reflect: use global variables for register count

This change switches reflect to use global variables for ABI-related
register counts instead of internal/abi constants. The advantage of
doing so is that we can make the internal/abi constants non-zero and
enable the runtime register argument spiller/unspiller even if they're
not used. It's basically turning two things we need to flip when we
switch to the register ABI into one.

It also paves the way for testing the reflect register ABI path
independently, because now we can switch the global variables at will
and run the register-assignment algorithm in tests without having the
rest of the runtime be broken.

Change-Id: Ie23629a37a5c80aeb24909d4bd9eacbd3f0c06d9
Reviewed-on: https://go-review.googlesource.com/c/go/+/293149
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/internal/abi/abi_amd64.go b/src/internal/abi/abi_amd64.go
index 77589d4c34f32679aa6ec3f00ed83be5f4adcf4e..07c3ec1aab132ae3e74db057d1aa927be9d9d82f 100644 (file)
--- a/src/internal/abi/abi_amd64.go
+++ b/src/internal/abi/abi_amd64.go
@@ -10,16 +10,12 @@ package abi
 const (
        // See abi_generic.go.
 
-       // Currently these values are zero because whatever uses
-       // them will expect the register ABI, which isn't ready
-       // yet.
-
        // RAX, RBX, RCX, RDI, RSI, R8, R9, R10, R11.
-       IntArgRegs = 0 // 9
+       IntArgRegs = 9
 
        // X0 -> X14.
-       FloatArgRegs = 0 // 15
+       FloatArgRegs = 15
 
        // We use SSE2 registers which support 64-bit float operations.
-       EffectiveFloatRegSize = 0 // 8
+       EffectiveFloatRegSize = 8
 )

diff --git a/src/reflect/abi.go b/src/reflect/abi.go
index 36d6b3095bd8d84b88d62657d882541407bf49e0..618efd0980b726fc4f7d3487c9f237a57b4b11a1 100644 (file)
--- a/src/reflect/abi.go
+++ b/src/reflect/abi.go
@@ -9,6 +9,30 @@ import (
        "unsafe"
 )
 
+// These variables are used by the register assignment
+// algorithm in this file.
+//
+// They should be modified with care (no other reflect code
+// may be executing) and are generally only modified
+// when testing this package.
+//
+// They should never be set higher than their internal/abi
+// constant counterparts, because the system relies on a
+// structure that is at least large enough to hold the
+// registers the system supports.
+//
+// Currently they're set to zero because using the actual
+// constants will break every part of the toolchain that
+// uses reflect to call functions (e.g. go test, or anything
+// that uses text/template). The values that are currently
+// commented out there should be the actual values once
+// we're ready to use the register ABI everywhere.
+var (
+       intArgRegs   = 0          // abi.IntArgRegs
+       floatArgRegs = 0          // abi.FloatArgRegs
+       floatRegSize = uintptr(0) // uintptr(abi.EffectiveFloatRegSize)
+)
+
 // abiStep represents an ABI "instruction." Each instruction
 // describes one part of how to translate between a Go value
 // in memory and a call frame.
@@ -226,7 +250,7 @@ func (a *abiSeq) assignIntN(offset, size uintptr, n int, ptrMap uint8) bool {
        if ptrMap != 0 && size != ptrSize {
                panic("non-empty pointer map passed for non-pointer-size values")
        }
-       if a.iregs+n > abi.IntArgRegs {
+       if a.iregs+n > intArgRegs {
                return false
        }
        for i := 0; i < n; i++ {
@@ -255,7 +279,7 @@ func (a *abiSeq) assignFloatN(offset, size uintptr, n int) bool {
        if n < 0 {
                panic("invalid n")
        }
-       if a.fregs+n > abi.FloatArgRegs || abi.EffectiveFloatRegSize < size {
+       if a.fregs+n > floatArgRegs || floatRegSize < size {
                return false
        }
        for i := 0; i < n; i++ {

diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index 517c5a9d3ef91334b0c0b63bea1f7df506a44040..ddd6a5bd5b839f89877c40beedaa0ecb9005a0b7 100644 (file)
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -442,10 +442,7 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0
        MOVL    $0, DX
        JMP     runtime·morestack(SB)
 
-// REFLECTCALL_USE_REGABI is not defined. It must be defined in conjunction with the
-// register constants in the internal/abi package.
-
-#ifdef REFLECTCALL_USE_REGABI
+#ifdef GOEXPERIMENT_REGABI
 // spillArgs stores return values from registers to a *internal/abi.RegArgs in R12.
 TEXT spillArgs<>(SB),NOSPLIT,$0-0
        MOVQ AX, 0(R12)