Assertion `BestRC && "Couldn't find the register class"

[llvmbot]

Bugzilla Link	11314
Resolution	FIXED
Resolved on	Nov 10, 2011 01:45
Version	trunk
OS	Linux
Attachments	reproducer, minimal reproducer
Reporter	LLVM Bugzilla Contributor
CC	@sunfishcode,@pwo

Extended Description

After r143660, the attached bitcode triggers an assertion when compiled with:

$ llc -march=x86 -mcpu=pentium4 -mtriple=i686-none-linux bug.ll

llvm/lib/Target/TargetRegisterInfo.cpp:68: const llvm::TargetRegisterClass* llvm::TargetRegisterInfo::getMinimalPhysRegClass(unsigned int, llvm::EVT) const: Assertion `BestRC && "Couldn't find the register class"' failed.
0 llc 0x0000000000d9a01f
1 llc 0x0000000000d9c292
2 libpthread.so.0 0x00007fdd4a1118f0
3 libc.so.6 0x00007fdd49400a75 gsignal + 53
4 libc.so.6 0x00007fdd494045c0 abort + 384
5 libc.so.6 0x00007fdd493f9941 __assert_fail + 241
6 llc 0x0000000000c3d034 llvm::TargetRegisterInfo::getMinimalPhysRegClass(unsigned int, llvm::EVT) const + 324
7 llc 0x00000000007d67b4
8 llc 0x00000000007d714f
9 llc 0x0000000000a5ad71 llvm::ScheduleDAG::Run(llvm::MachineBasicBlock*, llvm::ilist_iteratorllvm::MachineInstr) + 1617
10 llc 0x0000000000855ebb llvm::SelectionDAGISel::CodeGenAndEmitDAG() + 1403
11 llc 0x0000000000856c9e llvm::SelectionDAGISel::SelectBasicBlock(llvm::ilist_iterator<llvm::Instruction const>, llvm::ilist_iterator<llvm::Instruction const>, bool&) + 270
12 llc 0x0000000000859b19 llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) + 2265
13 llc 0x000000000085f430 llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 1024
14 llc 0x0000000000cf00bb llvm::FPPassManager::runOnFunction(llvm::Function&) + 587
15 llc 0x0000000000cf01a3 llvm::FPPassManager::runOnModule(llvm::Module&) + 51
16 llc 0x0000000000cefbb7 llvm::MPPassManager::runOnModule(llvm::Module&) + 503
17 llc 0x0000000000cefd4b llvm::PassManagerImpl::run(llvm::Module&) + 187
18 llc 0x000000000052f5da main + 4234
19 libc.so.6 0x00007fdd493ebc4d __libc_start_main + 253
20 llc 0x000000000052cb99
Stack dump:
0. Program arguments: llvm-install/bin/llc -march=x86 -mcpu=pentium4 -mtriple=i686-none-linux bug.ll -o bug.s

1. Running pass 'Function Pass Manager' on module 'bug.ll'.
2. Running pass 'X86 DAG->DAG Instruction Selection' on function '@sscanf'

[sunfishcode]

Edges added by AddPseudoTwoAddrDeps are combining with the new physreg dependence tracking for calls to produce an unschedulable graph. Ideally the scheduler should break the artificial dependence in this case, but it's complicated by the fact that it's hard to identify which edge caused the problem.

[sunfishcode]

Fixed in r144124.

[llvmbot]

... which was reverted. r144267 disabled the scheduler optimization completely.