Drop immediates array #618
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chfast
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Codecov Report
@@ Coverage Diff @@
## master #618 +/- ##
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- Coverage 98.37% 98.36% -0.01%
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Files 69 69
Lines 9654 9622 -32
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- Hits 9497 9465 -32
Misses 157 157 |
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| push(code.immediates, local_idx); | ||
| break; | ||
| code.instructions.push_back(opcode); |
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Why use push_back for these and not push(code.instructions, opcode)?
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This is the copy of line after the switch.
But I can reverse the question: Why use push(code.instructions, opcode) for these when code.instructions.push_back(opcode) is enough.
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Maybe push should be renamed to push_immediate, and optionally a new helper push_opcode added
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Maybe push should be renamed to push_immediate, and optionally a new helper push_opcode added
That would be nice for readability, in a separate PR.
axic
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Oct 22, 2020
| break; | ||
| code.instructions.push_back(opcode); | ||
| push(code.instructions, uint32_t{0}); // Diff to the else instruction | ||
| continue; |
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Why are many of these changed to continue?
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The continue skips the code.instructions.push_back(opcode); after the switch because you do it here before pushing the immediates.
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As opcode is always the first to be pushed, would it be better to move code.instructions.push_back(opcode); to before the switch?
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Possible currently, but I'm not sure this will stand long term. In #622 I present a way to skip noop instructions in parsing. Also we can replace return with br, etc. So I think the control what opcode is pushed if any on the instruction granularity is useful.
Alternatively, we can push the opcode, and the "pop" it or replace it in some cases.
axic
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Oct 22, 2020
axic
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chfast
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Oct 23, 2020
| break; | ||
| code.instructions.push_back(opcode); | ||
| push(code.instructions, uint32_t{0}); // Diff to the else instruction | ||
| continue; |
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The continue skips the code.instructions.push_back(opcode); after the switch because you do it here before pushing the immediates.
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| push(code.immediates, local_idx); | ||
| break; | ||
| code.instructions.push_back(opcode); |
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This is the copy of line after the switch.
But I can reverse the question: Why use push(code.instructions, opcode) for these when code.instructions.push_back(opcode) is enough.
test/unittests/parser_expr_test.cpp
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| ElementsAre(Instr::i32_const, 0, 0, 0, 0, Instr::loop, Instr::br, /*arity:*/ 0, 0, 0, 0, | ||
| /*code_offset:*/ 5, 0, 0, 0, /*stack_drop:*/ 0, 0, 0, 0, Instr::end, Instr::drop, | ||
| Instr::end)); | ||
| // EXPECT_EQ(module_parent_stack->codesec[0].immediates, |
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gumb0
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Oct 23, 2020
lib/fizzy/parser_expr.cpp
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| // br immediates from `then` branch will need to be filled at the end of `else` | ||
| control_stack.top().br_immediate_offsets = std::move(frame_br_immediate_offsets); | ||
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| // Placeholders for immediate values, filled at the matching end instructions. |
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Move this comment one line down, to before pushing the immediate
Suggested change
| // Placeholders for immediate values, filled at the matching end instructions. | |
| // Placeholder for immediate value, filled at the matching end instructions. |
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| push(code.immediates, local_idx); | ||
| break; | ||
| code.instructions.push_back(opcode); |
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Maybe push should be renamed to push_immediate, and optionally a new helper push_opcode added
lib/fizzy/parser_expr.cpp
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| code.instructions.push_back(opcode); | ||
| push(code.instructions, uint32_t{0}); // Diff to the end instruction. | ||
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| // Fill in if's immediates with offsets of first instruction in else block. |
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Suggested change
| // Fill in if's immediates with offsets of first instruction in else block. | |
| // Fill in if's immediate with offset of first instruction in else block. |
lib/fizzy/parser_expr.cpp
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| if (frame.instruction == Instr::if_ || frame.instruction == Instr::else_) | ||
| { | ||
| // We're at the end instruction of the if block without else or at the end of | ||
| // else block. Fill in if/else's immediates with offsets of first instruction |
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Suggested change
| // else block. Fill in if/else's immediates with offsets of first instruction | |
| // else block. Fill in if/else's immediate with offset of first instruction |
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My classic benchmarks, GCC10 LTO on Haswell 4GHz. The parsing got slower. There can be two reasons for that: we allocate differently - single array, and the parser loop is more complex. |
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chfast
commented
Oct 23, 2020
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| // The instructions bytecode without immediate values. | ||
| // https://webassembly.github.io/spec/core/binary/instructions.html | ||
| std::vector<uint8_t> instructions; |
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I also tried using bytes, but the performance is the same. So I'm happy to leave vector as it is simpler internally (string has SSO which is useless in this case).
