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cmd/compile: conversion from int/float typed constant to complex variable changed in 1.14 [1.14 backport] #38123

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gopherbot opened this issue Mar 28, 2020 · 3 comments
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cmd/compile: conversion from int/float typed constant to complex variable changed in 1.14 [1.14 backport] #38123

gopherbot opened this issue Mar 28, 2020 · 3 comments
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CherryPickApproved Used during the release process for point releases FrozenDueToAge
Milestone
Go1.14.3

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@gopherbot
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@ianlancetaylor requested issue #38117 to be considered for backport to the next 1.14 minor release.

Looks like we're going back to the 1.13 behavior. I'll let @griesemer review the CL, but:

@gopherbot Please open a backport to 1.14.

The compiler behavior changed the way it handles constant conversions. This can break existing programs with no workaround other than rewriting the program, which should not be needed.
@gopherbot gopherbot added the CherryPickCandidate Used during the release process for point releases label Mar 28, 2020
@gopherbot gopherbot mentioned this issue Mar 28, 2020
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@gopherbot gopherbot added this to the Go1.14.2 milestone Mar 28, 2020
@andybons andybons added the CherryPickApproved Used during the release process for point releases label Apr 7, 2020
@gopherbot gopherbot removed the CherryPickCandidate Used during the release process for point releases label Apr 7, 2020
@andybons
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andybons commented Apr 7, 2020

Approved as this is a regression with no workaround.

@andybons andybons modified the milestones: Go1.14.2, Go1.14.3 Apr 8, 2020
@gopherbot
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Change https://golang.org/cl/232719 mentions this issue: [release-branch.go1.14] cmd/compile: fix constant conversion involving complex types

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Closed by merging f4274e6 to release-branch.go1.14.

gopherbot pushed a commit that referenced this issue May 8, 2020
@mdempsky @dmitshur
[release-branch.go1.14] cmd/compile: fix constant conversion involvin…
f4274e6 
…g complex types

In CL 187657, I refactored constant conversion logic without realizing
that conversions between int/float and complex types are allowed for
constants (assuming the constant values are representable by the
destination type), but are never allowed for non-constant expressions.

This CL expands convertop to take an extra srcConstant parameter to
indicate whether the source expression is a constant; and if so, to
allow any numeric-to-numeric conversion. (Conversions of values that
cannot be represented in the destination type are rejected by
evconst.)

Fixes #38123.
For #38117.

Change-Id: Id7077d749a14c8fd910be38da170fa5254819f2b
Reviewed-on: https://go-review.googlesource.com/c/go/+/226197
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
(cherry picked from commit 3431428)
Reviewed-on: https://go-review.googlesource.com/c/go/+/232719
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
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