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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>
24 lines
417 B
Go
24 lines
417 B
Go
// run
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// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Issue 29402: wrong optimization of comparison of
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// constant and shift on MIPS.
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package main
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//go:noinline
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func F(s []int) bool {
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half := len(s) / 2
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return half >= 0
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}
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func main() {
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b := F([]int{1, 2, 3, 4})
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if !b {
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panic("FAIL")
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}
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}
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