[clang] [clang][driver] Allow unaligned access on ARMv7 and higher by default (PR #82400)

[Paul Kirth via cfe-commits]

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@@ -305,6 +305,16 @@ X86 Support
 Arm and AArch64 Support
 ^^^^^^^^^^^^^^^^^^^^^^^
 
+- ARMv6+ targets now default to allowing unaligned access, except Armv6-M, and
+  Armv8-M without the Main Extension. Baremetal targets should check that the
+  new default will work with their system configurations, since it requires
+  that SCTLR.A is 0, SCTLR.U is 1, and that the memory in question is
+  configured as "normal" memory. We've made the value judgment that the
+  performance gains here outweigh breakages, since it is difficult to identify
+  performance loss from disabling unaligned access, but incorrect enabling
+  unaligned access will generate an obvious alignment fault on ARMv7+. This is
+  also the default setting for ARM's downstream compilers.
+
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ilovepi wrote:

@efriedma-quic @davemgreen Is this more in line with what you would expect in the release notes?

https://github.com/llvm/llvm-project/pull/82400