cmd/compile: fix outgoing calls with GOEXPERIMENT=regabiargs

The logic for constructing calls in (*state).call is based around
targeted experiments with register-based calls. However, when the
register ABI is turned on everywhere, it currently doesn't account for
direct calls to non-ABIInternal functions. This CL adds a much simpler
path to (*state).call when regabiargs is turned on that looks at the
ABI of the target function.

For #40724.

Change-Id: I7f4f5fed8a5ec131bcf1ce5b9d94d45672a304cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/306410
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -4854,21 +4854,24 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 	var ACArgs []*types.Type    // AuxCall args
 	var ACResults []*types.Type // AuxCall results
 	var callArgs []*ssa.Value   // For late-expansion, the args themselves (not stored, args to the call instead).
-	inRegistersForTesting := false // If a call uses register ABI for one of the testing reasons, pragma, magic types, magic names
 
+	callABI := s.f.ABIDefault
+
+	if !objabi.Experiment.RegabiArgs {
 		var magicFnNameSym *types.Sym
 		if fn.Name() != nil {
 			magicFnNameSym = fn.Name().Sym()
 			ss := magicFnNameSym.Name
 			if strings.HasSuffix(ss, magicNameDotSuffix) {
-			inRegistersForTesting = true
+				callABI = s.f.ABI1
 			}
 		}
 		if magicFnNameSym == nil && n.Op() == ir.OCALLINTER {
 			magicFnNameSym = fn.(*ir.SelectorExpr).Sym()
 			ss := magicFnNameSym.Name
 			if strings.HasSuffix(ss, magicNameDotSuffix[1:]) {
-			inRegistersForTesting = true
+				callABI = s.f.ABI1
+			}
 		}
 	}
 
@@ -4881,10 +4884,23 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		if k == callNormal && fn.Op() == ir.ONAME && fn.(*ir.Name).Class == ir.PFUNC {
 			fn := fn.(*ir.Name)
 			callee = fn
+			if objabi.Experiment.RegabiArgs {
+				// This is a static call, so it may be
+				// a direct call to a non-ABIInternal
+				// function. fn.Func may be nil for
+				// some compiler-generated functions,
+				// but those are all ABIInternal.
+				if fn.Func != nil {
+					callABI = abiForFunc(fn.Func, s.f.ABI0, s.f.ABI1)
+				}
+			} else {
 				// TODO(register args) remove after register abi is working
 				inRegistersImported := fn.Pragma()&ir.RegisterParams != 0
 				inRegistersSamePackage := fn.Func != nil && fn.Func.Pragma&ir.RegisterParams != 0
-			inRegistersForTesting = inRegistersForTesting || inRegistersImported || inRegistersSamePackage
+				if inRegistersImported || inRegistersSamePackage {
+					callABI = s.f.ABI1
+				}
+			}
 			break
 		}
 		closure = s.expr(fn)
@@ -4909,15 +4925,12 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		}
 	}
 
+	if !objabi.Experiment.RegabiArgs {
 		if regAbiForFuncType(n.X.Type().FuncType()) {
 			// Magic last type in input args to call
-		inRegistersForTesting = true
-	}
-
-	callABI := s.f.ABIDefault
-	if inRegistersForTesting {
 			callABI = s.f.ABI1
 		}
+	}
 
 	params := callABI.ABIAnalyze(n.X.Type(), false /* Do not set (register) nNames from caller side -- can cause races. */)
 	types.CalcSize(fn.Type())