Assertion `TFI->hasReservedCallFrame(MF) && "Cannot use SP to access the emergency spill slot in " "functions without a reserved call frame"' failed.

[thevinster]

I'm debugging a crash that's happening in the Prologue/Epilogue Insertion & Frame Finalization backend with an assertion failure of the following:

virtual bool llvm::ARMBaseRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator, int, unsigned int, RegScavenger *) const: Assertion `TFI->hasReservedCallFrame(MF) && "Cannot use SP to access the emergency spill slot in " "functions without a reserved call frame"' failed.

I'm able to reduce the crash to this IR (Godbolt:https://godbolt.org/z/nrrd33YPW). Running llc on this file with -O0 on this input crashes on both LLVM main and on release/18.x.

[llvmbot]

@llvm/issue-subscribers-backend-arm

Author: Vincent Lee (thevinster)

I'm debugging a crash that's happening in the Prologue/Epilogue Insertion & Frame Finalization backend with an assertion failure of the following: ``` virtual bool llvm::ARMBaseRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator, int, unsigned int, RegScavenger *) const: Assertion `TFI->hasReservedCallFrame(MF) && "Cannot use SP to access the emergency spill slot in " "functions without a reserved call frame"' failed. ```

I'm able to reduce the crash to this IR. Running llc on this file with -O0 on this input crashes on both LLVM main and on release/18.x.

[MatzeB]

At a first glance, the issue here seems to be that ARMFrameLowering::determineCalleeSaves decides that the function does not need a frame pointer.

Specifically there is a bool HasLargeStack = EstimatedStackSize > EstimatedRSStackSizeLimit; condition that is not triggering but probably should for this function. In a debugger I see EstimatedStackSize == 244, EstimatedRSStackSizeLimit==4095. It seems like EstimatedStackSize which is supposed to be equal or bigger than the real stack size is missing the call-frame and/or all the stores necessary for parameter passing here which I can see to go up to t2STRi12 renamable $r12, renamable $r0, 4076 in MIR..

(thought not 100% sure yet whether it some of the other conditions around this functions are supposed to trigger instead...)