cmd/compile: fix incoming ABI with GOEXPERIMENT=regabiargs

When regabiargs is enabled, a function's incoming ABI should be
determined solely by the function's own definition ABI (which is
usually ABIInternal, but can be ABI0 for ABI wrappers).

For example, the current code miscompiles ABI0 -> ABIInternal wrappers
when the experiment is enabled because it treats the wrapper itself as
being called as ABIInternal. This causes it to assume the incoming
arguments are already in registers, so usually the wrapper doesn't do
anything with the arguments because it thinks they're already in the
right place. With this fix, these wrappers now correctly load the
arguments from the stack and put them in registers.

For #40724.

Change-Id: Iec784e88ebc55d9e95e830ed7533aa336f3b1ca2
Reviewed-on: https://go-review.googlesource.com/c/go/+/306409
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>

diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index 57099371e66191eb318c060b70db2ecee7c9fa0f..aaea732057a106ff63b33b56b9b102dd91aab673 100644 (file)
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -225,13 +225,26 @@ const magicNameDotSuffix = ".MagicMethodNameForTestingRegisterABI"
 const magicLastTypeName = "MagicLastTypeNameForTestingRegisterABI"
 
 // abiForFunc implements ABI policy for a function, but does not return a copy of the ABI.
-// Passing a nil function returns ABIInternal.
+// Passing a nil function returns the default ABI based on experiment configuration.
 func abiForFunc(fn *ir.Func, abi0, abi1 *abi.ABIConfig) *abi.ABIConfig {
-       a := abi1
-       if !regabiEnabledForAllCompilation() {
-               a = abi0
+       if objabi.Experiment.RegabiArgs {
+               // Select the ABI based on the function's defining ABI.
+               if fn == nil {
+                       return abi1
+               }
+               switch fn.ABI {
+               case obj.ABI0:
+                       return abi0
+               case obj.ABIInternal:
+                       // TODO(austin): Clean up the nomenclature here.
+                       // It's not clear that "abi1" is ABIInternal.
+                       return abi1
+               }
+               base.Fatalf("function %v has unknown ABI %v", fn, fn.ABI)
+               panic("not reachable")
        }
 
+       a := abi0
        if fn != nil {
                name := ir.FuncName(fn)
                magicName := strings.HasSuffix(name, magicNameDotSuffix)
@@ -263,10 +276,6 @@ func regAbiForFuncType(ft *types.Func) bool {
        return np > 0 && strings.Contains(ft.Params.FieldType(np-1).String(), magicLastTypeName)
 }
 
-func regabiEnabledForAllCompilation() bool {
-       return objabi.Experiment.RegabiArgs
-}
-
 // getParam returns the Field of ith param of node n (which is a
 // function/method/interface call), where the receiver of a method call is
 // considered as the 0th parameter. This does not include the receiver of an