[Patch][V5][Patch 2/2]Enable -Wuninitialized + -ftrivial-auto-var-init for address taken variables.

[Qing Zhao via Gcc-patches]

Hi, Richard,

This is the updated version for the change of "Enable -Wuninitialized + 
-ftrivial-auto-var-init for  address taken variables”.

Compared to the previous patch, I mainly made the following change:

Delete the 4th parameter of “warn_uninit”, construct the warning message string 
based on the value of OPT and VAR.

This patch has been bootstrapped and regressing tested on both X86 and aarch64.

Okay for GCC12?

thanks.

Qing.

==================================
Enable -Wuninitialized + -ftrivial-auto-var-init for address
 taken variables.

With -ftrivial-auto-var-init, the address taken auto variable is replaced with
a temporary variable during gimplification, and the original auto variable might
be eliminated by compiler optimization completely. As a result, the current
uninitialized warning analysis cannot get enough information from the IR,
therefore the uninitialized warnings for address taken variable cannot be
issued based on the current implemenation of -ftrival-auto-var-init.

For more info please refer to:
https://gcc.gnu.org/pipermail/gcc-patches/2021-August/577431.html

In order to improve this situation, we can improve uninitialized analysis
for address taken auto variables with -ftrivial-auto-var-init as following:

for the following stmt:

    _1 = .DEFERRED_INIT (4, 2, &"alt_reloc"[0]);
    if (_1 != 0)

The original variable DECL has been eliminated from the IR, all the necessary
information that is needed for reporting the warnings for DECL can be acquired
from the call to .DEFERRED_INIT.

    A. the name string of DECL from the 3rd parameter of the call;
    B. the location of the DECL from the location of the call;
    C. the call can also be used to hold the information on whether the warning
       has been issued or not to suppress warning messages when needed;

The current testing cases for uninitialized warnings + -ftrivial-auto-var-init
are adjusted to reflect the fact that we can issue warnings for address taken
variables.

gcc/ChangeLog:

2022-01-14  qing zhao  <qing.z...@oracle.com>

        * tree-ssa-uninit.c (warn_uninit): Delete the 4th parameter. Handle
        .DEFERRED_INIT call with an anonymous SSA_NAME specially.
        (check_defs): Handle .DEFERRED_INIT call with an anonymous SSA_NAME
        specially.
        (warn_uninit_phi_uses): Delete the 4th actual when call warn_uninit.
        (warn_uninitialized_vars): Likewise.
        (warn_uninitialized_phi): Likewise.

The complete patch is:

0001-Enable-Wuninitialized-ftrivial-auto-var-init-for-add.patch
Description: 0001-Enable-Wuninitialized-ftrivial-auto-var-init-for-add.patch