On Sun, Mar 22, 2020 at 6:34 AM Aaron Ballman <aa...@aaronballman.com> wrote:
> On Sat, Mar 21, 2020 at 11:31 PM David Blaikie <dblai...@gmail.com> wrote: > > > > Why the change? this seems counter to LLVM's style which pretty > consistently uses unreachable rather than assert(false), so far as I know? > > We're not super consistent (at least within Clang), but the rules as > I've generally understood them are to use llvm_unreachable only for > truly unreachable code and to use assert(false) when the code is > technically reachable but is a programmer mistake to have gotten > there. I don't see those as two different things personally - llvm_unreachable is used when the programmer believes it to be unreachable (not that it must be proven to be unreachable - we have message text there so it's informative if the assumption turns out not to hold) > In this particular case, the code is very much reachable In what sense? If it is actually reachable - shouldn't it be tested? (& in which case the assert(false) will get in the way of that testing) > and I > spent a lot more time debugging than I should have because I was using > a release + asserts build and the semantics of llvm_unreachable made > unfortunate codegen (switching to an assert makes the issue > immediately obvious). > I think it might be reasonable to say that release+asserts to have unreachable behave the same way unreachable behaves at -O0 (which is to say, much like assert(false)). Clearly release+asserts effects code generation, so there's nothing like the "debug info invariance" goal that this would be tainting, etc. Certainly opinions vary here, but here are some commits that show the sort of general preference: http://llvm.org/viewvc/llvm-project?view=revision&revision=259302 http://llvm.org/viewvc/llvm-project?view=revision&revision=253005 http://llvm.org/viewvc/llvm-project?view=revision&revision=251266 And some counter examples: http://llvm.org/viewvc/llvm-project?view=revision&revision=225043 Including this thread where Chandler originally (not sure what his take on it is these days) expressed some ideas more along your lines: http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20110919/thread.html#46583 But I'm always pretty concerned about the idea that assertions should be used in places where the behavior of the program has any constraints when the assertion is false... - Dave > > > > > On Tue, Mar 10, 2020 at 11:22 AM Aaron Ballman via cfe-commits < > cfe-commits@lists.llvm.org> wrote: > >> > >> > >> Author: Aaron Ballman > >> Date: 2020-03-10T14:22:21-04:00 > >> New Revision: 4a0267e3ad8c4d47f267d7d960f127e099fb4818 > >> > >> URL: > https://github.com/llvm/llvm-project/commit/4a0267e3ad8c4d47f267d7d960f127e099fb4818 > >> DIFF: > https://github.com/llvm/llvm-project/commit/4a0267e3ad8c4d47f267d7d960f127e099fb4818.diff > >> > >> LOG: Convert a reachable llvm_unreachable into an assert. > >> > >> Added: > >> > >> > >> Modified: > >> clang/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp > >> > >> Removed: > >> > >> > >> > >> > ################################################################################ > >> diff --git a/clang/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp > b/clang/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp > >> index 01ac2bc83bb6..99e16752b51a 100644 > >> --- a/clang/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp > >> +++ b/clang/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp > >> @@ -134,9 +134,9 @@ StringRef > AnalyzerOptions::getCheckerStringOption(StringRef CheckerName, > >> CheckerName = CheckerName.substr(0, Pos); > >> } while (!CheckerName.empty() && SearchInParents); > >> > >> - llvm_unreachable("Unknown checker option! Did you call > getChecker*Option " > >> - "with incorrect parameters? User input must've been > " > >> - "verified by CheckerRegistry."); > >> + assert(false && "Unknown checker option! Did you call > getChecker*Option " > >> + "with incorrect parameters? User input must've been " > >> + "verified by CheckerRegistry."); > >> > >> return ""; > >> } > >> > >> > >> > >> _______________________________________________ > >> cfe-commits mailing list > >> cfe-commits@lists.llvm.org > >> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >
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