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cmd/compile: avoidable construction of stack objects #43753
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Slightly more realistic test case.
(Edit: Actually, it's an autotmp copy of |
Change https://golang.org/cl/284412 mentions this issue: |
…ng typecheck Currently, typecheck leaves arguments to OPANIC as their original type. This CL changes it to insert implicit OCONVIFACE operations to convert arguments to `interface{}` like how any other function call would be handled. No immediate benefits, other than getting to remove a tiny bit of special-case logic in order.go's handling of OPANICs. Instead, the generic code path for handling OCONVIFACE is used, if necessary. Longer term, this should be marginally helpful for #43753, as it reduces the number of cases where we need values to be addressable for runtime calls. However, this does require adding some hacks to appease existing tests: 1. We need yet another kludge in inline budgeting, to ensure that reflect.flag.mustBe stays inlinable for cmd/compile/internal/test's TestIntendedInlining. 2. Since the OCONVIFACE expressions are now being introduced during typecheck, they're now visible to escape analysis. So expressions like "panic(1)" are now seen as "panic(interface{}(1))", and escape analysis warns that the "interface{}(1)" escapes to the heap. These have always escaped to heap, just now we're accurately reporting about it. (Also, unfortunately fmt.go hides implicit conversions by default in diagnostics messages, so instead of reporting "interface{}(1) escapes to heap", it actually reports "1 escapes to heap", which is confusing. However, this confusing messaging also isn't new.) Change-Id: Icedf60e1d2e464e219441b8d1233a313770272af Reviewed-on: https://go-review.googlesource.com/c/go/+/284412 Run-TryBot: Matthew Dempsky <mdempsky@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com> Trust: Matthew Dempsky <mdempsky@google.com>
So the issue here is that during walk we end up rewriting But when we taking the address of a variable to pass it to a runtime function like mapassign, we often know the variable is going to stay live until the runtime function returns. In this case, we don't need the full generality of stack objects; instead, as long as we add VarLive ops after the call (or probably by using CallExpr.KeepAlive), then we can let liveness analysis and the stack maps take care of keeping the variable alive instead. This probably requires splitting Addrtaken into two separate flags: one to represent that the variable "needs to be addressable" and a second to represent that "the variable needs a stack object to track its liveness". We would set both flags for variables that the user takes the address of. In at least some cases in later stages of the compiler, we may only need to set "needs to be addressable". |
Change https://golang.org/cl/321711 mentions this issue: |
Change https://golang.org/cl/321712 mentions this issue: |
Change https://golang.org/cl/321714 mentions this issue: |
Change https://golang.org/cl/321713 mentions this issue: |
So all runtime map functions will use the same code path, make it easier for future CL to handle stack object for map key. Passes toolstash -cmp. For #43753 Change-Id: I374fa4e351c1eba079e2ccb637b1ef5adad1488f Reviewed-on: https://go-review.googlesource.com/c/go/+/321713 Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com> Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com> TryBot-Result: Gopher Robot <gobot@golang.org>
Compiling the program below with
-live
shows thatx
gets turned into a stack object:This is because the assignment
m[x.i] = true
passesx.i
by reference, causingx
to get marked as addrtaken.Note that the logically equivalent program that replaces
m[x.i] = true
withtmp := x.i; m[tmp] = true
does not create a stack object forx
.The text was updated successfully, but these errors were encountered: