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cmd/compile: fix constant folding of right shifts
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The sub-word shifts need to sign-extend before shifting, to avoid
bringing in data from higher in the argument.

Fixes #23812

Change-Id: I0a95a0b49c48f3b40b85765bb4a9bb492be0cd73
Reviewed-on: https://go-review.googlesource.com/93716
Run-TryBot: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>
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@randall77
randall77 committed Feb 14, 2018
1 parent 8de2f60 commit 755b36a
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Showing 4 changed files with 55 additions and 21 deletions.
6 changes: 3 additions & 3 deletions src/cmd/compile/internal/ssa/gen/AMD64.rules
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Original file line number Diff line number Diff line change
Expand Up @@ -1647,9 +1647,9 @@
(SUBQconst (MOVQconst [d]) [c]) -> (MOVQconst [d-c])
(SUBQconst (SUBQconst x [d]) [c]) && is32Bit(-c-d) -> (ADDQconst [-c-d] x)
(SARQconst [c] (MOVQconst [d])) -> (MOVQconst [d>>uint64(c)])
(SARLconst [c] (MOVQconst [d])) -> (MOVQconst [d>>uint64(c)])
(SARWconst [c] (MOVQconst [d])) -> (MOVQconst [d>>uint64(c)])
(SARBconst [c] (MOVQconst [d])) -> (MOVQconst [d>>uint64(c)])
(SARLconst [c] (MOVQconst [d])) -> (MOVQconst [int64(int32(d))>>uint64(c)])
(SARWconst [c] (MOVQconst [d])) -> (MOVQconst [int64(int16(d))>>uint64(c)])
(SARBconst [c] (MOVQconst [d])) -> (MOVQconst [int64(int8(d))>>uint64(c)])
(NEGQ (MOVQconst [c])) -> (MOVQconst [-c])
(NEGL (MOVLconst [c])) -> (MOVLconst [int64(int32(-c))])
(MULQconst [c] (MOVQconst [d])) -> (MOVQconst [c*d])
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24 changes: 12 additions & 12 deletions src/cmd/compile/internal/ssa/gen/AMD64Ops.go
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Original file line number Diff line number Diff line change
Expand Up @@ -270,22 +270,22 @@ func init() {
// Note: x86 is weird, the 16 and 8 byte shifts still use all 5 bits of shift amount!

{name: "SHRQ", argLength: 2, reg: gp21shift, asm: "SHRQ", resultInArg0: true, clobberFlags: true}, // unsigned arg0 >> arg1, shift amount is mod 64
{name: "SHRL", argLength: 2, reg: gp21shift, asm: "SHRL", resultInArg0: true, clobberFlags: true}, // unsigned arg0 >> arg1, shift amount is mod 32
{name: "SHRW", argLength: 2, reg: gp21shift, asm: "SHRW", resultInArg0: true, clobberFlags: true}, // unsigned arg0 >> arg1, shift amount is mod 32
{name: "SHRB", argLength: 2, reg: gp21shift, asm: "SHRB", resultInArg0: true, clobberFlags: true}, // unsigned arg0 >> arg1, shift amount is mod 32
{name: "SHRL", argLength: 2, reg: gp21shift, asm: "SHRL", resultInArg0: true, clobberFlags: true}, // unsigned uint32(arg0) >> arg1, shift amount is mod 32
{name: "SHRW", argLength: 2, reg: gp21shift, asm: "SHRW", resultInArg0: true, clobberFlags: true}, // unsigned uint16(arg0) >> arg1, shift amount is mod 32
{name: "SHRB", argLength: 2, reg: gp21shift, asm: "SHRB", resultInArg0: true, clobberFlags: true}, // unsigned uint8(arg0) >> arg1, shift amount is mod 32
{name: "SHRQconst", argLength: 1, reg: gp11, asm: "SHRQ", aux: "Int8", resultInArg0: true, clobberFlags: true}, // unsigned arg0 >> auxint, shift amount 0-63
{name: "SHRLconst", argLength: 1, reg: gp11, asm: "SHRL", aux: "Int8", resultInArg0: true, clobberFlags: true}, // unsigned arg0 >> auxint, shift amount 0-31
{name: "SHRWconst", argLength: 1, reg: gp11, asm: "SHRW", aux: "Int8", resultInArg0: true, clobberFlags: true}, // unsigned arg0 >> auxint, shift amount 0-15
{name: "SHRBconst", argLength: 1, reg: gp11, asm: "SHRB", aux: "Int8", resultInArg0: true, clobberFlags: true}, // unsigned arg0 >> auxint, shift amount 0-7
{name: "SHRLconst", argLength: 1, reg: gp11, asm: "SHRL", aux: "Int8", resultInArg0: true, clobberFlags: true}, // unsigned uint32(arg0) >> auxint, shift amount 0-31
{name: "SHRWconst", argLength: 1, reg: gp11, asm: "SHRW", aux: "Int8", resultInArg0: true, clobberFlags: true}, // unsigned uint16(arg0) >> auxint, shift amount 0-15
{name: "SHRBconst", argLength: 1, reg: gp11, asm: "SHRB", aux: "Int8", resultInArg0: true, clobberFlags: true}, // unsigned uint8(arg0) >> auxint, shift amount 0-7

