[all-commits] [llvm/llvm-project] 732353: [flang] AliasAnalysis: Fix pointer component logic...

[Joel E. Denny via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 732353303e423237b7d23695a0e516728e491da4
      https://github.com/llvm/llvm-project/commit/732353303e423237b7d23695a0e516728e491da4
  Author: Joel E. Denny <jdenny.ornl at gmail.com>
  Date:   2024-10-15 (Tue, 15 Oct 2024)

  Changed paths:
    M flang/include/flang/Optimizer/Analysis/AliasAnalysis.h
    M flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
    M flang/test/Analysis/AliasAnalysis/alias-analysis-3.fir
    M flang/test/Analysis/AliasAnalysis/ptr-component.fir

  Log Message:
  -----------
  [flang] AliasAnalysis: Fix pointer component logic (#94242)

This PR applies the changes discussed in [[RFC] Rationale for Flang
AliasAnalysis pointer component
logic](https://discourse.llvm.org/t/rfc-rationale-for-flang-aliasanalysis-pointer-component-logic/79252).

In summary, this PR replaces the existing pointer component logic in
Flang's AliasAnalysis implementation. That logic focuses on aliasing
between pointers and non-pointer, non-target composites that have
pointer components. However, it is more conservative than necessary, and
some existing tests expect its current results when less conservative
results seem reasonable.

This PR splits the logic into two cases:

1. Source values are the same: Return MayAlias when one value is the
address of a composite, and the other value is statically the address of
a pointer component of that composite.
2. Source values are different: Return MayAlias when one value is the
address of a composite (actual argument), and the other value is the
address of a pointer (dummy arg) that might dynamically be a component
of that composite.

In both cases, the actual implementation is still more conservative than
described above, but it can be improved further later. Details appear in
the comments.

Additionally, this PR revises the logic that reports MayAlias for a
pointer/target vs. another pointer/target. It constrains the existing
logic to handle only isData cases, and it adds less conservative
handling of !isData cases elsewhere. First, it extends case 2 listed
above to cover the case where the actual argument is the address of a
pointer rather than a composite. Second, it adds a third case: where
target attributes enable aliasing with a dummy argument.



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