[PATCH] D84589: [CodeMoverUtils] Add optional data dependence checks using Alias Analysis

[Bardia Mahjour via Phabricator via llvm-commits]

bmahjour added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/CodeMoverUtils.cpp:250
+  if (CallInst *CI = dyn_cast<CallInst>(&I)) {
+    for (Value *Op : CI->arg_operands())
+      if (Op->getType()->isPointerTy()) {
----------------
RithikSharma wrote:
> bmahjour wrote:
> > I think the call itself should also go into the MemLocs vector.
> CallInst returns none memory location, which won't be useful to find dependence info and we may have to skip it so I did not add it into the MemLocs in the first place. 
Then we have a problem if the memory accesses of a function are not represented through their arguments. For example consider:
```
int a = 0;

void foo() {
  a = 1;
}

int main() {
  foo();
  a = 3;
  return a;
}
```
In the case above `a = 3` should not be allowed to move before the call to `foo()`.

If this information is not available through AliasAnalysis, then we have to check for it separately. One way to solve it is to look at the underlying object referenced by `I` and `Inst`, and if any of them is a global and one of the intervening instructions is a call that may have side-effect, then return false. 


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D84589/new/

https://reviews.llvm.org/D84589