ARM's Clang and GCC embedded compilers default to allowing unaligned
access for ARMv7+. This patch changes the Clang driver default to match.
Users can opt out with `-mno-unaligned-access`.
Fixes#59560
Similar to d39b4ce3ce8a3c256e01bdec2b140777a332a633
Using "eabi" or "gnueabi" for aarch64 targets is a common mistake and
warned by Clang Driver. We want to avoid them elsewhere as well. Just
use the common "aarch64" without other triple components.
Windows on armv7 is as alignment tolerant as Linux.
The alignment considerations in the Windows on ARM ABI are documented
at https://docs.microsoft.com/en-us/cpp/build/overview-of-arm-abi-conventions?view=msvc-160#alignment.
The document doesn't explicitly say in which state the OS configures
the SCTLR.A register (and it's not accessible from user space to
inspect), but in practice, unaligned loads/stores do work and seem
to be as fast as aligned loads and stores. (Unaligned strd also does
seem to work, contrary to Linux, but significantly slower, as they're
handled by the kernel - exactly as the document describes.)
Differential Revision: https://reviews.llvm.org/D109960
This commit changes the driver to save subtarget feature "+strict-align"
to the IR instead of using backend option "aarch64-strict-align". This is
needed for LTO.
rdar://problem/21529937
llvm-svn: 243518
This commit changes the driver to save subtarget feature "+strict-align" to the
IR instead of using backend option "arm-strict-align". This is needed for LTO.
Also, move the logic in ARM backend that was deciding whether strict alignment
should be forced to the front-end.
rdar://problem/21529937
http://reviews.llvm.org/D11472
llvm-svn: 243489
The -mstrict-align option was originally added in r167619 as a target-
independent option. It was then changed in r167623 to be implemented with an
ARM-specific backend option, even though the code remained in the
target-independent Clang::ConstructJob function. This means that if you used
the -mstrict-align option with a non-ARM target, you would still get the
-arm-strict-align option getting passed to the backend, which was harmless
but gross. The driver option was then replaced by the GCC-compatible
-m[no-]unaligned-access option (r189175) and modified to work with AArch64
(r208075). However, in the process, the help text for -mstrict-align was
incorrectly changed to show it as only being supported for AArch64. Even worse,
the logic for handling these options together with -mkernel was wrong for
AArch64, where -mkernel does not currently imply strict alignment.
This patch fixes up all of those things. Besides the obvious change to the
option help text, it moves the logic into the ARM and AArch64-specific parts
of the driver, so that the option will be correctly ignored for non-ARM
targets. <rdar://problem/17823697>
llvm-svn: 214148
Passing inconsistent munaligned-access / mno-unaligned-access
flags, intentionally resulted in a warning and the flag
no-unaligned-access being used.
Gcc does, at least in practice, use the last flag in such a
case. This patch updates clang behaviour accordingly; use the
last flag or base alignment behaviour on the target (which
llvm will do if no flag is explicitly passed)
Patch by Jeroen Hofstee.
llvm-svn: 189542
