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cmd/compile: establish regabi name/value mapping for small in-params

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When the expand_calls phase in the SSA backend lowers prolog OpArg
values into OpArgIntReg/OpArgFloatReg values, we don't always record
the assocation between the new lowered value and the parameter name.

This patch handles the simple case where a given parameter fits into
exactly one register; in this scenario it makes sense to manufacture a
new pseudo-slot for the value that points to the param, and install
the slot/value mapping in the NamedValues table for the function. More
work will be needed to deal with params that span multiple registers;
that will need to be addressed in a subsequent patch.

This change improves the parameter error rate "optargorder" benchmark
by about 7-8% (when run on the optargorder binary).

Updates #45945.

Change-Id: Ic9adbe20b6f91145d49651348818f0f5cba92b18
Reviewed-on: https://go-review.googlesource.com/c/go/+/316890
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
This commit is contained in:
Than McIntosh 2021-05-04 13:24:11 -04:00
parent 8c3d217d89
commit f62739b861
1 changed files with 15 additions and 0 deletions
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15
src/cmd/compile/internal/ssa/expand_calls.go
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@ -1714,6 +1714,21 @@ func (x *expandState) newArgToMemOrRegs(baseArg, toReplace *Value, offset int64,
} else {
w = baseArg.Block.NewValue0IA(pos, op, t, auxInt, aux)
}
// If we are creating an OpArgIntReg/OpArgFloatReg that
// corresponds to an in-param that fits entirely in a register,
// then enter it into the name/value table. The LocalSlot
// is somewhat fictitious, since there is no incoming live
// memory version of the parameter, but we need an entry in
// NamedValues in order for ssa debug tracking to include
// the value in the tracking analysis.
if len(pa.Registers) == 1 {
loc := LocalSlot{N: aux.Name, Type: t, Off: 0}
values, ok := x.f.NamedValues[loc]
if !ok {
x.f.Names = append(x.f.Names, loc)
}
x.f.NamedValues[loc] = append(values, w)
}
x.commonArgs[key] = w
if toReplace != nil {
toReplace.copyOf(w)