diff options
| author | Richard Henderson <richard.henderson@linaro.org> | 2021-06-12 21:32:27 -0700 |
|---|---|---|
| committer | Richard Henderson <richard.henderson@linaro.org> | 2021-06-29 10:04:57 -0700 |
| commit | 587195bd5905deefe90242bbd210b9bba76ca093 (patch) | |
| tree | ca7d75039083a054dd3cb1ad99a61a96499131ff /tcg/README | |
| parent | 4f862f79ca497f68d147520e847f86d69eec950b (diff) | |
tcg: Add flags argument to bswap opcodes
This will eventually simplify front-end usage, and will allow
backends to unset TCG_TARGET_HAS_MEMORY_BSWAP without loss of
optimization.
The argument is added during expansion, not currently exposed to the
front end translators. The backends currently only support a flags
value of either TCG_BSWAP_IZ, or (TCG_BSWAP_IZ | TCG_BSWAP_OZ),
since they all require zero top bytes and leave them that way.
At the existing call sites we pass in (TCG_BSWAP_IZ | TCG_BSWAP_OZ),
except for the flags-ignored cases of a 32-bit swap of a 32-bit
value and or a 64-bit swap of a 64-bit value, where we pass 0.
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Diffstat (limited to 'tcg/README')
| -rw-r--r-- | tcg/README | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/tcg/README b/tcg/README index 8510d823e3..c2e7762a37 100644 --- a/tcg/README +++ b/tcg/README @@ -295,19 +295,25 @@ ext32u_i64 t0, t1 8, 16 or 32 bit sign/zero extension (both operands must have the same type) -* bswap16_i32/i64 t0, t1 +* bswap16_i32/i64 t0, t1, flags -16 bit byte swap on a 32/64 bit value. It assumes that the two/six high order -bytes are set to zero. +16 bit byte swap on the low bits of a 32/64 bit input. +If flags & TCG_BSWAP_IZ, then t1 is known to be zero-extended from bit 15. +If flags & TCG_BSWAP_OZ, then t0 will be zero-extended from bit 15. +If flags & TCG_BSWAP_OS, then t0 will be sign-extended from bit 15. +If neither TCG_BSWAP_OZ nor TCG_BSWAP_OS are set, then the bits of +t0 above bit 15 may contain any value. -* bswap32_i32/i64 t0, t1 +* bswap32_i64 t0, t1, flags -32 bit byte swap on a 32/64 bit value. With a 64 bit value, it assumes that -the four high order bytes are set to zero. +32 bit byte swap on a 64-bit value. The flags are the same as for bswap16, +except they apply from bit 31 instead of bit 15. -* bswap64_i64 t0, t1 +* bswap32_i32 t0, t1, flags +* bswap64_i64 t0, t1, flags -64 bit byte swap +32/64 bit byte swap. The flags are ignored, but still present +for consistency with the other bswap opcodes. * discard_i32/i64 t0 |