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
Blocks dominated by "if false" should be retained in the
initial SSA form so they remain visible to subsequent source
code analysis tools.
In any case, true compilers already need a stronger version of
this optimization so they can simplify CFGs such as this:
const x, y = ...
switch x {case y:...}
where a branch is constant but the comparison of constants
does not occur within an expression.
LGTM=gri
R=gri
CC=golang-codereviews, pcc
https://golang.org/cl/101250043
An identifier X in anonymous struct field struct{X} is both a
definition of a field (*Var) and reference to a type
(*TypeName). Now that we have split the map, we can capture
both of these aspects.
Interestingly, every client but one was going to extra effort
to iterate over just the uses or just the defs; this
simplifies them.
Also, fix two bug related to tagless switches:
- An entry was being recorded in the Object map for a piece of
synthetic syntax.
- The "true" identifier was being looked up in the current scope,
which allowed perverse users to locally redefine it. Now
we use the bool (not untyped boolean) constant true, per the
consequent clarification of the spec (issue 7404).
+ tests.
Fixesgolang/go#7276
LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/68270044
Ian Cottrell
Alan Donovan