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cmd/compile: unnecessary bounds check when indexing relative to the end #51622

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dsnet opened this issue Mar 11, 2022 · 2 comments
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cmd/compile: unnecessary bounds check when indexing relative to the end #51622

dsnet opened this issue Mar 11, 2022 · 2 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Performance
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@dsnet
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dsnet commented Mar 11, 2022 •
edited

Using go1.17.5

Consider the following:

len(b) >= 3 && b[len(b)-3] == '#'

Part of the assembly includes:

0x002f 00047 (main.go:6)	CALL	runtime.panicIndex(SB)

This should be unnecessary since the previous len(b) >= 3 check ensures that the buffer must contain the len(b)-3 element. Thus, there is no possibility of the index panicking.

\cc @martisch @randall77
@heschi heschi added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Mar 14, 2022
@heschi heschi added this to the Backlog milestone Mar 14, 2022
@gopherbot
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Change https://go.dev/cl/406175 mentions this issue: cmd/compile: derive relation between x+delta and x in prove

@gopherbot
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Change https://go.dev/cl/402815 mentions this issue: cmd/compile: Rules to prove for better bound check elimination

@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jul 13, 2022
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