{name: "SARQ", argLength: 2, reg: gp21shift, asm: "SARQ", resultInArg0: true, clobberFlags: true}, // signed arg0 >> arg1, shift amount is mod 64
{name: "SARL", argLength: 2, reg: gp21shift, asm: "SARL", resultInArg0: true, clobberFlags: true}, // signed arg0 >> arg1, shift amount is mod 32
{name: "SARW", argLength: 2, reg: gp21shift, asm: "SARW", resultInArg0: true, clobberFlags: true}, // signed arg0 >> arg1, shift amount is mod 32
{name: "SARB", argLength: 2, reg: gp21shift, asm: "SARB", resultInArg0: true, clobberFlags: true}, // signed arg0 >> arg1, shift amount is mod 32
{name: "SARL", argLength: 2, reg: gp21shift, asm: "SARL", resultInArg0: true, clobberFlags: true}, // signed int32(arg0) >> arg1, shift amount is mod 32
{name: "SARW", argLength: 2, reg: gp21shift, asm: "SARW", resultInArg0: true, clobberFlags: true}, // signed int16(arg0) >> arg1, shift amount is mod 32
{name: "SARB", argLength: 2, reg: gp21shift, asm: "SARB", resultInArg0: true, clobberFlags: true}, // signed int8(arg0) >> arg1, shift amount is mod 32
{name: "SARQconst", argLength: 1, reg: gp11, asm: "SARQ", aux: "Int8", resultInArg0: true, clobberFlags: true}, // signed arg0 >> auxint, shift amount 0-63
{name: "SARLconst", argLength: 1, reg: gp11, asm: "SARL", aux: "Int8", resultInArg0: true, clobberFlags: true}, // signed arg0 >> auxint, shift amount 0-31
{name: "SARWconst", argLength: 1, reg: gp11, asm: "SARW", aux: "Int8", resultInArg0: true, clobberFlags: true}, // signed arg0 >> auxint, shift amount 0-15
{name: "SARBconst", argLength: 1, reg: gp11, asm: "SARB", aux: "Int8", resultInArg0: true, clobberFlags: true}, // signed arg0 >> auxint, shift amount 0-7
{name: "SARLconst", argLength: 1, reg: gp11, asm: "SARL", aux: "Int8", resultInArg0: true, clobberFlags: true}, // signed int32(arg0) >> auxint, shift amount 0-31
{name: "SARWconst", argLength: 1, reg: gp11, asm: "SARW", aux: "Int8", resultInArg0: true, clobberFlags: true}, // signed int16(arg0) >> auxint, shift amount 0-15
{name: "SARBconst", argLength: 1, reg: gp11, asm: "SARB", aux: "Int8", resultInArg0: true, clobberFlags: true}, // signed int8(arg0) >> auxint, shift amount 0-7

{name: "ROLQ", argLength: 2, reg: gp21shift, asm: "ROLQ", resultInArg0: true, clobberFlags: true}, // arg0 rotate left arg1 bits.
{name: "ROLL", argLength: 2, reg: gp21shift, asm: "ROLL", resultInArg0: true, clobberFlags: true}, // arg0 rotate left arg1 bits.
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12 changes: 6 additions & 6 deletions src/cmd/compile/internal/ssa/rewriteAMD64.go
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34 changes: 34 additions & 0 deletions test/fixedbugs/issue23812.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
// 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.

package main

import "fmt"

func main() {
want := int32(0x3edae8)
got := foo(1)
if want != got {
panic(fmt.Sprintf("want %x, got %x", want, got))
}
}

func foo(a int32) int32 {
return shr1(int32(shr2(int64(0x14ff6e2207db5d1f), int(a))), 4)
}

func shr1(n int32, m int) int32 { return n >> uint(m) }

func shr2(n int64, m int) int64 {
if m < 0 {
m = -m
}
if m >= 64 {
return n
}

return n >> uint(m)
}

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