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cmd/compile: bad walkinrange rewrites on constant above 2**63 [1.11 backport] #27246

gopherbot opened this issue Aug 26, 2018 · 3 comments


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@gopherbot gopherbot commented Aug 26, 2018

@josharian requested issue #27143 to be considered for backport to the next 1.11 minor release.

Certainly seems to qualify for a backport.

Yeah. My hesitation was only that this appears to have existed for many releases, and the symptom is a spurious compiler error (not bad code generation). Nevertheless, I agree.

@gopherbot please open backport tracking issues.


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@gopherbot gopherbot commented Aug 27, 2018

Change mentions this issue: [release-branch.go1.11] cmd/compile: prevent overflow in walkinrange


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@randall77 randall77 commented Sep 11, 2018

@andybons : CL is ready to be submitted.


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@gopherbot gopherbot commented Sep 13, 2018

Closed by merging c9ca36f to release-branch.go1.11.

@gopherbot gopherbot closed this Sep 13, 2018
gopherbot pushed a commit that referenced this issue Sep 13, 2018
In the compiler frontend, walkinrange indiscriminately calls Int64()
on const CTINT nodes, even though Int64's return value is undefined
for anything over 2⁶³ (in practise, it'll return a negative number).

This causes the introduction of bad constants during rewrites of
unsigned expressions, which make the compiler reject valid Go

This change introduces a preliminary check that Int64() is safe to
call on the consts on hand. If it isn't, walkinrange exits without
doing any rewrite.

Fixes #27246

Change-Id: I2017073cae65468a521ff3262d4ea8ab0d7098d9
Run-TryBot: Josh Bleecher Snyder <>
TryBot-Result: Gobot Gobot <>
Reviewed-by: Josh Bleecher Snyder <>
(cherry picked from commit 42cc4ca)
Reviewed-by: Robert Griesemer <>
Run-TryBot: Andrew Bonventre <>
@golang golang locked and limited conversation to collaborators Sep 13, 2019
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