[dev.ssa] cmd/compile: fix function call memory accounting

We were not recording function calls as
changing the state of memory.

As a result, the scheduler was not aware that
storing values to the stack in order to make a
function call must happen *after* retrieving
results from the stack from a just-completed
function call.

This fixes the container/ring tests.

This was my first experience debugging an issue
using the HTML output. I'm feeling quite
pleased with it.

Change-Id: I9e8276846be9fd7a60422911b11816c5175e3d0a
Reviewed-on: https://go-review.googlesource.com/13560Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/gc/ssa.go

@@ -1319,6 +1319,7 @@ func (s *state) expr(n *Node) *ssa.Value {
 
 		// read result from stack at the start of the fallthrough block
 		s.startBlock(bNext)
+		s.vars[&memvar] = call
 		var titer Iter
 		fp := Structfirst(&titer, Getoutarg(left.Type))
 		if fp == nil {