[PATCH] Separate macro-fusible instructions from not for -mbranches-within-32B-boundaries

[Hongtao Liu]

On Fri, Feb 28, 2020 at 4:55 PM Hongtao Liu <crazylht@gmail.com> wrote:
>
> Hi:
>     This is subsequent patch for JCC Code Erratum.
>     Refer to http://sourceware-org.1504.n7.nabble.com/PATCH-0-5-i386-Optimize-for-Jump-Conditional-Code-Erratum-tt598005.html#none
>
>     According to intel SDM manual, not all compare flag-modifying
> instructions are marcro-fusible with subsequent jcc instruction. For
> those not, -mbranches-within-32B-boundaries need't align them as
> FUSED_JCC_PADDING, only jcc itself need to be aligned. Here are 2
> restrictions which separate macro-fusible instruction from not
>
>     Restriction 1:
>     If TEST/AND/CMP/ADD/SUB/INC/DEC is one of the following format:
>
>        cmp m, imm
>        add m, imm
>        sub m, imm
>        test m, imm
>        and m, imm
>        inc m
>        dec m
>
>     it is unfusible with any jcc instructions.
>
>     Restriction 2:
>     /* Table 3-2. Macro-Fusible Instructions in Haswell Microarchitecture
>     ---------------------------------------------------------------------
>     |   JCC   | ADD/SUB/CMP | INC/DEC | TEST/AND |
>     | ------  | ----------- | ------- | -------- |
>     |   Jo    |      N      |    N    |     Y    |
>     |   Jno   |      N      |    N    |     Y    |
>     |  Jc/Jb  |      Y      |    N    |     Y    |
>     | Jae/Jnb |      Y      |    N    |     Y    |
>     |  Je/Jz  |      Y      |    Y    |     Y    |
>     | Jne/Jnz |      Y      |    Y    |     Y    |
>     | Jna/Jbe |      Y      |    N    |     Y    |
>     | Ja/Jnbe |      Y      |    N    |     Y    |
>     |   Js    |      N      |    N    |     Y    |
>     |   Jns   |      N      |    N    |     Y    |
>     |  Jp/Jpe |      N      |    N    |     Y    |
>     | Jnp/Jpo |      N      |    N    |     Y    |
>     | Jl/Jnge |      Y      |    Y    |     Y    |
>     | Jge/Jnl |      Y      |    Y    |     Y    |
>     | Jle/Jng |      Y      |    Y    |     Y    |
>     | Jg/Jnle |      Y      |    Y    |     Y    |
>
>
> Changelog
>
>             * gas/config/tc-i386.h (i386_tc_frag_data): Add member mf_type.
>             (TC_FRAG_INIT): Init mf_type.
>             * gas/config/tc-i386.c (enum mf_jcc_kind): New enum.
>             (enum mf_cmp_kind): Ditto.
>             (maybe_fused_with_jcc_p): Add argument mf_cmp_p to get
>             mf_type of corresponding instructons, exclude unfusible
>             instructions.
>             (add_fused_jcc_padding_frag_p): Likewise.
>             (add_branch_padding_frag_p): Likewise.
>             (output_insn): Record mf_type for corresponding instructions.
>             (i386_macro_fusible_p): New function.
>             (i386_next_fusible_jcc_frag): Rename from i386_next_jcc_frag,
>             add argument cmp_fragP to return next fusible jcc frag only.
>             (i386_classify_machine_dependant_frag): Seperate macro-fusible
>             instructions from condition jump.
>             * gas/testsuite/gas/i386/align-branch-9.s: New file.
>             * gas/testsuite/gas/i386/align-branch-9.d: Ditto.
>             * gas/testsuite/gas/i386/x86-64-align-branch-9.s: Ditto.
>             * gas/testsuite/gas/i386/x86-64-align-branch-9.d: Ditto.
>             * gas/testsuite/gas/i386/i386.exp: Run new tests.
>
> --
> BR,
> Hongtao

Add patch.

-- 
BR,
Hongtao
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