If an expression is addressable, we compute its address then load, rather than
extracting the value of subelements. For aggregates this avoids large copies.
Example:
var x [2]struct{y [3]int}
print(x[1].y[2])
Was:
t0 = local [3]struct{x [5]int} (x) *[3]struct{x [5]int}
t1 = *t0 [3]struct{x [5]int}
t2 = t1[1:int] struct{x [5]int}
t3 = t2.x [#0] [5]int
t4 = t3[2:int] int
Now:
t1 = &t0[1:int] *struct{x [5]int}
t2 = &t1.x [#0] *[5]int
t3 = &t2[2:int] *int
t4 = *t3 int
Also:
- make emitFieldSelections responsible for calling emitDebugRef, as
one of its two calls was forgetting to do it.
- relax the specification of (*Program).VarValue because not all
subexpressions are materalized as values now.
- fix up the objlookup.go test expectations to match.
go/ssa/interp test runs 10% faster.
Thanks to Peter Collingbourne for pointing this out.
LGTM=pcc
R=pcc, gri
CC=golang-codereviews
https://golang.org/cl/109710043
514bdfb1b7