cmd/compile: better check for single live memory

Enhance the one-live-memory-at-a-time check to run during many
more phases of the SSA backend. Also make it work in an interblock
fashion.

Change types.IsMemory to return true for tuples containing a memory type.

Fix trim pass to build the merged phi correctly. Doesn't affect
code but allows the check to pass after trim runs.

Switch the AddTuple* ops to take the memory-containing tuple argument second.

Update #20335

Change-Id: I5b03ef3606b75a9e4f765276bb8b183cdc172b43
Reviewed-on: https://go-review.googlesource.com/43495
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

1 files changed, 17 insertions, 3 deletions

diff --git a/src/cmd/compile/internal/ssa/trim.go b/src/cmd/compile/internal/ssa/trim.go
index 09e80bdfe5..04b4fd4d54 100644
--- a/src/cmd/compile/internal/ssa/trim.go
+++ b/src/cmd/compile/internal/ssa/trim.go
@@ -46,10 +46,24 @@ func trim(f *Func) {
 						v.resetArgs()
 						continue
 					}
-					// Pad the arguments of the remaining phi-ops, so
+					// Pad the arguments of the remaining phi-ops so
 					// they match the new predecessor count of `s`.
-					for len(v.Args) < len(s.Preds) {
-						v.AddArg(v.Args[0])
+					// Since s did not have a Phi op corresponding to
+					// the phi op in b, the other edges coming into s
+					// must be loopback edges from s, so v is the right
+					// argument to v!
+					args := make([]*Value, len(v.Args))
+					copy(args, v.Args)
+					v.resetArgs()
+					for x := 0; x < j; x++ {
+						v.AddArg(v)
+					}
+					v.AddArg(args[0])
+					for x := j + 1; x < ns; x++ {
+						v.AddArg(v)
+					}
+					for _, a := range args[1:] {
+						v.AddArg(a)
 					}
 				}
 				b.Values[k] = v