[dev.ssa] cmd/compile: fix phi floats

The code previously always used AX causing errors.  For now, just
switch off the type in order to at least generate valid code.

Change-Id: Iaf13120a24b62456b9b33c04ab31f2d5104b381b
Reviewed-on: https://go-review.googlesource.com/13943Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/gc/testdata/fp_ssa.go

@@ -35,6 +35,52 @@ func manysub_ssa(a, b, c, d float64) (aa, ab, ac, ad, ba, bb, bc, bd, ca, cb, cc
 	return
 }
 
+// fpspill_ssa attempts to trigger a bug where phis with floating point values
+// were stored in non-fp registers causing an error in doasm.
+func fpspill_ssa(a int) float64 {
+	switch {
+	}
+
+	ret := -1.0
+	switch a {
+	case 0:
+		ret = 1.0
+	case 1:
+		ret = 1.1
+	case 2:
+		ret = 1.2
+	case 3:
+		ret = 1.3
+	case 4:
+		ret = 1.4
+	case 5:
+		ret = 1.5
+	case 6:
+		ret = 1.6
+	case 7:
+		ret = 1.7
+	case 8:
+		ret = 1.8
+	case 9:
+		ret = 1.9
+	case 10:
+		ret = 1.10
+	case 11:
+		ret = 1.11
+	case 12:
+		ret = 1.12
+	case 13:
+		ret = 1.13
+	case 14:
+		ret = 1.14
+	case 15:
+		ret = 1.15
+	case 16:
+		ret = 1.16
+	}
+	return ret
+}
+
 func add64_ssa(a, b float64) float64 {
 	switch {
 	}

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

@@ -550,6 +550,16 @@ func (s *regAllocState) setState(state []regState) {
 	}
 }
 
+// compatReg returns a register compatible with the a value and is used when
+// spilling/loading.
+// TODO: choose a better default register (set of reg by type?).
+func compatReg(v *Value) regMask {
+	if v.Type.IsFloat() {
+		return 1 << 16 // X0
+	}
+	return 1 << 0 // AX
+}
+
 func (s *regAllocState) regalloc(f *Func) {
 	liveset := newSparseSet(f.NumValues())
 	argset := newSparseSet(f.NumValues())
@@ -836,10 +846,11 @@ func (s *regAllocState) regalloc(f *Func) {
 				if !argset.contains(v.ID) {
 					continue
 				}
+
 				// This stack-based phi is the argument of some other
 				// phi in this block.  We must make a copy of its
 				// value so that we don't clobber it prematurely.
-				c := s.allocValToReg(v, s.values[v.ID].regs|1<<0, false)
+				c := s.allocValToReg(v, s.values[v.ID].regs|compatReg(v), false)
 				d := p.NewValue1(v.Line, OpStoreReg, v.Type, c)
 				s.values[v.ID].spill2 = d
 			}
@@ -848,9 +859,10 @@ func (s *regAllocState) regalloc(f *Func) {
 			// we might need a register to do the assignment.
 			for _, v := range stackPhis {
 				// Load phi arg into a register, then store it with a StoreReg.
-				// If already in a register, use that.  If not, use register 0.
-				// TODO: choose a better default register (set of reg by type?).
-				c := s.allocValToReg(v.Args[i], s.values[v.Args[i].ID].regs|1<<0, false)
+				// If already in a register, use that.  If not, pick a compatible
+				// register.
+				w := v.Args[i]
+				c := s.allocValToReg(w, s.values[w.ID].regs|compatReg(w), false)
 				v.Args[i] = p.NewValue1(v.Line, OpStoreReg, v.Type, c)
 			}
 			// Figure out what value goes in each register.