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cmd/compile: fix MIPS SGTconst-with-shift rules

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(SGTconst [c] (SRLconst _ [d])) && 0 <= int32(c) && uint32(d) <= 31 && 1<<(32-uint32(d)) <= int32(c) -> (MOVWconst [1])

This rule is problematic. 1<<(32-uint32(d)) <= int32(c) meant to
say that it is true if c is greater than the largest possible
value of the right shift. But when d==1, 1<<(32-1) is negative
and results in the wrong comparison.

Rewrite the rules in a more direct way.

Fixes #29402.

Change-Id: I5940fc9538d9bc3a4bcae8aa34672867540dc60e
Reviewed-on: https://go-review.googlesource.com/c/155798
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Cherry Zhang 2018-12-25 19:36:25 -05:00
parent bfaf11c158
commit 6a64efc250
5 changed files with 35 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/cmd/compile/internal/ssa/gen/MIPS.rules
View File

@ -670,8 +670,8 @@
(SGTUconst [c] (MOVHUreg _)) && 0xffff < uint32(c) -> (MOVWconst [1])
(SGTconst [c] (ANDconst [m] _)) && 0 <= int32(m) && int32(m) < int32(c) -> (MOVWconst [1])
(SGTUconst [c] (ANDconst [m] _)) && uint32(m) < uint32(c) -> (MOVWconst [1])
(SGTconst [c] (SRLconst _ [d])) && 0 <= int32(c) && uint32(d) <= 31 && 1<<(32-uint32(d)) <= int32(c) -> (MOVWconst [1])
(SGTUconst [c] (SRLconst _ [d])) && uint32(d) <= 31 && 1<<(32-uint32(d)) <= uint32(c) -> (MOVWconst [1])
(SGTconst [c] (SRLconst _ [d])) && 0 <= int32(c) && uint32(d) <= 31 && 0xffffffff>>uint32(d) < uint32(c) -> (MOVWconst [1])
(SGTUconst [c] (SRLconst _ [d])) && uint32(d) <= 31 && 0xffffffff>>uint32(d) < uint32(c) -> (MOVWconst [1])
// absorb constants into branches
(EQ (MOVWconst [0]) yes no) -> (First nil yes no)

4
src/cmd/compile/internal/ssa/gen/MIPS64.rules
View File

@ -667,8 +667,8 @@
(SGTconst [c] (MOVWUreg _)) && c < 0 -> (MOVVconst [0])
(SGTconst [c] (ANDconst [m] _)) && 0 <= m && m < c -> (MOVVconst [1])
(SGTUconst [c] (ANDconst [m] _)) && uint64(m) < uint64(c) -> (MOVVconst [1])
(SGTconst [c] (SRLVconst _ [d])) && 0 <= c && 0 < d && d <= 63 && 1<<uint64(64-d) <= c -> (MOVVconst [1])
(SGTUconst [c] (SRLVconst _ [d])) && 0 < d && d <= 63 && 1<<uint64(64-d) <= uint64(c) -> (MOVVconst [1])
(SGTconst [c] (SRLVconst _ [d])) && 0 <= c && 0 < d && d <= 63 && 0xffffffffffffffff>>uint64(d) < uint64(c) -> (MOVVconst [1])
(SGTUconst [c] (SRLVconst _ [d])) && 0 < d && d <= 63 && 0xffffffffffffffff>>uint64(d) < uint64(c) -> (MOVVconst [1])
// absorb constants into branches
(EQ (MOVVconst [0]) yes no) -> (First nil yes no)

