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.
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;
