Stowage/go
2
0
Fork 0
mirror of https://github.com/golang/go.git synced 2025-12-08 06:10:04 +00:00
Code Issues Projects Releases Packages Wiki Activity

cmd/compile: fix rules regression with shifts on PPC64

Browse source 
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
Download patch file Download diff file Expand all files Collapse all files

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