Hi,
I read the following on IT block in ARM Thumb2 instruction. I don't understand
the last sentence on AL to get the changed behavior.
Could you explain it to me?
Thanks,
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A8.6.50 IT
If Then makes up to four following instructions (the IT block) conditional.
The conditions for the instructions in the IT block can be the same, or some
of them can be the inverse of others.
IT does not affect the condition code flags. Branches to any instruction in
the IT block are not permitted, apart from those performed by exception
returns.
16-bit instructions in the IT block, other than CMP, CMN and TST, do not set
the condition code flags. The AL condition can be specified to get this
changed behavior without conditional execution.
Hello,
in the IT block, the condition codes are not changed with exceptions of CMP, CMN and TST. You can inhibit the condition code change of instructions (such as ADDS) in the IT block. To specify AL condition to the IT instruction, it means all instructions would be always executed but the condition codes would not be changed.
Best regards,
Yasuhiko Koumoto.
See the section 'interesting optimization possibilities' in
Condition Codes 3: Conditional Execution in Thumb-2