x86: Improve -malign-branch
According to intel SDM manual, not all compare flag-modifying instructions
are marcro-fusible with subsequent jcc instructions. For those non-fusible
instructions, -malign-branch doesn't need to align them, only jcc itself
needs 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 instruction.
Restriction 2:
/* Table 3-2. Macro-Fusible Instructions in Haswell Microarchitecture
Note it also works for Skylake and Cascadelake.
---------------------------------------------------------------------
| 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 |
Update maybe_fused_with_jcc_p to check if operands of CMP like instructions
can be fused with condition jump.
* 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.
7 files changed
