Store merging refuses to widen a group below its alignment on a STRICT_ALIGNMENT
target, even where the target has a single-instruction misaligned move. This
adds a hook for "is the misaligned access cheap", uses it in the pass, and
implements it for arm.
It is split because the three parts want different reviewers: the hook is a
global-maintainer question, the pass change is store merging, and the last patch
is arm. Patches 1/3 and 2/3 change no generated code on any target, because the
hook defaults to false wherever STRICT_ALIGNMENT is true; nothing moves until
3/3.
Bootstrapped and regression tested on x86_64-pc-linux-gnu, and built after 1/3
alone and 1/3+2/3
and with the whole series (STRICT_ALIGNMENT is 0 there, so the hook is false and
the new path is not exercised); regression tested on arm-none-eabi with arm.exp,
dg.exp and tree-ssa.exp, on the default, cortex-a15 and cortex-m0 boards.
Dominic P (3):
target: add TARGET_MISALIGNED_ACCESS_CHEAP_P
tree-optimization: merge stores below their alignment where the target
says it is cheap
arm: allow merged stores below their alignment
gcc/config/arm/arm.cc | 13 ++++++
gcc/doc/tm.texi | 19 ++++++++
gcc/doc/tm.texi.in | 2 +
gcc/gimple-ssa-store-merging.cc | 26 +++++++++--
gcc/target.def | 21 +++++++++
gcc/targhooks.cc | 9 ++++
gcc/targhooks.h | 1 +
.../gcc.dg/torture/store-merging-misaligned.c | 43 +++++++++++++++++++
.../gcc.target/arm/store-merge-unaligned-2.c | 18 ++++++++
.../gcc.target/arm/store-merge-unaligned-3.c | 16 +++++++
.../gcc.target/arm/store-merge-unaligned-4.c | 15 +++++++
.../gcc.target/arm/store-merge-unaligned-5.c | 25 +++++++++++
.../gcc.target/arm/store-merge-unaligned-6.c | 18 ++++++++
.../gcc.target/arm/store-merge-unaligned.c | 27 ++++++++++++
14 files changed, 250 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/torture/store-merging-misaligned.c
create mode 100644 gcc/testsuite/gcc.target/arm/store-merge-unaligned-2.c
create mode 100644 gcc/testsuite/gcc.target/arm/store-merge-unaligned-3.c
create mode 100644 gcc/testsuite/gcc.target/arm/store-merge-unaligned-4.c
create mode 100644 gcc/testsuite/gcc.target/arm/store-merge-unaligned-5.c
create mode 100644 gcc/testsuite/gcc.target/arm/store-merge-unaligned-6.c
create mode 100644 gcc/testsuite/gcc.target/arm/store-merge-unaligned.c
--
2.55.0
