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tcg: Use "unspecified behavior" for shifts 

Change the definition such that shifts are not allowed to crash
for any input.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
master
Richard Henderson 2014-03-18 08:21:44 -07:00
parent ad5171dbd4
commit 20022fa15f
1 changed files with 13 additions and 5 deletions
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18
tcg/README
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@ -36,6 +36,12 @@ or a memory location which is stored in a register outside QEMU TBs
A TCG "basic block" corresponds to a list of instructions terminated
by a branch instruction.
An operation with "undefined behavior" may result in a crash.
An operation with "unspecified behavior" shall not crash. However,
the result may be one of several possibilities so may be considered
an "undefined result".
3) Intermediate representation
3.1) Introduction
@ -239,23 +245,25 @@ t0=t1|~t2
* shl_i32/i64 t0, t1, t2
t0=t1 << t2. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
t0=t1 << t2. Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
* shr_i32/i64 t0, t1, t2
t0=t1 >> t2 (unsigned). Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
t0=t1 >> t2 (unsigned). Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
* sar_i32/i64 t0, t1, t2
t0=t1 >> t2 (signed). Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
t0=t1 >> t2 (signed). Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
* rotl_i32/i64 t0, t1, t2
Rotation of t2 bits to the left. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
Rotation of t2 bits to the left.
Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
* rotr_i32/i64 t0, t1, t2
Rotation of t2 bits to the right. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
Rotation of t2 bits to the right.
Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
********* Misc