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tcg: Use "unspecified behavior" for shifts

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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>
This commit is contained in:
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 A TCG "basic block" corresponds to a list of instructions terminated
by a branch instruction. 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) Intermediate representation
3.1) Introduction 3.1) Introduction
@ -239,23 +245,25 @@ t0=t1|~t2
* shl_i32/i64 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 * 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 * 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 * 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 * 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 ********* Misc