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cmd/compile: MOVWreg missing sign-extension following a Copy from a floating-point LoadReg [1.16 backport] #50682

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gopherbot opened this issue Jan 19, 2022 · 3 comments
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cmd/compile: MOVWreg missing sign-extension following a Copy from a floating-point LoadReg [1.16 backport] #50682

gopherbot opened this issue Jan 19, 2022 · 3 comments
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CherryPickApproved Used during the release process for point releases FrozenDueToAge
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Go1.16.14

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@gopherbot
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@bcmills requested issue #50671 to be considered for backport to the next 1.16 minor release.

@gopherbot, please backport to Go 1.16 and Go 1.17. This is a compiler bug that causes subtle run-time data corruption; it is hard to predict which code might be affected, and the corrupted paths might not be triggered by tests, but it appears to cause a nonzero rate of failures in the Go builders. The fix is small and MIPS-specific, so backporting it seems low-risk.
@gopherbot gopherbot added the CherryPickCandidate Used during the release process for point releases label Jan 19, 2022
@gopherbot gopherbot mentioned this issue Jan 19, 2022
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@gopherbot gopherbot added this to the Go1.16.14 milestone Jan 19, 2022
@toothrot toothrot added the CherryPickApproved Used during the release process for point releases label Jan 19, 2022
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This generates the wrong code and the fix is low risk. Approved.

@gopherbot gopherbot removed the CherryPickCandidate Used during the release process for point releases label Jan 19, 2022
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Change https://golang.org/cl/379515 mentions this issue: [release-branch.go1.16] cmd/compile: don't elide extension for LoadReg to FP register on MIPS64

@gopherbot
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Closed by merging fcd482a to release-branch.go1.16.

gopherbot pushed a commit that referenced this issue Feb 7, 2022
@cherrymui
[release-branch.go1.16] cmd/compile: don't elide extension for LoadRe…
fcd482a 
…g to FP register on MIPS64

For an extension operation like MOVWreg, if the operand is already
extended, we optimize the second extension out. Usually a LoadReg
of a proper type would come already extended, as a MOVW/MOVWU etc.
instruction does. But for a LoadReg to a floating point register,
the instruction does not do the extension. So we cannot elide the
extension.

Updates #50671.
Fixes #50682.

Change-Id: Id8991df78d5acdecd3fd6138c558428cbd5f6ba3
Reviewed-on: https://go-review.googlesource.com/c/go/+/379236
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
(cherry picked from commit d93ff73)
Reviewed-on: https://go-review.googlesource.com/c/go/+/379515
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