On December 12, 2021 1:22:09 PM GMT+01:00, Jan Hubicka via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>Hi,
>ipa-modref is using TBAA to disambiguate memory accesses inter-procedurally.
>This sometimes breaks programs with TBAA violations including clang with LTO.
>To workaround that one can use -fno-strict-aliasing or -fno-ipa-modref which
>are both quite big hammers. So I added -fipa-strict-aliasing patch that
>controls only the TBAA based analysis in ipa-modref while keeping all other
>optimizations.
>
>Bootstrapped/regtested x86_64-linux, will commit it shortly.
I think at the documentation level we need to clarify that TBAA exposed by
inlining is not considered IPA. The current wording is confusing in this
regard. Or we need to somehow preserve a TBAA barrier at inline instances (like
drop all inlined refs to alias set zero)
>gcc/ChangeLog:
>
>2021-12-12 Jan Hubicka <hubi...@ucw.cz>
>
> * common.opt: Add -fipa-strict-aliasing.
> * doc/invoke.texi: Document -fipa-strict-aliasing.
> * ipa-modref.c (modref_access_analysis::record_access): Honor
> -fipa-strict-aliasing.
> (modref_access_analysis::record_access_lto): Likewise.
>
>diff --git a/gcc/common.opt b/gcc/common.opt
>index 445a53a265c..673813f34ab 100644
>--- a/gcc/common.opt
>+++ b/gcc/common.opt
>@@ -1945,6 +1945,10 @@ fira-algorithm=
> Common Joined RejectNegative Enum(ira_algorithm) Var(flag_ira_algorithm)
> Init(IRA_ALGORITHM_CB) Optimization
> -fira-algorithm=[CB|priority] Set the used IRA algorithm.
>
>+fipa-strict-aliasing
>+Common Var(flag_ipa_strict_aliasing) Init(1) Optimization
>+Assume strict aliasing rules apply across function boundaries.
>+
> Enum
> Name(ira_algorithm) Type(enum ira_algorithm) UnknownError(unknown IRA
> algorithm %qs)
>
>diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
>index 9b4371b9213..afd85afe476 100644
>--- a/gcc/doc/invoke.texi
>+++ b/gcc/doc/invoke.texi
>@@ -570,7 +570,7 @@ Objective-C and Objective-C++ Dialects}.
> -fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops@gol
> -fsplit-paths @gol
> -fsplit-wide-types -fsplit-wide-types-early -fssa-backprop -fssa-phiopt
> @gol
>--fstdarg-opt -fstore-merging -fstrict-aliasing @gol
>+-fstdarg-opt -fstore-merging -fstrict-aliasing -fipa-strict-aliasing @gol
> -fthread-jumps -ftracer -ftree-bit-ccp @gol
> -ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol
> -ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts @gol
>@@ -12423,6 +12423,15 @@ int f() @{
> The @option{-fstrict-aliasing} option is enabled at levels
> @option{-O2}, @option{-O3}, @option{-Os}.
>
>+@item -fipa-strict-aliasing
>+@opindex fipa-strict-aliasing
>+Constrols whether rules of @option{-fstrict-aliasing} can be applied across
>+function boundaries. This option is effective only in combination with
>+@option{-fstrict-aliasing} and does not prevent optimization across function
>+boundry in case function has been inlined.
>+
>+The @option{-fipa-strict-aliasing} option is enabled by default.
>+
> @item -falign-functions
> @itemx -falign-functions=@var{n}
> @itemx -falign-functions=@var{n}:@var{m}
>diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
>index 2c89c63baf6..d6bd9d33278 100644
>--- a/gcc/ipa-modref.c
>+++ b/gcc/ipa-modref.c
>@@ -999,9 +999,11 @@ modref_access_analysis::record_access (modref_records *tt,
> ao_ref *ref,
> modref_access_node &a)
> {
>- alias_set_type base_set = !flag_strict_aliasing ? 0
>+ alias_set_type base_set = !flag_strict_aliasing
>+ || !flag_ipa_strict_aliasing ? 0
> : ao_ref_base_alias_set (ref);
>- alias_set_type ref_set = !flag_strict_aliasing ? 0
>+ alias_set_type ref_set = !flag_strict_aliasing
>+ || !flag_ipa_strict_aliasing ? 0
> : (ao_ref_alias_set (ref));
> if (dump_file)
> {
>@@ -1021,7 +1023,7 @@ modref_access_analysis::record_access_lto
>(modref_records_lto *tt, ao_ref *ref,
> /* get_alias_set sometimes use different type to compute the alias set
> than TREE_TYPE (base). Do same adjustments. */
> tree base_type = NULL_TREE, ref_type = NULL_TREE;
>- if (flag_strict_aliasing)
>+ if (flag_strict_aliasing && flag_ipa_strict_aliasing)
> {
> tree base;
>
