[PATCH] D57183: [COFF, ARM64] Fix localaddress to handle stack realignment

[Mandeep Singh Grang via Phabricator via llvm-commits]

mgrang added a comment.

In the existing code, there are several conditions on when FP/BP/SP should be used. I have tried to summarize them here:

  use BP:
    if ((hasVarSizedObjects || hasEHFunclets)) && (needsStackRealignment || LocalFrameSize >= 256))
  
  use FP:	
    if (hasEHFunclets || hasVarSizedObjects || needsStackRealignment || hasLocalEscape ||
        hasCalls || isFrameAddressTaken || hasStackMap || hasPatchPoint || !MaxCallFrameSizeComputed ||
        MaxCallFrameSize > DefaultSafeSPDisplacement)
  
  else use SP

Here's my understanding of how the locals should be accessed in various scenarios:

  struct S { int x; };
  
  // Use FP to access escaped locals: (hasFunclets = true, hasVarSizedObjects = false, needsStackRealignment = false)
  void simple() {
    struct S o;
  
    __try { o.x; }
    __finally { o.x; }
  }
  
  // Use BP to access escaped locals: (hasFunclets = true, hasVarSizedObjects = false, needsStackRealignment = true)
  void stack_realignment() {
    struct S __declspec(align(32)) o;
  
    __try { o.x; }
    __finally { o.x; }
  }
  
  // Use BP to access escaped locals: (hasFunclets = true, hasVarSizedObjects = true, needsStackRealignment = false)
  void vla_present(int n) {
    int vla[n];
  
    __try { vla[0]; }
    __finally { vla[0]; }
  }
  
  // Use BP to access escaped locals: (hasFunclets = true, hasVarSizedObjects = true, needsStackRealignment = true)
  void all(int n) {
    struct S __declspec(align(32)) o;
    int vla[n];
    
    __try { o.x; vla[0]; }
    __finally { o.x; vla[0]; }
  }
  
  // Use SP to access locals: (hasFunclets = false, hasVarSizedObjects = false, needsStackRealignment = false)
  void non_seh() {
    // call to llvm.localaddress();
  }

Could you please comment on if all the scenarios have been captured here and if the behavior is what is expected?


Repository:
  rL LLVM

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  https://reviews.llvm.org/D57183/new/

https://reviews.llvm.org/D57183