Assertion "LowerFormalArguments didn't emit the correct number of values!" failed

[gergoerdi]

target triple = "avr-atmel-none"

; Function Attrs: norecurse nounwind readonly uwtable
define i128 @"_ZN43_$LT$i32$u20$as$u20$core..fmt..num..Int$GT$7to_u12817haa6ed143bf6636caE"(i32* noalias nocapture readonly dereferenceable(4)) unnamed_addr #6 {
start:
  %1 = load i32, i32* %0, align 4
  %2 = sext i32 %1 to i128
  ret i128 %2
}

EDIT (@dylanmckay): Here is another reproduction caused with non-i128 types. This was originally raised on #89. We should double check whatever fix is made fixes both of these.

declare i8 @do_something(i8 %val)

define { i1, i8 } @main(i8) #2 {
entry:
  %1 = call zeroext i8 @do_something(i8 zeroext %0)
  %2 = insertvalue { i1, i8 } { i1 true, i8 undef }, i8 %1, 1
  ret { i1, i8 } %2
}

CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:8143: void llvm::SelectionDAGISel::LowerArguments(const llvm::Function&): Assertion `InVals.size() == Ins.size() && "LowerFormalArguments didn't emit the correct number of values!"' failed.
#0 0x0000000001721085 llvm::sys::PrintStackTrace(llvm::raw_ostream&) (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x1721085)
#1 0x000000000171f09e llvm::sys::RunSignalHandlers() (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x171f09e)
#2 0x000000000171f202 SignalHandler(int) (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x171f202)
#3 0x00007fa62aaf3330 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x10330)
#4 0x00007fa629cafc37 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x36c37)
#5 0x00007fa629cb3028 abort (/lib/x86_64-linux-gnu/libc.so.6+0x3a028)
#6 0x00007fa629ca8bf6 (/lib/x86_64-linux-gnu/libc.so.6+0x2fbf6)
#7 0x00007fa629ca8ca2 (/lib/x86_64-linux-gnu/libc.so.6+0x2fca2)
#8 0x00000000015c0f83 llvm::SelectionDAGISel::LowerArguments(llvm::Function const&) (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x15c0f83)
#9 0x00000000016091cc llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x16091cc)
#10 0x000000000160ac3c llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) [clone .part.948] (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x160ac3c)
#11 0x00000000010e8523 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x10e8523)
#12 0x000000000138ba03 llvm::FPPassManager::runOnFunction(llvm::Function&) (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x138ba03)
#13 0x000000000138baac llvm::FPPassManager::runOnModule(llvm::Module&) (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x138baac)
#14 0x000000000138c80f llvm::legacy::PassManagerImpl::run(llvm::Module&) (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x138c80f)
#15 0x0000000000697f74 compileModule(char**, llvm::LLVMContext&) (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x697f74)
#16 0x0000000000646a90 main (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x646a90)
#17 0x00007fa629c9af45 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21f45)
#18 0x000000000068d2b5 _start (/home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc+0x68d2b5)

Stack dump:
0.	Program arguments: /home/cactus/prog/rust/rust-avr/build/build/x86_64-unknown-linux-gnu/llvm/bin/llc -mcpu=atmega328p a.ll 
1.	Running pass 'Function Pass Manager' on module 'a.ll'.
2.	Running pass 'AVR DAG->DAG Instruction Selection' on function '@"_ZN43_$LT$i32$u20$as$u20$core..fmt..num..Int$GT$7to_u12817haa6ed143bf6636caE"'

[dylanmckay]

This is occurring because SelectionDAGISel::LowerArguments notices that FuncInfo->CanLowerReturn is false and so it attempts to convert the return value into an argument.

For some reason, our LowerFormalArguments is not doing what it should be in this case.

I can verify that this is causing it because if I add more registers to the calling convention

  def RetCC_AVR : CallingConv
  <[
    // i8 is returned in R24.
    CCIfType<[i8], CCAssignToReg<[R24]>>,

    // i16 are returned in R25:R24, R23:R22, R21:R20 and R19:R18.
    CCIfType<[i16], CCAssignToReg<[R25R24, R23R22, R21R20, R19R18, R17R16, R15R14, R13R12, R11R10]>>
  ]>;

It compiles successfully.

[dylanmckay]

I think we're missing something like this (taken from MipsISelLowering.cpp)

  for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i) {
    // The mips ABIs for returning structs by value requires that we copy
    // the sret argument into $v0 for the return. Save the argument into
    // a virtual register so that we can access it from the return points.
    if (Ins[i].Flags.isSRet()) {
      unsigned Reg = MipsFI->getSRetReturnReg();
      if (!Reg) {
        Reg = MF.getRegInfo().createVirtualRegister(
            getRegClassFor(ABI.IsN64() ? MVT::i64 : MVT::i32));
        MipsFI->setSRetReturnReg(Reg);
      }
      SDValue Copy = DAG.getCopyToReg(DAG.getEntryNode(), DL, Reg, InVals[i]);
      Chain = DAG.getNode(ISD::TokenFactor, DL, MVT::Other, Copy, Chain);
      break;
    }
  }

[dylanmckay]

I think this is not actually it, it's just something similar.

[dylanmckay]

It's strange that there's an extra argument for the return value, but analyzeArguments is only populating ArgLocs with one element.

[dylanmckay]

It looks like our parseFunctionArgs method is directly reading the arguments from a Function object, and not the arguments supplied by the SelectionDAGBuilder - this will be why we are only lowering one argument but not two.

[dylanmckay]

Have pushed to a WIP patch avr-rust/llvm/branches/issue-57

Fixing the bug triggers another bug in add.ll and a bunch of other tests.