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Diffstat (limited to 'contrib/llvm/lib/Target/Blackfin/README.txt')
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diff --git a/contrib/llvm/lib/Target/Blackfin/README.txt b/contrib/llvm/lib/Target/Blackfin/README.txt new file mode 100644 index 0000000..b4c8227 --- /dev/null +++ b/contrib/llvm/lib/Target/Blackfin/README.txt @@ -0,0 +1,244 @@ +//===-- README.txt - Notes for Blackfin Target ------------------*- org -*-===// + +* Condition codes +** DONE Problem with asymmetric SETCC operations +The instruction + + CC = R0 < 2 + +is not symmetric - there is no R0 > 2 instruction. On the other hand, IF CC +JUMP can take both CC and !CC as a condition. We cannot pattern-match (brcond +(not cc), target), the DAG optimizer removes that kind of thing. + +This is handled by creating a pseudo-register NCC that aliases CC. Register +classes JustCC and NotCC are used to control the inversion of CC. + +** DONE CC as an i32 register +The AnyCC register class pretends to hold i32 values. It can only represent the +values 0 and 1, but we can copy to and from the D class. This hack makes it +possible to represent the setcc instruction without having i1 as a legal type. + +In most cases, the CC register is set by a "CC = .." or BITTST instruction, and +then used in a conditional branch or move. The code generator thinks it is +moving 32 bits, but the value stays in CC. In other cases, the result of a +comparison is actually used as am i32 number, and CC will be copied to a D +register. + +* Stack frames +** TODO Use Push/Pop instructions +We should use the push/pop instructions when saving callee-saved +registers. The are smaller, and we may even use push multiple instructions. + +** TODO requiresRegisterScavenging +We need more intelligence in determining when the scavenger is needed. We +should keep track of: +- Spilling D16 registers +- Spilling AnyCC registers + +* Assembler +** TODO Implement PrintGlobalVariable +** TODO Remove LOAD32sym +It's a hack combining two instructions by concatenation. + +* Inline Assembly + +These are the GCC constraints from bfin/constraints.md: + +| Code | Register class | LLVM | +|-------+-------------------------------------------+------| +| a | P | C | +| d | D | C | +| z | Call clobbered P (P0, P1, P2) | X | +| D | EvenD | X | +| W | OddD | X | +| e | Accu | C | +| A | A0 | S | +| B | A1 | S | +| b | I | C | +| v | B | C | +| f | M | C | +| c | Circular I, B, L | X | +| C | JustCC | S | +| t | LoopTop | X | +| u | LoopBottom | X | +| k | LoopCount | X | +| x | GR | C | +| y | RET*, ASTAT, SEQSTAT, USP | X | +| w | ALL | C | +| Z | The FD-PIC GOT pointer (P3) | S | +| Y | The FD-PIC function pointer register (P1) | S | +| q0-q7 | R0-R7 individually | | +| qA | P0 | | +|-------+-------------------------------------------+------| +| Code | Constant | | +|-------+-------------------------------------------+------| +| J | 1<<N, N<32 | | +| Ks3 | imm3 | | +| Ku3 | uimm3 | | +| Ks4 | imm4 | | +| Ku4 | uimm4 | | +| Ks5 | imm5 | | +| Ku5 | uimm5 | | +| Ks7 | imm7 | | +| KN7 | -imm7 | | +| Ksh | imm16 | | +| Kuh | uimm16 | | +| L | ~(1<<N) | | +| M1 | 0xff | | +| M2 | 0xffff | | +| P0-P4 | 0-4 | | +| PA | Macflag, not M | | +| PB | Macflag, only M | | +| Q | Symbol | | + +** TODO Support all register classes +* DAG combiner +** Create test case for each Illegal SETCC case +The DAG combiner may someimes produce illegal i16 SETCC instructions. + +*** TODO SETCC (ctlz x), 5) == const +*** TODO SETCC (and load, const) == const +*** DONE SETCC (zext x) == const +*** TODO SETCC (sext x) == const + +* Instruction selection +** TODO Better imediate constants +Like ARM, build constants as small imm + shift. + +** TODO Implement cycle counter +We have CYCLES and CYCLES2 registers, but the readcyclecounter intrinsic wants +to return i64, and the code generator doesn't know how to legalize that. + +** TODO Instruction alternatives +Some instructions come in different variants for example: + + D = D + D + P = P + P + +Cross combinations are not allowed: + + P = D + D (bad) + +Similarly for the subreg pseudo-instructions: + + D16L = EXTRACT_SUBREG