigakukun added a commit to swiftlang/llvm-project that referenced this issue Oct 9, 2023
@kateinoigakukun
[WebAssembly] Define local sp if llvm.stacksave is used (llvm#68133)
44efb09 
Usually `llvm.stacksave/stackrestore` are used together with `alloca`
but they can appear without it (e.g. `alloca` can be optimized away).
WebAssembly's function local physical user sp register, which is
referenced by `llvm.stacksave` is created while frame lowering and
replaced with virtual register.
However the sp register was not created when `llvm.stacksave` is used
without `alloca`, and it led MIR verification failure about
use-before-def of sp virtual register.

Resolves llvm#62235
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[WebAssembly] Define local sp if llvm.stacksave is used kateinoigakukun/llvm-project
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