Armv7-M: Default to .w for better alignment #157
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dop-amin
reviewed
Jan 13, 2025
| # SLOTHY is not sufficient. | ||
| # As currently, we don't have a model of the instruction encodings, | ||
| # there is no principled way to reason about it. | ||
| if thumb: |
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Probably Arch specific code should not go here. But also don't have a good quick fix in mind right now.
Currently, we maintain the instruction-width modifiers as they are in the input code (except for some exceptions). However, this can negatively impact performance as SLOTHY may break code-alignment. This commit changes the Armv7-M instruction writer, to output .w for all instructions resulting in the best performance (modulo the size of the instruction cache). Unfortunately, LLVM (in the selftest) stumbles over some of these .w modifiers in places where they do not have any effect. To work around that, we remove the modifiers for the selftest.
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Currently, we maintain the instruction-width modifiers as they are in the input code (except for some exceptions). However, this can negatively impact performance as SLOTHY may break code-alignment.
This commit changes the Armv7-M instruction writer, to output .w for all instructions resulting in the best performance (modulo the size of the instruction cache).
Unfortunately, LLVM (in the selftest) stumbles over some of these .w modifiers in places where they do not have any effect. To work around that, we remove the modifiers for the selftest.