cmd/compile/internal/arm64: remove Reginuse check in clearfat

Fixes golang/go#12133

CL 13630 fixed the use of a stale reg[] array in the various arch
backends which was causing the check in clearfat to pass
unconditionally on arm64.

With this check fixed, arm64 now considers REGRT1 to always be in use
as it is part of the reserved register set, see arm64/gsubr.go.

However, ppc64 does not consider REGRT1 and REGRT2 to be part of its
reserved set, so its identical clearfat check passes.

This CL removes the Reginuse check inside clearfat as REGRT1 is
guarenteed always be free on arm64.

Change-Id: I4719150d3c3378fae155b863c474529df18d4c17
Reviewed-on: https://go-review.googlesource.com/13650
Reviewed-by: Russ Cox <rsc@golang.org>

diff --git a/src/cmd/compile/internal/arm64/ggen.go b/src/cmd/compile/internal/arm64/ggen.go
index ff223087a105de290199bba7ee878c137fcd2fd2..cba4d991513216120dbeb13baa129daf0fd77fad 100644 (file)
--- a/src/cmd/compile/internal/arm64/ggen.go
+++ b/src/cmd/compile/internal/arm64/ggen.go
@@ -418,15 +418,12 @@ func clearfat(nl *gc.Node) {
        c := uint64(w % 8) // bytes
        q := uint64(w / 8) // dwords
 
-       if gc.GetReg(arm64.REGRT1) > 0 {
-               gc.Fatal("R%d in use during clearfat", arm64.REGRT1-arm64.REG_R0)
-       }
-
        var r0 gc.Node
        gc.Nodreg(&r0, gc.Types[gc.TUINT64], arm64.REGZERO)
        var dst gc.Node
+
+       // REGRT1 is reserved on arm64, see arm64/gsubr.go.
        gc.Nodreg(&dst, gc.Types[gc.Tptr], arm64.REGRT1)
-       gc.SetReg(arm64.REGRT1, gc.GetReg(arm64.REGRT1)+1)
        gc.Agen(nl, &dst)
 
        var boff uint64
@@ -484,8 +481,6 @@ func clearfat(nl *gc.Node) {
                p.To.Type = obj.TYPE_MEM
                p.To.Offset = int64(t + boff)
        }
-
-       gc.SetReg(arm64.REGRT1, gc.GetReg(arm64.REGRT1)-1)
 }
 
 // Called after regopt and peep have run.