tree 1cfe668a14e35d6787222a7d6ab4ff159af70597
parent bb7b70ab85fb9d185d1fa6bad192c90fe9c17ff3
author Hongtao Liu <hongtao.liu@intel.com> 1583245297 -0800
committer H.J. Lu <hjl.tools@gmail.com> 1583245297 -0800

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.