[PATCH] D60793: [Evaluator] Walk initial elements when handling load through bitcast

[Robert Lougher via Phabricator via llvm-commits]

rob.lougher added a comment.

In D60793#1470376 <https://reviews.llvm.org/D60793#1470376>, @evgeny777 wrote:

> > "MutatedMemory" is only used to hold evaluated store values
>
> It is also used to patch initializers - see `BatchCommitValueTo`


With values from evaluated stores.

>> Using the bitcast as a key would be dangerous
> 
> There is no straightforward way to do this in `MutatedMemory` because GEP is a special key type (see BatchCommitValueTo)
>  That's why I suggested using another map.
> 
>> we could then get different values for the same memory location
> 
> How?

  union A {
    float f;
    int i;
  };
  
  void s1(union A *u) {
    u->i = 123;
  }
  
  void s2(union A *u) {
    u->f = 1.23;
  }
  
  int foo() {
    union A u;
    s1(&u);
    s2(&u);
    return u.i;
  }
  
  int i = foo();

Input to Global Var  Opt:

  define dso_local void @_Z2s1P1A(%union.A* %u) #0 {
    %i = bitcast %union.A* %u to i32*
    store i32 123, i32* %i, align 4, !tbaa !2
    ret void
  }
  
  define dso_local void @_Z2s2P1A(%union.A* %u) #0 {
    %f = bitcast %union.A* %u to float*
    store float 0x3FF3AE1480000000, float* %f, align 4, !tbaa !2
    ret void
  }
  
  define dso_local i32 @_Z3foov() #0 {
    %u = alloca %union.A, align 4
    %0 = bitcast %union.A* %u to i8*
    call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #3
    call void @_Z2s1P1A(%union.A* %u)
    call void @_Z2s2P1A(%union.A* %u)
    %i = bitcast %union.A* %u to i32*
    %1 = load i32, i32* %i, align 4, !tbaa !2
    call void @llvm.lifetime.end.p0i8(i64 4, i8* %0) #3
    ret i32 %1
  }

Currently both store bitcasts will be replaced by a GEP to the first element, which means the load will get the correct value.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D60793/new/

https://reviews.llvm.org/D60793