D16, bfin_subreg_lo16 + P16L = EXTRACT_SUBREG P16, bfin_subreg_lo16 + +We want to take advantage of the alternative instructions. This could be done by +changing the DAG after instruction selection. + + +** Multipatterns for load/store +We should try to identify multipatterns for load and store instructions. The +available instruction matrix is a bit irregular. + +Loads: + +| Addr | D | P | D 16z | D 16s | D16 | D 8z | D 8s | +|------------+---+---+-------+-------+-----+------+------| +| P | * | * | * | * | * | * | * | +| P++ | * | * | * | * | | * | * | +| P-- | * | * | * | * | | * | * | +| P+uimm5m2 | | | * | * | | | | +| P+uimm6m4 | * | * | | | | | | +| P+imm16 | | | | | | * | * | +| P+imm17m2 | | | * | * | | | | +| P+imm18m4 | * | * | | | | | | +| P++P | * | | * | * | * | | | +| FP-uimm7m4 | * | * | | | | | | +| I | * | | | | * | | | +| I++ | * | | | | * | | | +| I-- | * | | | | * | | | +| I++M | * | | | | | | | + +Stores: + +| Addr | D | P | D16H | D16L | D 8 | +|------------+---+---+------+------+-----| +| P | * | * | * | * | * | +| P++ | * | * | | * | * | +| P-- | * | * | | * | * | +| P+uimm5m2 | | | | * | | +| P+uimm6m4 | * | * | | | | +| P+imm16 | | | | | * | +| P+imm17m2 | | | | * | | +| P+imm18m4 | * | * | | | | +| P++P | * | | * | * | | +| FP-uimm7m4 | * | * | | | | +| I | * | | * | * | | +| I++ | * | | * | * | | +| I-- | * | | * | * | | +| I++M | * | | | | | + +* Workarounds and features +Blackfin CPUs have bugs. Each model comes in a number of silicon revisions with +different bugs. We learn about the CPU model from the -mcpu switch. + +** Interpretation of -mcpu value +- -mcpu=bf527 refers to the latest known BF527 revision +- -mcpu=bf527-0.2 refers to silicon rev. 0.2 +- -mcpu=bf527-any refers to all known revisions +- -mcpu=bf527-none disables all workarounds + +The -mcpu setting affects the __SILICON_REVISION__ macro and enabled workarounds: + +| -mcpu | __SILICON_REVISION__ | Workarounds | +|------------+----------------------+--------------------| +| bf527 | Def Latest | Specific to latest | +| bf527-1.3 | Def 0x0103 | Specific to 1.3 | +| bf527-any | Def 0xffff | All bf527-x.y | +| bf527-none | Undefined | None | + +These are the known cores and revisions: + +| Core | Silicon | Processors | +|-------------+--------------------+-------------------------| +| Edinburgh | 0.3, 0.4, 0.5, 0.6 | BF531 BF532 BF533 | +| Braemar | 0.2, 0.3 | BF534 BF536 BF537 | +| Stirling | 0.3, 0.4, 0.5 | BF538 BF539 | +| Moab | 0.0, 0.1, 0.2 | BF542 BF544 BF548 BF549 | +| Teton | 0.3, 0.5 | BF561 | +| Kookaburra | 0.0, 0.1, 0.2 | BF523 BF525 BF527 | +| Mockingbird | 0.0, 0.1 | BF522 BF524 BF526 | +| Brodie | 0.0, 0.1 | BF512 BF514 BF516 BF518 | + + +** Compiler implemented workarounds +Most workarounds are implemented in header files and source code using the +__ADSPBF527__ macros. A few workarounds require compiler support. + +| Anomaly | Macro | GCC Switch | +|----------+--------------------------------+------------------| +| Any | __WORKAROUNDS_ENABLED | | +| 05000074 | WA_05000074 | | +| 05000244 | __WORKAROUND_SPECULATIVE_SYNCS | -mcsync-anomaly | +| 05000245 | __WORKAROUND_SPECULATIVE_LOADS | -mspecld-anomaly | +| 05000257 | WA_05000257 | | +| 05000283 | WA_05000283 | | +| 05000312 | WA_LOAD_LCREGS | | +| 05000315 | WA_05000315 | | +| 05000371 | __WORKAROUND_RETS | | +| 05000426 | __WORKAROUND_INDIRECT_CALLS | Not -micplb | + +** GCC feature switches +| Switch | Description | +|---------------------------+----------------------------------------| +| -msim | Use simulator runtime | +| -momit-leaf-frame-pointer | Omit frame pointer for leaf functions | +| -mlow64k | | +| -mcsync-anomaly | | +| -mspecld-anomaly | | +| -mid-shared-library | | +| -mleaf-id-shared-library | | +| -mshared-library-id= | | +| -msep-data | Enable separate data segment | +| -mlong-calls | Use indirect calls | +| -mfast-fp | | +| -mfdpic | | +| -minline-plt | | +| -mstack-check-l1 | Do stack checking in L1 scratch memory | +| -mmulticore | Enable multicore support | +| -mcorea | Build for Core A | +| -mcoreb | Build for Core B | +| -msdram | Build for SDRAM | +| -micplb | Assume ICPLBs are enabled at runtime. | |
