From a4b95cd092aa10b40c6be82a3e0bf1052e27122d Mon Sep 17 00:00:00 2001 From: Keith Randall Date: Thu, 8 Oct 2020 11:18:02 -0700 Subject: [PATCH] cmd/compile: fix incorrect comparison folding We lost a sign extension that was necessary. The nonnegative comparison didn't have the correct extension on it. If the larger constant is positive, but its shorter sign extension is negative, the rule breaks. Fixes #41872 Change-Id: I6592ef103f840fbb786bf8cb94fd8804c760c976 Reviewed-on: https://go-review.googlesource.com/c/go/+/260701 Trust: Keith Randall Run-TryBot: Keith Randall TryBot-Result: Go Bot Reviewed-by: Alberto Donizetti --- src/cmd/compile/internal/ssa/gen/AMD64.rules | 4 +-- src/cmd/compile/internal/ssa/rewriteAMD64.go | 8 +++--- test/fixedbugs/issue41872.go | 26 ++++++++++++++++++++ 3 files changed, 32 insertions(+), 6 deletions(-) create mode 100644 test/fixedbugs/issue41872.go diff --git a/src/cmd/compile/internal/ssa/gen/AMD64.rules b/src/cmd/compile/internal/ssa/gen/AMD64.rules index 408678f054..8a253035e0 100644 --- a/src/cmd/compile/internal/ssa/gen/AMD64.rules +++ b/src/cmd/compile/internal/ssa/gen/AMD64.rules @@ -1274,8 +1274,8 @@ (CMPQconst (ANDQconst _ [m]) [n]) && 0 <= m && m < n => (FlagLT_ULT) (CMPQconst (ANDLconst _ [m]) [n]) && 0 <= m && m < n => (FlagLT_ULT) (CMPLconst (ANDLconst _ [m]) [n]) && 0 <= m && m < n => (FlagLT_ULT) -(CMPWconst (ANDLconst _ [m]) [n]) && 0 <= m && int16(m) < n => (FlagLT_ULT) -(CMPBconst (ANDLconst _ [m]) [n]) && 0 <= m && int8(m) < n => (FlagLT_ULT) +(CMPWconst (ANDLconst _ [m]) [n]) && 0 <= int16(m) && int16(m) < n => (FlagLT_ULT) +(CMPBconst (ANDLconst _ [m]) [n]) && 0 <= int8(m) && int8(m) < n => (FlagLT_ULT) // TESTQ c c sets flags like CMPQ c 0. (TESTQconst [c] (MOVQconst [d])) && int64(c) == d && c == 0 => (FlagEQ) diff --git a/src/cmd/compile/internal/ssa/rewriteAMD64.go b/src/cmd/compile/internal/ssa/rewriteAMD64.go index 3d7eb8c9a4..32ef26f98d 100644 --- a/src/cmd/compile/internal/ssa/rewriteAMD64.go +++ b/src/cmd/compile/internal/ssa/rewriteAMD64.go @@ -6886,7 +6886,7 @@ func rewriteValueAMD64_OpAMD64CMPBconst(v *Value) bool { return true } // match: (CMPBconst (ANDLconst _ [m]) [n]) - // cond: 0 <= m && int8(m) < n + // cond: 0 <= int8(m) && int8(m) < n // result: (FlagLT_ULT) for { n := auxIntToInt8(v.AuxInt) @@ -6894,7 +6894,7 @@ func rewriteValueAMD64_OpAMD64CMPBconst(v *Value) bool { break } m := auxIntToInt32(v_0.AuxInt) - if !(0 <= m && int8(m) < n) { + if !(0 <= int8(m) && int8(m) < n) { break } v.reset(OpAMD64FlagLT_ULT) @@ -8243,7 +8243,7 @@ func rewriteValueAMD64_OpAMD64CMPWconst(v *Value) bool { return true } // match: (CMPWconst (ANDLconst _ [m]) [n]) - // cond: 0 <= m && int16(m) < n + // cond: 0 <= int16(m) && int16(m) < n // result: (FlagLT_ULT) for { n := auxIntToInt16(v.AuxInt) @@ -8251,7 +8251,7 @@ func rewriteValueAMD64_OpAMD64CMPWconst(v *Value) bool { break } m := auxIntToInt32(v_0.AuxInt) - if !(0 <= m && int16(m) < n) { + if !(0 <= int16(m) && int16(m) < n) { break } v.reset(OpAMD64FlagLT_ULT) diff --git a/test/fixedbugs/issue41872.go b/test/fixedbugs/issue41872.go new file mode 100644 index 0000000000..837d61ae0a --- /dev/null +++ b/test/fixedbugs/issue41872.go @@ -0,0 +1,26 @@ +// run + +// 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. + +package main + +//go:noinline +func f8(x int32) bool { + return byte(x&0xc0) == 64 +} + +//go:noinline +func f16(x int32) bool { + return uint16(x&0x8040) == 64 +} + +func main() { + if !f8(64) { + panic("wanted true, got false") + } + if !f16(64) { + panic("wanted true, got false") + } +} -- 2.50.0