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[release-branch.go1.17] cmd/compile: don't elide extension for LoadReg to FP register on MIPS64

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For an extension operation like MOVWreg, if the operand is already
extended, we optimize the second extension out. Usually a LoadReg
of a proper type would come already extended, as a MOVW/MOVWU etc.
instruction does. But for a LoadReg to a floating point register,
the instruction does not do the extension. So we cannot elide the
extension.

Updates #50671.
Fixes #50683.

Change-Id: Id8991df78d5acdecd3fd6138c558428cbd5f6ba3
Reviewed-on: https://go-review.googlesource.com/c/go/+/379236
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
(cherry picked from commit d93ff73ae2)
Reviewed-on: https://go-review.googlesource.com/c/go/+/379514
This commit is contained in:
Cherry Mui 2022-01-18 18:36:00 -05:00
parent 17e179e187
commit 1651426f77
2 changed files with 39 additions and 1 deletions
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5
src/cmd/compile/internal/mips64/ssa.go
View File

@ -320,7 +320,10 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
for a.Op == ssa.OpCopy || a.Op == ssa.OpMIPS64MOVVreg {
a = a.Args[0]
}
if a.Op == ssa.OpLoadReg {
if a.Op == ssa.OpLoadReg && mips.REG_R0 <= a.Reg() && a.Reg() <= mips.REG_R31 {
// LoadReg from a narrower type does an extension, except loading
// to a floating point register. So only eliminate the extension
// if it is loaded to an integer register.
t := a.Type
switch {
case v.Op == ssa.OpMIPS64MOVBreg && t.Size() == 1 && t.IsSigned(),

35
test/fixedbugs/issue50671.go Normal file
View File

@ -0,0 +1,35 @@
// run
// Copyright 2022 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 50671: sign extension eliminated incorrectly on MIPS64.
package main
//go:noinline
func F(x int32) (float64, int64) {
a := float64(x)
b := int64(x)
return a, b
}
var a, b, c float64
// Poison some floating point registers with non-zero high bits.
//
//go:noinline
func poison(x float64) {
a = x - 123.45
b = a * 1.2
c = b + 3.4
}
func main() {
poison(333.3)
_, b := F(123)
if b != 123 {
panic("FAIL")
}
}