From fcd482a2d014137d8c20bf02bcc8fe37b107eb8c Mon Sep 17 00:00:00 2001 From: Cherry Mui Date: Tue, 18 Jan 2022 18:36:00 -0500 Subject: [release-branch.go1.16] cmd/compile: don't elide extension for LoadReg to FP register on MIPS64 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 #50682. Change-Id: Id8991df78d5acdecd3fd6138c558428cbd5f6ba3 Reviewed-on: https://go-review.googlesource.com/c/go/+/379236 Trust: Cherry Mui Run-TryBot: Cherry Mui TryBot-Result: Gopher Robot Reviewed-by: David Chase (cherry picked from commit d93ff73ae207763871bee38590242be968b2e743) Reviewed-on: https://go-review.googlesource.com/c/go/+/379515 --- src/cmd/compile/internal/mips64/ssa.go | 5 ++++- test/fixedbugs/issue50671.go | 35 ++++++++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+), 1 deletion(-) create mode 100644 test/fixedbugs/issue50671.go diff --git a/src/cmd/compile/internal/mips64/ssa.go b/src/cmd/compile/internal/mips64/ssa.go index 2727c4d8a8..b0e0165ad8 100644 --- a/src/cmd/compile/internal/mips64/ssa.go +++ b/src/cmd/compile/internal/mips64/ssa.go @@ -321,7 +321,10 @@ func ssaGenValue(s *gc.SSAGenState, 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(), diff --git a/test/fixedbugs/issue50671.go b/test/fixedbugs/issue50671.go new file mode 100644 index 0000000000..9f4742bfcd --- /dev/null +++ b/test/fixedbugs/issue50671.go @@ -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") + } +} -- cgit v1.2.3-54-g00ecf