Warning: It blocks containing 32-bit Thumb instructions are deprecated in ARMv8 with GCC 4.9

Dear colleagues.

I am compiling the Intel TBB in an effort to optimize my code to the Cortex-M53, however, because I was still forced to use GCC 4.9 I'm getting some warning messages about the use of  32bit Thumb Instrucions in IT blocks:

Warning: It blocks containing 32-bit Thumb instructions are deprecated in ARMv8

I know it's a bug in this release and that may already be solved in GCC version 5.3 but still can not migrate this environment for a new version.

This can bring some instability to my code or can be ignored by time?

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  • Hi Carlos Delfino,

    This can bring some instability to my code or can be ignored by time?

    You can ignore it.
    I checked the Cortex-A53 TRM.
    The warning should be produced only in the case that SCTLR_EL1.ITD is '1'.
    As the reset value of SCTLR_EL1.ITD is '0', the IT instruction functionality is enabled and there would be no restrictions.
    Therefore, it would be shown as a warning.
    Also I checked GCC 5.4, and found  the same messages as GCC 4.9 were generated, but the word 'Warning' was omitted.
    As the results, you had not betther be worried about it.

    Best regards,

    Yasuhiko Koumoto.

Reply
  • Hi Carlos Delfino,

    This can bring some instability to my code or can be ignored by time?

    You can ignore it.
    I checked the Cortex-A53 TRM.
    The warning should be produced only in the case that SCTLR_EL1.ITD is '1'.
    As the reset value of SCTLR_EL1.ITD is '0', the IT instruction functionality is enabled and there would be no restrictions.
    Therefore, it would be shown as a warning.
    Also I checked GCC 5.4, and found  the same messages as GCC 4.9 were generated, but the word 'Warning' was omitted.
    As the results, you had not betther be worried about it.

    Best regards,

    Yasuhiko Koumoto.

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