On Wasm, the offset was not folded into LoweredAddr, so it was
not rematerializeable. This led to the address-taken operation
in some cases generated too early, before the local variable
becoming live. The liveness code thinks the variable live when
the address is taken, then backs it up to live at function
entry, then complains about it, because nothing other than
arguments should be live on entry.
This CL folds the offset into the address operation, so it is
rematerializeable and so generated right before use, after the
variable actually becomes live.
It might be possible to relax the liveness code not to think a
variable live when its address being taken, but until the address
actually being used. But it would be quite complicated. As we're
late in Go 1.11 freeze, it would be better not to do it. Also,
I think the address operation is rematerializeable now on all
architectures, so this is probably less necessary.
This may also be a slight optimization, as the address+offset is
now rematerializeable, which can be generated on the Wasm stack,
without using any "registers" which are emulated by local
variables on Wasm. I don't know how to do benchmarks on Wasm. At
least, cmd/go binary size shrinks 9K.
Fixes#25966.
Change-Id: I01e5869515d6a3942fccdcb857f924a866876e57
Reviewed-on: https://go-review.googlesource.com/120599
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Richard Musiol <neelance@gmail.com>
Go's SSA instructions only operate on registers. For example, an add
instruction would read two registers, do the addition and then write
to a register. WebAssembly's instructions, on the other hand, operate
on the stack. The add instruction first pops two values from the stack,
does the addition, then pushes the result to the stack. To fulfill
Go's semantics, one needs to map Go's single add instruction to
4 WebAssembly instructions:
- Push the value of local variable A to the stack
- Push the value of local variable B to the stack
- Do addition
- Write value from stack to local variable C
Now consider that B was set to the constant 42 before the addition:
- Push constant 42 to the stack
- Write value from stack to local variable B
This works, but is inefficient. Instead, the stack is used directly
by inlining instructions if possible. With inlining it becomes:
- Push the value of local variable A to the stack (add)
- Push constant 42 to the stack (constant)
- Do addition (add)
- Write value from stack to local variable C (add)
Note that the two SSA instructions can not be generated sequentially
anymore, because their WebAssembly instructions are interleaved.
Design doc: https://docs.google.com/document/d/131vjr4DH6JFnb-blm_uRdaC0_Nv3OUwjEY5qVCxCup4
Updates #18892
Change-Id: Ie35e1c0bebf4985fddda0d6330eb2066f9ad6dec
Reviewed-on: https://go-review.googlesource.com/103535
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit adds the wasm architecture to the compile command.
A later commit will contain the corresponding linker changes.
Design doc: https://docs.google.com/document/d/131vjr4DH6JFnb-blm_uRdaC0_Nv3OUwjEY5qVCxCup4
The following files are generated:
- src/cmd/compile/internal/ssa/opGen.go
- src/cmd/compile/internal/ssa/rewriteWasm.go
- src/cmd/internal/obj/wasm/anames.go
Updates #18892
Change-Id: Ifb4a96a3e427aac2362a1c97967d5667450fba3b
Reviewed-on: https://go-review.googlesource.com/103295
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
