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x/tools/go/ssa: misrepresents the dynamic behavior of shift with signed rhs #51363

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dominikh opened this issue Feb 25, 2022 · 2 comments
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x/tools/go/ssa: misrepresents the dynamic behavior of shift with signed rhs #51363

dominikh opened this issue Feb 25, 2022 · 2 comments
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Analysis Issues related to static analysis (vet, x/tools/go/analysis) FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. Tools This label describes issues relating to any tools in the x/tools repository.
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Unreleased

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@dominikh
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Input:

package main

func foo(x int) { _ = 1 << x }
func main()     { foo(-1) }

Output:

func foo(x int):
0:                                                                entry P:0 S:0
	t0 = convert uint64 <- int (x)                                   uint64
	t1 = 1:int << t0                                                    int
	return

Actual runtime behavior:

$ go run bar.go                                                                
panic: runtime error: negative shift amount

This issue is very similar to #50949, with much of the same possible fixes.

/cc @timothy-king
@dominikh dominikh added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Tools This label describes issues relating to any tools in the x/tools repository. Analysis Issues related to static analysis (vet, x/tools/go/analysis) labels Feb 25, 2022
@gopherbot gopherbot added this to the Unreleased milestone Feb 25, 2022
@timothy-king
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Thanks. Confirmed this is a bug.

The relevant code is here: https://cs.opensource.google/go/x/tools/+/refs/tags/v0.1.9:go/ssa/emit.go;l=76-80

@timothy-king timothy-king added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Feb 25, 2022
@gopherbot
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Change https://go.dev/cl/387995 mentions this issue: go/ssa: allows right operand of a shift to be signed.

@golang golang locked and limited conversation to collaborators Feb 26, 2023
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Labels
Analysis Issues related to static analysis (vet, x/tools/go/analysis) FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. Tools This label describes issues relating to any tools in the x/tools repository.
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@dominikh @timothy-king @gopherbot