[PATCH] D65615: [BPF] annotate DIType metadata for builtin preseve_array_access_index()

[Yonghong Song via Phabricator via cfe-commits]

yonghong-song created this revision.
yonghong-song added a reviewer: ast.
Herald added subscribers: kristina, arphaman, aprantl.
Herald added a project: clang.

Previously, debuginfo types are annotated to
IR builtin preserve_struct_access_index() and
preserve_union_access_index(), but not
preserve_array_access_index(). The debug info
is useful to identify the root type name which
later will be used for type comparison.

For user access without explicit type conversions,
the previous scheme works as we can ignore intermediate
compiler generated type conversions (e.g., from union types to
union members) and still generate correct access index string.

The issue comes with user explicit type conversions, e.g.,
converting an array to a structure like below:

  struct t { int a; char b[40]; };
  struct p { int c; int d; };
  struct t *var = ...;
  ... __builtin_preserve_access_index(&(((struct p *)&(var->b[0]))->d)) ...

Although BPF backend can derive the type of &(var->b[0]),
explicit type annotation make checking more consistent
and less error prone.

Another benefit is for multiple dimension array handling.
For example,

  struct p { int c; int d; } g[8][9][10];
  ... __builtin_preserve_access_index(&g[2][3][4].d) ...

It would be possible to calculate the number of "struct p"'s
before accessing its member "d" if array debug info is
available as it contains each dimension range.

This patch enables to annotate IR builtin preserve_array_access_index()
with either debuginfo array type or pointer type,
depending on user expression.


Repository:
  rC Clang

https://reviews.llvm.org/D65615

Files:
  lib/CodeGen/CGExpr.cpp
  test/CodeGen/builtin-preserve-access-index-array.c
  test/CodeGen/builtin-preserve-access-index.c

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