[PATCH] D135693: [WIP][RegisterScavenger][RISCV] Don't search for FrameSetup instrs if we were searching from Non-FrameSetup instrs

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

In D135693#3851366 <https://reviews.llvm.org/D135693#3851366>, @StephenFan wrote:

> In D135693#3850538 <https://reviews.llvm.org/D135693#3850538>, @craig.topper wrote:
>
>> In D135693#3850055 <https://reviews.llvm.org/D135693#3850055>, @craig.topper wrote:
>>
>>> If I understand correctly, the use of a vreg in the frame-setup allowed findSurvivorBackward to trigger this code
>>>
>>>   // Keep searching when we find a vreg since the spilled register will
>>>   // be usefull for this other vreg as well later.
>>>   bool FoundVReg = false;
>>>   for (const MachineOperand &MO : MI.operands()) {
>>>     if (MO.isReg() && Register::isVirtualRegister(MO.getReg())) {
>>>       FoundVReg = true;
>>>       break;
>>>     }
>>>   }
>>>   if (FoundVReg) {
>>>     InstrCountDown = InstrLimit;
>>>     Pos = I;
>>>   }
>>>
>>> which caused the search to stop above the frame-setup. So another option might be to use T1 as the scratch register in frame-setup as was once proposed in an earlier revision of https://reviews.llvm.org/D61884
>>
>> But we can't use T1 with shrink wrapping and I've confirmed the same bug exists with shrink wrapping.
>
> Thanks for looking into shrink-wrapping! Do you mind sharing your shrink-wrapping test cases? So that I can pick them as CodeGen/RISCV test cases.

This was my shrink wrap case

  @var = external global i32                                                       
                                                                                   
  define void @func(i1 %c) {                                                       
    %space = alloca i32, align 4                                                   
    %stackspace = alloca[1024 x i32], align 4                                      
    br i1 %c, label %foo, label %bar                                               
                                                                                   
  bar:                                                                             
                                                                                   
    ;; Load values to increase register pressure.                                  
    %v0 = load volatile i32, i32* @var                                             
    %v1 = load volatile i32, i32* @var                                             
    %v2 = load volatile i32, i32* @var                                             
    %v3 = load volatile i32, i32* @var                                             
    %v4 = load volatile i32, i32* @var                                             
    %v5 = load volatile i32, i32* @var                                             
    %v6 = load volatile i32, i32* @var                                             
    %v7 = load volatile i32, i32* @var                                             
    %v8 = load volatile i32, i32* @var                                             
    %v9 = load volatile i32, i32* @var                                             
    %v10 = load volatile i32, i32* @var                                            
    %v11 = load volatile i32, i32* @var                                            
    %v12 = load volatile i32, i32* @var                                            
    %v13 = load volatile i32, i32* @var                                            
                                                                                   
    store volatile i32 %v0, i32* %space                                            
                                                                                   
    ;; store values so they are used.                                              
    store volatile i32 %v0, i32* @var                                              
    store volatile i32 %v1, i32* @var                                              
    store volatile i32 %v2, i32* @var                                              
    store volatile i32 %v3, i32* @var                                              
    store volatile i32 %v4, i32* @var                                              
    store volatile i32 %v5, i32* @var                                              
    store volatile i32 %v6, i32* @var                                              
    store volatile i32 %v7, i32* @var                                              
    store volatile i32 %v8, i32* @var                                              
    store volatile i32 %v9, i32* @var                                              
    store volatile i32 %v10, i32* @var                                             
    store volatile i32 %v11, i32* @var                                             
    store volatile i32 %v12, i32* @var                                             
    store volatile i32 %v13, i32* @var                                             
    br label %foo                                                                  
                                                                                   
  foo:                                                                             
    ret void                                                                       
  }       


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