cmd/compile: make amd64 version of zerorange regabi-friendly

Change the amd64 version of 'zerorange' to avoid using RAX/RDI, since
it can be called in a context when one of these registers is live
(contains an incoming parameter).

Updates #40724.

Change-Id: Ibfa2b4e156b876354d4f8bd04eb8773c7056d948
Reviewed-on: https://go-review.googlesource.com/c/go/+/305829
Trust: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 19 insertions, 13 deletions

diff --git a/src/cmd/compile/internal/amd64/ggen.go b/src/cmd/compile/internal/amd64/ggen.go
index 259a083f75..e56ec90dc8 100644
--- a/src/cmd/compile/internal/amd64/ggen.go
+++ b/src/cmd/compile/internal/amd64/ggen.go
@@ -56,7 +56,7 @@ func dzDI(b int64) int64 {
 
 func zerorange(pp *objw.Progs, p *obj.Prog, off, cnt int64, state *uint32) *obj.Prog {
 	const (
-		ax  = 1 << iota // if AX is already zeroed.
+		r13 = 1 << iota // if R13 is already zeroed.
 		x15             // if X15 is already zeroed. Note: in new ABI, X15 is always zero.
 	)
 
@@ -69,21 +69,21 @@ func zerorange(pp *objw.Progs, p *obj.Prog, off, cnt int64, state *uint32) *obj.
 		if cnt%int64(types.PtrSize) != 0 {
 			base.Fatalf("zerorange count not a multiple of widthptr %d", cnt)
 		}
-		if *state&ax == 0 {
-			p = pp.Append(p, x86.AMOVQ, obj.TYPE_CONST, 0, 0, obj.TYPE_REG, x86.REG_AX, 0)
-			*state |= ax
+		if *state&r13 == 0 {
+			p = pp.Append(p, x86.AMOVQ, obj.TYPE_CONST, 0, 0, obj.TYPE_REG, x86.REG_R13, 0)
+			*state |= r13
 		}
-		p = pp.Append(p, x86.AMOVL, obj.TYPE_REG, x86.REG_AX, 0, obj.TYPE_MEM, x86.REG_SP, off)
+		p = pp.Append(p, x86.AMOVL, obj.TYPE_REG, x86.REG_R13, 0, obj.TYPE_MEM, x86.REG_SP, off)
 		off += int64(types.PtrSize)
 		cnt -= int64(types.PtrSize)
 	}
 
 	if cnt == 8 {
-		if *state&ax == 0 {
-			p = pp.Append(p, x86.AMOVQ, obj.TYPE_CONST, 0, 0, obj.TYPE_REG, x86.REG_AX, 0)
-			*state |= ax
+		if *state&r13 == 0 {
+			p = pp.Append(p, x86.AMOVQ, obj.TYPE_CONST, 0, 0, obj.TYPE_REG, x86.REG_R13, 0)
+			*state |= r13
 		}
-		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_AX, 0, obj.TYPE_MEM, x86.REG_SP, off)
+		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_R13, 0, obj.TYPE_MEM, x86.REG_SP, off)
 	} else if !isPlan9 && cnt <= int64(8*types.RegSize) {
 		if !objabi.Experiment.RegabiG && *state&x15 == 0 {
 			p = pp.Append(p, x86.AXORPS, obj.TYPE_REG, x86.REG_X15, 0, obj.TYPE_REG, x86.REG_X15, 0)
@@ -102,17 +102,23 @@ func zerorange(pp *objw.Progs, p *obj.Prog, off, cnt int64, state *uint32) *obj.
 			p = pp.Append(p, x86.AXORPS, obj.TYPE_REG, x86.REG_X15, 0, obj.TYPE_REG, x86.REG_X15, 0)
 			*state |= x15
 		}
+		// Save DI to r12. With the amd64 Go register abi, DI can contain
+		// an incoming parameter, whereas R12 is always scratch.
+		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_DI, 0, obj.TYPE_REG, x86.REG_R12, 0)
+		// Emit duffzero call
 		p = pp.Append(p, leaptr, obj.TYPE_MEM, x86.REG_SP, off+dzDI(cnt), obj.TYPE_REG, x86.REG_DI, 0)
 		p = pp.Append(p, obj.ADUFFZERO, obj.TYPE_NONE, 0, 0, obj.TYPE_ADDR, 0, dzOff(cnt))
 		p.To.Sym = ir.Syms.Duffzero
-
 		if cnt%16 != 0 {
 			p = pp.Append(p, x86.AMOVUPS, obj.TYPE_REG, x86.REG_X15, 0, obj.TYPE_MEM, x86.REG_DI, -int64(8))
 		}
+		// Restore DI from r12
+		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_R12, 0, obj.TYPE_REG, x86.REG_DI, 0)
+
 	} else {
-		if *state&ax == 0 {
-			p = pp.Append(p, x86.AMOVQ, obj.TYPE_CONST, 0, 0, obj.TYPE_REG, x86.REG_AX, 0)
-			*state |= ax
+		if *state&r13 == 0 {
+			p = pp.Append(p, x86.AMOVQ, obj.TYPE_CONST, 0, 0, obj.TYPE_REG, x86.REG_R13, 0)
+			*state |= r13
 		}
 
 		p = pp.Append(p, x86.AMOVQ, obj.TYPE_CONST, 0, cnt/int64(types.RegSize), obj.TYPE_REG, x86.REG_CX, 0)