8
src/cmd/compile/internal/ssa/rewriteMIPS.go
View File

@ -5625,7 +5625,7 @@ func rewriteValueMIPS_OpMIPSSGTUconst_0(v *Value) bool {
return true
}
// match: (SGTUconst [c] (SRLconst _ [d]))
// cond: uint32(d) <= 31 && 1<<(32-uint32(d)) <= uint32(c)
// cond: uint32(d) <= 31 && 0xffffffff>>uint32(d) < uint32(c)
// result: (MOVWconst [1])
for {
c := v.AuxInt
@ -5634,7 +5634,7 @@ func rewriteValueMIPS_OpMIPSSGTUconst_0(v *Value) bool {
break
}
d := v_0.AuxInt
if !(uint32(d) <= 31 && 1<<(32-uint32(d)) <= uint32(c)) {
if !(uint32(d) <= 31 && 0xffffffff>>uint32(d) < uint32(c)) {
break
}
v.reset(OpMIPSMOVWconst)
@ -5862,7 +5862,7 @@ func rewriteValueMIPS_OpMIPSSGTconst_10(v *Value) bool {
return true
}
// match: (SGTconst [c] (SRLconst _ [d]))
// cond: 0 <= int32(c) && uint32(d) <= 31 && 1<<(32-uint32(d)) <= int32(c)
// cond: 0 <= int32(c) && uint32(d) <= 31 && 0xffffffff>>uint32(d) < uint32(c)
// result: (MOVWconst [1])
for {
c := v.AuxInt
@ -5871,7 +5871,7 @@ func rewriteValueMIPS_OpMIPSSGTconst_10(v *Value) bool {
break
}
d := v_0.AuxInt
if !(0 <= int32(c) && uint32(d) <= 31 && 1<<(32-uint32(d)) <= int32(c)) {
if !(0 <= int32(c) && uint32(d) <= 31 && 0xffffffff>>uint32(d) < uint32(c)) {
break
}
v.reset(OpMIPSMOVWconst)

8
src/cmd/compile/internal/ssa/rewriteMIPS64.go
View File

@ -6005,7 +6005,7 @@ func rewriteValueMIPS64_OpMIPS64SGTUconst_0(v *Value) bool {
return true
}
// match: (SGTUconst [c] (SRLVconst _ [d]))
// cond: 0 < d && d <= 63 && 1<<uint64(64-d) <= uint64(c)
// cond: 0 < d && d <= 63 && 0xffffffffffffffff>>uint64(d) < uint64(c)
// result: (MOVVconst [1])
for {
c := v.AuxInt
@ -6014,7 +6014,7 @@ func rewriteValueMIPS64_OpMIPS64SGTUconst_0(v *Value) bool {
break
}
d := v_0.AuxInt
if !(0 < d && d <= 63 && 1<<uint64(64-d) <= uint64(c)) {
if !(0 < d && d <= 63 && 0xffffffffffffffff>>uint64(d) < uint64(c)) {
break
}
v.reset(OpMIPS64MOVVconst)
@ -6223,7 +6223,7 @@ func rewriteValueMIPS64_OpMIPS64SGTconst_10(v *Value) bool {
return true
}
// match: (SGTconst [c] (SRLVconst _ [d]))
// cond: 0 <= c && 0 < d && d <= 63 && 1<<uint64(64-d) <= c
// cond: 0 <= c && 0 < d && d <= 63 && 0xffffffffffffffff>>uint64(d) < uint64(c)
// result: (MOVVconst [1])
for {
c := v.AuxInt
@ -6232,7 +6232,7 @@ func rewriteValueMIPS64_OpMIPS64SGTconst_10(v *Value) bool {
break
}
d := v_0.AuxInt
if !(0 <= c && 0 < d && d <= 63 && 1<<uint64(64-d) <= c) {
if !(0 <= c && 0 < d && d <= 63 && 0xffffffffffffffff>>uint64(d) < uint64(c)) {
break
}
v.reset(OpMIPS64MOVVconst)

23
test/fixedbugs/issue29402.go Normal file
View File

@ -0,0 +1,23 @@
// run
// Copyright 2018 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 29402: wrong optimization of comparison of
// constant and shift on MIPS.
package main
//go:noinline
func F(s []int) bool {
half := len(s) / 2
return half >= 0
}
func main() {
b := F([]int{1, 2, 3, 4})
if !b {
panic("FAIL")
}
}