cmd/compile: prevent IsNewObject from taking quadratic time
As part of IsNewObject, we need to go from the SelectN[0] use of
a call to the SelectN[1] use of a call. The current code does this
by just looking through the block. If the block is very large,
this ends up taking quadratic time.
Instead, prepopulate a map from call -> SelectN[1] user of that call.
That lets us find the SelectN[1] user in constant time.
Fixes #57657
Change-Id: Ie2e0b660af5c080314f4f17ba2838510a1147f9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/461080
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Keith Randall <khr@golang.org> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>