cmd/compile: handle rematerialized op for incompatible reg constraint

This CL fixes an issue raised by contributor dominikh@.

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: I941b330a6ba6f6c120c69951ddd24933f2f0b3ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/704056
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/708861

diff --git a/src/cmd/compile/internal/ssa/regalloc.go b/src/cmd/compile/internal/ssa/regalloc.go
index 26c742d7fe78ffa2f89d644a6a0c512627a69992..88861dfa14c8408aa6d2914a3359307d381629a7 100644 (file)
--- a/src/cmd/compile/internal/ssa/regalloc.go
+++ b/src/cmd/compile/internal/ssa/regalloc.go
@@ -2561,7 +2561,26 @@ func (e *edgeState) processDest(loc Location, vid ID, splice **Value, pos src.XP
                        e.s.f.Fatalf("can't find source for %s->%s: %s\n", e.p, e.b, v.LongString())
                }
                if dstReg {
-                       x = v.copyInto(e.p)
+                       // Handle incompatible registers.
+                       // For #70451.
+                       if e.s.regspec(v).outputs[0].regs&regMask(1<<register(loc.(*Register).num)) == 0 && c != nil {
+                               _, srcReg := src.(*Register)
+                               if !srcReg {
+                                       // We need a tmp register
+                                       x = v.copyInto(e.p)
+                                       r := e.findRegFor(x.Type)
+                                       e.erase(r)
+                                       // Rematerialize to a tmp register
+                                       e.set(r, vid, x, false, pos)
+                                       // Copy from tmp to the desired register
+                                       x = e.p.NewValue1(pos, OpCopy, x.Type, x)
+                               } else {
+                                       // It exist in a valid register already, so just copy it to the desired register
+                                       x = e.p.NewValue1(pos, OpCopy, c.Type, c)
+                               }
+                       } else {
+                               x = v.copyInto(e.p)
+                       }
                } else {
                        // Rematerialize into stack slot. Need a free
                        // register to accomplish this.