[PATCH] D109170: [Attributor] Look through allocated heap memory

[Kuter Dinel via Phabricator via llvm-commits]

kuter added a comment.

Note: Some tests seem broken (heap_to_stack.ll)  and clang format is needed.

Also, do you think we can optimize nested stuff ? for example if a pointer was stored to memory.
I think `checkForAllUses` can look through values that escape to memory,  right ?



================
Comment at: llvm/lib/Transforms/IPO/Attributor.cpp:210
     return UndefValue::get(&Ty);
+  if (isNoAliasFn(&Obj, TLI)) {
+    if (isMallocLikeFn(&Obj, TLI) || isAlignedAllocLikeFn(&Obj, TLI))
----------------
I don't think this check is needed.  `isNoAliasFn` seems to always return true if this is a allocation function.

Source code for `isNoAliasFn`
```
 /// Tests if a value is a call or invoke to a function that returns a
 /// NoAlias pointer (including malloc/calloc/realloc/strdup-like functions).
 bool llvm::isNoAliasFn(const Value *V, const TargetLibraryInfo *TLI,
                        bool LookThroughBitCast) {
   // it's safe to consider realloc as noalias since accessing the original
   // pointer is undefined behavior
   return isAllocationFn(V, TLI, LookThroughBitCast) ||
          hasNoAliasAttr(V, LookThroughBitCast);
 }
```



================
Comment at: llvm/lib/Transforms/IPO/AttributorAttributes.cpp:2344
     AANoRecurseImpl::initialize(A);
+    // TODO: We should build a call graph ourselves to enable this in the module pass as well.
     if (const Function *F = getAnchorScope())
----------------
Do you think we should use the `AAReachability` here ? 
If the function can reach itself, then it is recursive. 


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109170/new/

https://reviews.llvm.org/D109170