cmd/compile: simplify zerorange on riscv64

Drop large zeroing cases, part of removing duff support.

Change-Id: Ia2936f649901886f3eb1d7ba1f90e3bf40ea2dee
Reviewed-on: https://go-review.googlesource.com/c/go/+/697615
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Julian Zhu <[email protected]>
Reviewed-by: Mark Ryan <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Mark Freeman <[email protected]>
Reviewed-by: Joel Sing <[email protected]>

Author: mengzhuo

src/cmd/compile/internal/riscv64/ggen.go

@@ -6,54 +6,26 @@ package riscv64
 
 import (
 	"cmd/compile/internal/base"
-	"cmd/compile/internal/ir"
 	"cmd/compile/internal/objw"
 	"cmd/compile/internal/types"
 	"cmd/internal/obj"
 	"cmd/internal/obj/riscv"
 )
 
 func zeroRange(pp *objw.Progs, p *obj.Prog, off, cnt int64, _ *uint32) *obj.Prog {
-	if cnt == 0 {
-		return p
+
+	if cnt%int64(types.PtrSize) != 0 {
+		panic("zeroed region not aligned")
 	}
 
 	// Adjust the frame to account for LR.
 	off += base.Ctxt.Arch.FixedFrameSize
 
-	if cnt < int64(4*types.PtrSize) {
-		for i := int64(0); i < cnt; i += int64(types.PtrSize) {
-			p = pp.Append(p, riscv.AMOV, obj.TYPE_REG, riscv.REG_ZERO, 0, obj.TYPE_MEM, riscv.REG_SP, off+i)
-		}
-		return p
-	}
-
-	if cnt <= int64(128*types.PtrSize) {
-		p = pp.Append(p, riscv.AADDI, obj.TYPE_CONST, 0, off, obj.TYPE_REG, riscv.REG_X25, 0)
-		p.Reg = riscv.REG_SP
-		p = pp.Append(p, obj.ADUFFZERO, obj.TYPE_NONE, 0, 0, obj.TYPE_MEM, 0, 0)
-		p.To.Name = obj.NAME_EXTERN
-		p.To.Sym = ir.Syms.Duffzero
-		p.To.Offset = 8 * (128 - cnt/int64(types.PtrSize))
-		return p
+	for cnt != 0 {
+		p = pp.Append(p, riscv.AMOV, obj.TYPE_REG, riscv.REG_ZERO, 0, obj.TYPE_MEM, riscv.REG_SP, off)
+		cnt -= int64(types.PtrSize)
+		off += int64(types.PtrSize)
 	}
 
-	// Loop, zeroing pointer width bytes at a time.
-	// ADD	$(off), SP, T0
-	// ADD	$(cnt), T0, T1
-	// loop:
-	// 	MOV	ZERO, (T0)
-	// 	ADD	$Widthptr, T0
-	//	BNE	T0, T1, loop
-	p = pp.Append(p, riscv.AADD, obj.TYPE_CONST, 0, off, obj.TYPE_REG, riscv.REG_T0, 0)
-	p.Reg = riscv.REG_SP
-	p = pp.Append(p, riscv.AADD, obj.TYPE_CONST, 0, cnt, obj.TYPE_REG, riscv.REG_T1, 0)
-	p.Reg = riscv.REG_T0
-	p = pp.Append(p, riscv.AMOV, obj.TYPE_REG, riscv.REG_ZERO, 0, obj.TYPE_MEM, riscv.REG_T0, 0)
-	loop := p
-	p = pp.Append(p, riscv.AADD, obj.TYPE_CONST, 0, int64(types.PtrSize), obj.TYPE_REG, riscv.REG_T0, 0)
-	p = pp.Append(p, riscv.ABNE, obj.TYPE_REG, riscv.REG_T0, 0, obj.TYPE_BRANCH, 0, 0)
-	p.Reg = riscv.REG_T1
-	p.To.SetTarget(loop)
 	return p
 }