5ae8575296
* x64: Take SIGFPE signals for divide traps Prior to this commit Wasmtime would configure `avoid_div_traps=true` unconditionally for Cranelift. This, for the division-based instructions, would change emitted code to explicitly trap on trap conditions instead of letting the `div` x86 instruction trap. There's no specific reason for Wasmtime, however, to specifically avoid traps in the `div` instruction. This means that the extra generated branches on x86 aren't necessary since the `div` and `idiv` instructions already trap for similar conditions as wasm requires. This commit instead disables the `avoid_div_traps` setting for Wasmtime's usage of Cranelift. Subsequently the codegen rules were updated slightly: * When `avoid_div_traps=true`, traps are no longer emitted for `div` instructions. * The `udiv`/`urem` instructions now list their trap as divide-by-zero instead of integer overflow. * The lowering for `sdiv` was updated to still explicitly check for zero but the integer overflow case is deferred to the instruction itself. * The lowering of `srem` no longer checks for zero and the listed trap for the `div` instruction is a divide-by-zero. This means that the codegen for `udiv` and `urem` no longer have any branches. The codegen for `sdiv` removes one branch but keeps the zero-check to differentiate the two kinds of traps. The codegen for `srem` removes one branch but keeps the -1 check since the semantics of `srem` mismatch with the semantics of `idiv` with a -1 divisor (specifically for INT_MIN). This is unlikely to have really all that much of a speedup but was something I noticed during #6008 which seemed like it'd be good to clean up. Plus Wasmtime's signal handling was already set up to catch `SIGFPE`, it was just never firing. * Remove the `avoid_div_traps` cranelift setting With no known users currently removing this should be possible and helps simplify the x64 backend. * x64: GC more support for avoid_div_traps Remove the `validate_sdiv_divisor*` pseudo-instructions and clean up some of the ISLE rules now that `div` is allowed to itself trap unconditionally. * x64: Store div trap code in instruction itself * Keep divisors in registers, not in memory Don't accidentally fold multiple traps together * Handle EXC_ARITHMETIC on macos * Update emit tests * Update winch and tests
25 lines
819 B
Plaintext
25 lines
819 B
Plaintext
;;! target = "x86_64"
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(module
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(func (param i64) (param i64) (result i64)
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(local.get 0)
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(local.get 1)
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(i64.div_s)
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)
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)
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;; 0: 55 push rbp
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;; 1: 4889e5 mov rbp, rsp
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;; 4: 4883ec10 sub rsp, 0x10
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;; 8: 48897c2408 mov qword ptr [rsp + 8], rdi
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;; d: 48893424 mov qword ptr [rsp], rsi
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;; 11: 488b0c24 mov rcx, qword ptr [rsp]
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;; 15: 488b442408 mov rax, qword ptr [rsp + 8]
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;; 1a: 4883f900 cmp rcx, 0
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;; 1e: 0f8502000000 jne 0x26
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;; 24: 0f0b ud2
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;; 26: 4899 cqo
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;; 28: 48f7f9 idiv rcx
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;; 2b: 4883c410 add rsp, 0x10
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;; 2f: 5d pop rbp
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;; 30: c3 ret
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