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cmd/compile: fix rules regression with shifts on PPC64

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Some rules for PPC64 were checking for a case
where a shift followed by an 'and' of a mask could
be lowered, depending on the format of the mask. The
function to verify if the mask was valid for this purpose
was not checking if the mask was 0 which we don't want to
allow. This case can happen if previous optimizations
resulted in that mask value.

This fixes isPPC64ValidShiftMask to check for a mask of 0 and return
false.

This also adds a codegen testcase to verify it doesn't try to
match the rules in the future.

Fixes #42610

Change-Id: I565d94e88495f51321ab365d6388c01e791b4dbb
Reviewed-on: https://go-review.googlesource.com/c/go/+/270358
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Paul Murphy <murp@ibm.com>
Reviewed-by: Carlos Eduardo Seo <carlos.seo@linaro.org>
Trust: Lynn Boger <laboger@linux.vnet.ibm.com>
This commit is contained in:
Lynn Boger 2020-11-16 09:40:45 -05:00
parent 869e2957b9
commit 0ae3b7cb74
2 changed files with 34 additions and 3 deletions
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7
src/cmd/compile/internal/ssa/rewrite.go
View file

@ -1427,10 +1427,11 @@ func DecodePPC64RotateMask(sauxint int64) (rotate, mb, me int64, mask uint64) {
return
}
// This verifies that the mask occupies the
// rightmost bits.
// This verifies that the mask is a set of
// consecutive bits including the least
// significant bit.
func isPPC64ValidShiftMask(v int64) bool {
if ((v + 1) & v) == 0 {
if (v != 0) && ((v+1)&v) == 0 {
return true
}
return false

30
test/codegen/issue42610.go Normal file
View file

@ -0,0 +1,30 @@
// asmcheck
// Copyright 2020 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.
// Don't allow 0 masks in shift lowering rules on ppc64x.
// See issue 42610.
package codegen
func f32(a []int32, i uint32) {
g := func(p int32) int32 {
i = uint32(p) * (uint32(p) & (i & 1))
return 1
}
// ppc64le: -"RLWNIM"
// ppc64: -"RLWNIM"
a[0] = g(8) >> 1
}
func f(a []int, i uint) {
g := func(p int) int {
i = uint(p) * (uint(p) & (i & 1))
return 1
}
// ppc64le: -"RLDIC"
// ppc64: -"RLDIC"
a[0] = g(8) >> 1
}