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[ARM] Do not emit ldrexd/strexd on Cortex-M chips

Authored by aykevl on Feb 2 2021, 11:58 AM.

Description

[ARM] Do not emit ldrexd/strexd on Cortex-M chips

The ldrexd/strexd instructions are not supported on M-class chips, see
for example
https://developer.arm.com/documentation/dui0489/e/arm-and-thumb-instructions/memory-access-instructions/ldrex-and-strex
which says:

All these 32-bit Thumb instructions are available in ARMv6T2 and
above, except that LDREXD and STREXD are not available in the ARMv7-M
architecture.

Looking at the ARMv8-M architecture, it appears that these instructions
aren't supported either. The Architecture Reference Manual lists
ldrex/strex but not ldrexd/strexd:
https://developer.arm.com/documentation/ddi0553/bn/

Godbolt example on LLVM 11.0.0, which incorrectly emits ldrexd/strexd
instructions: https://llvm.godbolt.org/z/5qqPnE

Differential Revision: https://reviews.llvm.org/D95891

Details

Committed
aykevlFeb 4 2021, 12:55 PM
Differential Revision
D95891: [ARM] Do not emit ldrexd/strexd on Cortex-M chips
Parents
rGcd2f65b71a42: Correct some confused diagnostic terminology
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