cmd/compile: avoid generating duplicated in-register Arg

In expand_calls, when rewriting OpArg to OpArgIntReg/OpArgFloatReg,
avoid generating duplicates. Otherwise it will confuse the
register allocator: it would think the second occurance clobbers
the first's register, causing it to generate copies, which may
clobber other args.

Change-Id: I4f1dc0519afb77500eae1c0e6ac8745e51f7aa4e
Reviewed-on: https://go-review.googlesource.com/c/go/+/306029
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -1378,6 +1378,11 @@ func expandCalls(f *Func) {
 // rewriteArgToMemOrRegs converts OpArg v in-place into the register version of v,
 // if that is appropriate.
 func (x *expandState) rewriteArgToMemOrRegs(v *Value) *Value {
+	if x.debug {
+		x.indent(3)
+		defer x.indent(-3)
+		x.Printf("rewriteArgToMemOrRegs(%s)\n", v.LongString())
+	}
 	pa := x.prAssignForArg(v)
 	switch len(pa.Registers) {
 	case 0:
@@ -1387,15 +1392,26 @@ func (x *expandState) rewriteArgToMemOrRegs(v *Value) *Value {
 				pa.Offset(), frameOff, v.LongString()))
 		}
 	case 1:
+		t := v.Type
+		key := selKey{v, 0, t.Width, t}
+		w := x.commonArgs[key]
+		if w != nil {
+			v.copyOf(w)
+			break
+		}
 		r := pa.Registers[0]
 		var i int64
 		v.Op, i = ArgOpAndRegisterFor(r, x.f.ABISelf)
 		v.Aux = &AuxNameOffset{v.Aux.(*ir.Name), 0}
 		v.AuxInt = i
+		x.commonArgs[key] = v
 
 	default:
 		panic(badVal("Saw unexpanded OpArg", v))
 	}
+	if x.debug {
+		x.Printf("-->%s\n", v.LongString())
+	}
 	return v
 }
 

test/abi/store_reg_args.go

@@ -0,0 +1,29 @@
+// run
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// When the function Store an Arg and also use it in another place,
+// be sure not to generate duplicated OpArgXXXReg values, which confuses
+// the register allocator.
+
+package main
+
+//go:noinline
+//go:registerparams
+func F(x, y float32) {
+	if x < 0 {
+		panic("FAIL")
+	}
+	g = [4]float32{x, y, x, y}
+}
+
+var g [4]float32
+
+func main() {
+	F(1, 2)
+	if g[0] != 1 || g[1] != 2 || g[2] != 1 || g[3] != 2 {
+		panic("FAIL")
+	}
+}