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cmd/compile: fix magic multiply smashing AX

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Fixes #12411.

Change-Id: I2202a754c7750e3b2119e3744362c98ca0d2433e
Reviewed-on: https://go-review.googlesource.com/17818
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Russ Cox 2015-12-14 15:55:44 -05:00
parent 63a6f305ef
commit 03c8164849
3 changed files with 44 additions and 20 deletions
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19
src/cmd/compile/internal/amd64/ggen.go
View file

@ -365,24 +365,25 @@ func cgen_hmul(nl *gc.Node, nr *gc.Node, res *gc.Node) {
gc.Cgenr(nl, &n1, res)
var n2 gc.Node
gc.Cgenr(nr, &n2, nil)
var ax gc.Node
gc.Nodreg(&ax, t, x86.REG_AX)
var ax, oldax, dx, olddx gc.Node
savex(x86.REG_AX, &ax, &oldax, res, gc.Types[gc.TUINT64])
savex(x86.REG_DX, &dx, &olddx, res, gc.Types[gc.TUINT64])
gmove(&n1, &ax)
gins(a, &n2, nil)
gc.Regfree(&n2)
gc.Regfree(&n1)
var dx gc.Node
if t.Width == 1 {
// byte multiply behaves differently.
gc.Nodreg(&ax, t, x86.REG_AH)
gc.Nodreg(&dx, t, x86.REG_DX)
gmove(&ax, &dx)
var byteAH, byteDX gc.Node
gc.Nodreg(&byteAH, t, x86.REG_AH)
gc.Nodreg(&byteDX, t, x86.REG_DX)
gmove(&byteAH, &byteDX)
}
gc.Nodreg(&dx, t, x86.REG_DX)
gmove(&dx, res)
restx(&ax, &oldax)
restx(&dx, &olddx)
}
/*

21
src/cmd/compile/internal/x86/ggen.go
View file

@ -531,24 +531,21 @@ func cgen_bmul(op gc.Op, nl *gc.Node, nr *gc.Node, res *gc.Node) bool {
func cgen_hmul(nl *gc.Node, nr *gc.Node, res *gc.Node) {
var n1 gc.Node
var n2 gc.Node
var ax gc.Node
var dx gc.Node
t := nl.Type
a := optoas(gc.OHMUL, t)
// gen nl in n1.
gc.Tempname(&n1, t)
gc.Cgen(nl, &n1)
// gen nr in n2.
gc.Regalloc(&n2, t, res)
gc.Cgen(nr, &n2)
// multiply.
gc.Nodreg(&ax, t, x86.REG_AX)
var ax, oldax, dx, olddx gc.Node
savex(x86.REG_AX, &ax, &oldax, res, gc.Types[gc.TUINT32])
savex(x86.REG_DX, &dx, &olddx, res, gc.Types[gc.TUINT32])
gmove(&n2, &ax)
gins(a, &n1, nil)
@ -556,14 +553,16 @@ func cgen_hmul(nl *gc.Node, nr *gc.Node, res *gc.Node) {
if t.Width == 1 {
// byte multiply behaves differently.
gc.Nodreg(&ax, t, x86.REG_AH)
gc.Nodreg(&dx, t, x86.REG_DX)
gmove(&ax, &dx)
var byteAH, byteDX gc.Node
gc.Nodreg(&byteAH, t, x86.REG_AH)
gc.Nodreg(&byteDX, t, x86.REG_DX)
gmove(&byteAH, &byteDX)
}
gc.Nodreg(&dx, t, x86.REG_DX)
gmove(&dx, res)
restx(&ax, &oldax)
restx(&dx, &olddx)
}
/*

24
test/fixedbugs/issue12411.go Normal file
View file

@ -0,0 +1,24 @@
// +build !386
// run
// Copyright 2015 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.
// Issue 12411. Loss of AX during %.
package main
func main() {
x := f(4)
if x != 0 {
println("BUG: x=", x)
}
}
//go:noinline
func f(x int) int {
// AX was live on entry to one of the % code generations,
// and the % code generation smashed it.
return ((2 * x) % 3) % (2 % ((x << 2) ^ (x % 3)))
}