gumb0
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Oct 23, 2020
| const auto module = parse(bin); | ||
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| for (const auto param : {0u, 1u}) | ||
| for (const auto param : {0u}) |
gumb0
reviewed
Oct 23, 2020
| "00000000"_bytes; // stack_drop | ||
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| EXPECT_EQ(code.immediates.substr(br_table_imm_offset, expected_br_imm.size()), expected_br_imm); | ||
| Instr::local_get, 0, 0, 0, 0, Instr::br_table, |
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These tests are super annoying, I'm not checking all the offsets
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AMD EPYC 7601, GCC10, no LTO |
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Haswell 4 GHz, GCC10 LTO |
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AMD EPYC 7501 2 GHz, GCC10 no-LTO |
axic
reviewed
Nov 5, 2020
| (block | ||
| (br_table 3 2 1 0 4 (get_local 0)) | ||
| (return (i32.const 99)) | ||
| (return (i32.const 0x41)) |
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Any particular reason these were renumbered? Just to make it easier to read below?
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I first converted them to hex to easier find them in the bytecode, but this seem not relevant any more.
axic
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Nov 5, 2020
| if (!module.has_memory()) | ||
| throw validation_error{"memory instructions require imported or defined memory"}; | ||
| break; | ||
| continue; |
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Is this continue here jumping to the while body? I did not know you can jump out from within switches with it.
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This is a bit hackish, but also "minimal" change. The continue only affects loops but break both loops and switches.
axic
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Nov 5, 2020
| uint32_t offset; | ||
| std::tie(offset, pos) = leb128u_decode<uint32_t>(pos, end); | ||
| push(code.immediates, offset); | ||
| code.instructions.push_back(opcode); |
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Btw, why is the old code (end of loop) using emplace_back(opcode) but the new commits are not?
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The std::string only has .push_back(). It will be easier to try this instead of std::vector.
axic
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Nov 5, 2020
| ASSERT_EQ(module->codesec[0].immediates.substr(4), "00000000"_bytes); // load offset. | ||
| auto* const load_instr = const_cast<uint8_t*>(&module->codesec[0].instructions[1]); | ||
| ASSERT_EQ(*load_instr, Instr::i32_load); | ||
| ASSERT_EQ(bytes_view(load_instr + 1, 4), "00000000"_bytes); // load offset. |
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Is this bytes_view alternative better because it is faster, or does it result in a nicer error display?
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I think it was easier for me to read it like that when modifying the test.
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test/unittests/parser_expr_test.cpp
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| "00000000"_bytes; // stack_drop | ||
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| EXPECT_EQ(code.immediates.substr(br_table_imm_offset, expected_br_imm.size()), expected_br_imm); | ||
| EXPECT_EQ(code.immediates.substr(0, expected_br_imm.size()), expected_br_imm); |
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Ah the old immediates table here skipped the local for some reason.
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This test always takes the part of the immediates for the br_table only. Now this part starts at 0 because we removed other immediates. I didn't bother to keep the br_table_imm_offset name. In the end when all immediates are move to instructions we check all bytes anyway.
axic
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Nov 5, 2020
| const auto [code, pos] = parse_expr(code1_bin, 0, {}, module); | ||
| EXPECT_THAT(code.instructions, | ||
| ElementsAre(Instr::i32_const, 0, 0, 0, 0, Instr::call_indirect, Instr::end)); | ||
| ElementsAre(Instr::i32_const, 0, 0, 0, 0, Instr::call_indirect, 0, 0, 0, 0, Instr::end)); |
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Is there really a single test affected by call immediates?
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It looks like. All intermediate commits should pass all tests. Immediates for calls are rather simple and at that time we were writing more wat2wasm tests.
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Nov 5, 2020
test/unittests/parser_test.cpp
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| ElementsAre(Instr::local_get, 0, 0, 0, 0, Instr::local_get, 1, 0, 0, 0, Instr::i32_add, | ||
| Instr::local_get, 2, 0, 0, 0, Instr::i32_add, Instr::local_tee, 2, 0, 0, 0, | ||
| Instr::local_get, 0, 0, 0, 0, Instr::i32_add, Instr::end)); | ||
| EXPECT_EQ(c.immediates.size(), 0); |
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Actually it would have been nice to have the final "remove immediates from struct" as a separate commit to see the impact of changes.
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Co-authored-by: Paweł Bylica <[email protected]>
This also drop the immediates array as no longer needed.
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axic
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Nov 6, 2020
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