Segmentation fault in opt with -x86-codegen

Hi All,

We are observing a segmentation fault in opt with -x86-codegen switch. This happens with any general llvm-IR. Please find attached a simple testcase. It can be reproduced with the following.

opt -S -o a.out.ll a.ll -x86-codegen

The traces of the error is as follows.

Stack dump:
0. Program arguments: /home/raghesh/code/mirror/llvm-project/build/bin/opt -S -o a.out.ll a.ll -x86-codegen
#0 0x00007ff5339d728a llvm::sys::PrintStackTrace(llvm::raw_ostream&) (/home/raghesh/code/mirror/llvm-project/build/bin/…/lib/
#1 0x00007ff5339d4f64 llvm::sys::RunSignalHandlers() (/home/raghesh/code/mirror/llvm-project/build/bin/…/lib/
#2 0x00007ff5339d50a2 SignalHandler(int) (/home/raghesh/code/mirror/llvm-project/build/bin/…/lib/
#3 0x00007ff53291ef20 (/lib/x86_64-linux-gnu/
#4 0x00007ff533d86080 llvm::MachineModuleInfo::MachineModuleInfo(llvm::LLVMTargetMachine const*) (/home/raghesh/code/mirror/llvm-project/build/bin/…/lib/
#5 0x00007ff533d86178 llvm::Pass* llvm::callDefaultCtorllvm::MachineModuleInfo() (/home/raghesh/code/mirror/llvm-project/build/bin/…/lib/
#6 0x00007ff533b0c83d llvm::PMTopLevelManager::schedulePass(llvm::Pass*) (/home/raghesh/code/mirror/llvm-project/build/bin/…/lib/
#7 0x00007ff533b0c9a3 llvm::PMTopLevelManager::schedulePass(llvm::Pass*) (/home/raghesh/code/mirror/llvm-project/build/bin/…/lib/
#8 0x0000557729456ac4 main (/home/raghesh/code/mirror/llvm-project/build/bin/opt+0x1dac4)
#9 0x00007ff532901b97 __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/…/csu/libc-start.c:344:0
#10 0x000055772945795a _start (/home/raghesh/code/mirror/llvm-project/build/bin/opt+0x1e95a)
Segmentation fault (core dumped)

With a preliminary analysis, it can be seen that MachineModuleInfo pass which is a “Required” dependency of MachineFunction pass invoked by -x86-codegen.Here, the MachineModuleInfo is created through the call to llvm::callDefaultCtorllvm::MachineModuleInfo(). However, the default constructor of MachineModuleInfo expects a valid pointer to LLVMTargetMachine, which happens to be nullptr in this case and triggers seg fault when accessed.

It would be great if someone could have a look at it and provide or suggest the proper fix.


a.ll (1.65 KB)

That isn’t supposed to work; “x86-codegen” refers to the “X86 FP Stackifier” pass, which only makes sense on MIR, not LLVM IR. We could print a better error message, though: maybe we could add a report_fatal_error to the MachineModuleInfo constructor.