cmd/compile: use the right type for spill slot

Currently, when shuffling registers, if we need to spill a
register, we always create a spill slot of type int64. The type
doesn't actually matter, as long as it is wide enough to hold the
registers. This is no longer true with SIMD registers, which could
be wider than a int64. Create the slot with the proper type
instead.

Cherry-picked from the dev.simd branch. This CL is not
necessarily SIMD specific. Apply early to reduce risk. Test is
SIMD specific so not included for now.

Change-Id: I85c82e2532001bfdefe98c9446f2dd18583d49b4
Reviewed-on: https://go-review.googlesource.com/c/go/+/704055
TryBot-Bypass: Cherry Mui <[email protected]>
Reviewed-by: David Chase <[email protected]>
Reviewed-by: Junyang Shao <[email protected]>
Reviewed-on: https://go-review.googlesource.com/c/go/+/708860
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: cherrymui

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

@@ -2690,7 +2690,6 @@ func (e *edgeState) erase(loc Location) {
 // findRegFor finds a register we can use to make a temp copy of type typ.
 func (e *edgeState) findRegFor(typ *types.Type) Location {
 	// Which registers are possibilities.
-	types := &e.s.f.Config.Types
 	m := e.s.compatRegs(typ)
 
 	// Pick a register. In priority order:
@@ -2724,9 +2723,7 @@ func (e *edgeState) findRegFor(typ *types.Type) Location {
 				if !c.rematerializeable() {
 					x := e.p.NewValue1(c.Pos, OpStoreReg, c.Type, c)
 					// Allocate a temp location to spill a register to.
-					// The type of the slot is immaterial - it will not be live across
-					// any safepoint. Just use a type big enough to hold any register.
-					t := LocalSlot{N: e.s.f.NewLocal(c.Pos, types.Int64), Type: types.Int64}
+					t := LocalSlot{N: e.s.f.NewLocal(c.Pos, c.Type), Type: c.Type}
 					// TODO: reuse these slots. They'll need to be erased first.
 					e.set(t, vid, x, false, c.Pos)
 					if e.s.f.pass.debug > regDebug {

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

@@ -600,7 +600,7 @@ func (v *Value) removeable() bool {
 func AutoVar(v *Value) (*ir.Name, int64) {
 	if loc, ok := v.Block.Func.RegAlloc[v.ID].(LocalSlot); ok {
 		if v.Type.Size() > loc.Type.Size() {
-			v.Fatalf("spill/restore type %s doesn't fit in slot type %s", v.Type, loc.Type)
+			v.Fatalf("v%d: spill/restore type %v doesn't fit in slot type %v", v.ID, v.Type, loc.Type)
 		}
 		return loc.N, loc.Off
 	}