Implements a backend targeting RV32GC and RV64GC, based on Linux standardizing around GC. The assembler is written to make it easy to disable usage of C, but because the sizes of some instruction sequences are compile-time constants, an additional build configuration would need to be defined to make use of it.
The assembler and disassembler cover every RV32/64GC instruction. The simulator covers all instructions except accessing CSRs and the floating point state accessible through such, include accrued exceptions and dynamic rounding mode.
Quirks:
- RISC-V is a compare-and-branch architecture, but some existing "architecture-independent" parts of the Dart compiler assume a condition code architecture. To avoid rewriting these parts, we use a peephole in the assembler to map to compare-and-branch. See Assembler::BranchIf. Luckily nothing depended on taking multiple branches on the same condition code set.
- There are no hardware overflow checks, so we must use Hacker's Delight style software checks. Often these are very cheap: if the sign of one operand is known, a single branch is needed.
- The ranges of RISC-V branches and jumps are such that we use 3 levels of generation for forward branches, instead of the 2 levels of near and far branches used on ARM[64]. Nearly all code is handled by the first two levels with 20-bits of range, with enormous regex matchers triggering the third level that uses aupic+jalr to get 32-bits of range.
- For PC-relative calls in AOT, we always generate auipc+jalr pairs with 32-bits of range, so we never generate trampolines.
- Only a subset of registers are available in some compressed instructions, so we assign the most popular uses to these registers. In particular, THR, TMP[2], CODE and PP. This has the effect of assigning CODE and PP to volatile registers in the C calling convention, whereas they are assigned preserved registers on the other architectures. As on ARM64, PP is untagged; this is so short indices can be accessed with a compressed instruction.
- There are no push or pop instructions, so combining pushes and pops is preferred so we can update SP once.
- The C calling convention has a strongly aligned stack, but unlike on ARM64 we don't need to use an alternate stack pointer. The author ensured language was added to the RISC-V psABI making the OS responsible for realigning the stack pointer for signal handlers, allowing Dart to leave the stack pointer misaligned from the C calling convention's point of view until a foreign call.
- We don't bother with the link register tracking done on ARM[64]. Instead we make use of an alternate link register to avoid inline spilling in the write barrier.
Unimplemented:
- non-trivial FFI cases
- Compressed pointers - No intention to implement.
- Unboxed SIMD - We might make use of the V extension registers when the V extension is ratified.
- BigInt intrinsics
TEST=existing tests for IL level, new tests for assembler/disassembler/simulator
Bug: https://github.com/dart-lang/sdk/issues/38587
Bug: https://github.com/dart-lang/sdk/issues/48164
Change-Id: I991d1df4be5bf55efec5371b767b332d37dfa3e0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/217289
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Opt an initial batch of files under samples, samples-dev,
utils, and runtime/tools/dartfuzz out of null safety in preparation
for switching the flag on by default.
Change-Id: Icdfd52a5a969e678a7205903332f73fe3841c223
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/166960
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Leaf Petersen <leafp@google.com>
This reverts commit 9464eb51f5.
Reason for revert: Causes a failure in the Analyzer bot, some analysis errors.
Original change's description:
> [ DartFuzz ] Prevent generated programs from explicitly throwing OutOfMemoryError
>
> Programs generated by dartfuzz.dart explicitly look for OOM errors and
> return with a specific error code (254) to notify dartfuzz_test.dart
> that the program exited after running out of memory. If both
> configurations being tested return 254, the result for that fuzzing run
> is counted as "skipped", artificially inflating the "skipped" count.
>
> Fixes https://github.com/dart-lang/sdk/issues/40493
>
> Change-Id: I552dbd497fe514da929b08a7a523616d1d3db538
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/134903
> Auto-Submit: Ben Konyi <bkonyi@google.com>
> Reviewed-by: Ryan Macnak <rmacnak@google.com>
TBR=bkonyi@google.com,rmacnak@google.com,asiva@google.com
Change-Id: I23e286bb9c5aba1513fbc66bcb6d49221cbd4aba
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/135000
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Siva Annamalai <asiva@google.com>
Programs generated by dartfuzz.dart explicitly look for OOM errors and
return with a specific error code (254) to notify dartfuzz_test.dart
that the program exited after running out of memory. If both
configurations being tested return 254, the result for that fuzzing run
is counted as "skipped", artificially inflating the "skipped" count.
Fixes https://github.com/dart-lang/sdk/issues/40493
Change-Id: I552dbd497fe514da929b08a7a523616d1d3db538
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/134903
Auto-Submit: Ben Konyi <bkonyi@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Comparing floating point results from different architectures can lead
to false divergences due to floating point errors or slightly different
implementations of specific operations (e.g., Float32x4.clamp behaves
differently around 0.0 for ARM and x64).
Should fix false divergences related to https://github.com/dart-lang/sdk/issues/40426
Change-Id: Ife0ab07d20e87add4e754e328bb8f7389920021d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/134573
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>
- Updated reproduction commands to not include bot paths (should be
copy-pasteable and runnable from $SDK_ROOT now).
- Fixed issue where Dart SDK revision wasn't being printed on the bots
Change-Id: Ia53986332eb7997d5b3911c5de4e5ce1d61e6eb3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/134420
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>
Konstantin Shcheglov