Unable to create large (500 elements) unordered maps due to compilation errors VS2017

[shivendra14]

I am just trying to compile following code, without success. With smaller number of pairs there is just a warning, no error.

#define k500Pairs {0,0},{1,1},{2,2},{3,3},{4,4},{5,5},{6,6},{7,7},{8,8},{9,9},{10,10},{11,11},{12,12},{13,13},{14,14},{15,15},{16,16},{17,17},{18,18},{19,19},{20,20},{21,21},{22,22},{23,23},{24,24},{25,25},{26,26},{27,27},{28,28},{29,29},{30,30},{31,31},{32,32},{33,33},{34,34},{35,35},{36,36},{37,37},{38,38},{39,39},{40,40},{41,41},{42,42},{43,43},{44,44},{45,45},{46,46},{47,47},{48,48},{49,49},{50,50},{51,51},{52,52},{53,53},{54,54},{55,55},{56,56},{57,57},{58,58},{59,59},{60,60},{61,61},{62,62},{63,63},{64,64},{65,65},{66,66},{67,67},{68,68},{69,69},{70,70},{71,71},{72,72},{73,73},{74,74},{75,75},{76,76},{77,77},{78,78},{79,79},{80,80},{81,81},{82,82},{83,83},{84,84},{85,85},{86,86},{87,87},{88,88},{89,89},{90,90},{91,91},{92,92},{93,93},{94,94},{95,95},{96,96},{97,97},{98,98},{99,99},{100,100},{101,101},{102,102},{103,103},{104,104},{105,105},{106,106},{107,107},{108,108},{109,109},{110,110},{111,111},{112,112},{113,113},{114,114},{115,115},{116,116},{117,117},{118,118},{119,119},{120,120},{121,121},{122,122},{123,123},{124,124},{125,125},{126,126},{127,127},{128,128},{129,129},{130,130},{131,131},{132,132},{133,133},{134,134},{135,135},{136,136},{137,137},{138,138},{139,139},{140,140},{141,141},{142,142},{143,143},{144,144},{145,145},{146,146},{147,147},{148,148},{149,149},{150,150},{151,151},{152,152},{153,153},{154,154},{155,155},{156,156},{157,157},{158,158},{159,159},{160,160},{161,161},{162,162},{163,163},{164,164},{165,165},{166,166},{167,167},{168,168},{169,169},{170,170},{171,171},{172,172},{173,173},{174,174},{175,175},{176,176},{177,177},{178,178},{179,179},{180,180},{181,181},{182,182},{183,183},{184,184},{185,185},{186,186},{187,187},{188,188},{189,189},{190,190},{191,191},{192,192},{193,193},{194,194},{195,195},{196,196},{197,197},{198,198},{199,199},{200,200},{201,201},{202,202},{203,203},{204,204},{205,205},{206,206},{207,207},{208,208},{209,209},{210,210},{211,211},{212,212},{213,213},{214,214},{215,215},{216,216},{217,217},{218,218},{219,219},{220,220},{221,221},{222,222},{223,223},{224,224},{225,225},{226,226},{227,227},{228,228},{229,229},{230,230},{231,231},{232,232},{233,233},{234,234},{235,235},{236,236},{237,237},{238,238},{239,239},{240,240},{241,241},{242,242},{243,243},{244,244},{245,245},{246,246},{247,247},{248,248},{249,249},{250,250},{251,251},{252,252},{253,253},{254,254},{255,255},{256,256},{257,257},{258,258},{259,259},{260,260},{261,261},{262,262},{263,263},{264,264},{265,265},{266,266},{267,267},{268,268},{269,269},{270,270},{271,271},{272,272},{273,273},{274,274},{275,275},{276,276},{277,277},{278,278},{279,279},{280,280},{281,281},{282,282},{283,283},{284,284},{285,285},{286,286},{287,287},{288,288},{289,289},{290,290},{291,291},{292,292},{293,293},{294,294},{295,295},{296,296},{297,297},{298,298},{299,299},{300,300},{301,301},{302,302},{303,303},{304,304},{305,305},{306,306},{307,307},{308,308},{309,309},{310,310},{311,311},{312,312},{313,313},{314,314},{315,315},{316,316},{317,317},{318,318},{319,319},{320,320},{321,321},{322,322},{323,323},{324,324},{325,325},{326,326},{327,327},{328,328},{329,329},{330,330},{331,331},{332,332},{333,333},{334,334},{335,335},{336,336},{337,337},{338,338},{339,339},{340,340},{341,341},{342,342},{343,343},{344,344},{345,345},{346,346},{347,347},{348,348},{349,349},{350,350},{351,351},{352,352},{353,353},{354,354},{355,355},{356,356},{357,357},{358,358},{359,359},{360,360},{361,361},{362,362},{363,363},{364,364},{365,365},{366,366},{367,367},{368,368},{369,369},{370,370},{371,371},{372,372},{373,373},{374,374},{375,375},{376,376},{377,377},{378,378},{379,379},{380,380},{381,381},{382,382},{383,383},{384,384},{385,385},{386,386},{387,387},{388,388},{389,389},{390,390},{391,391},{392,392},{393,393},{394,394},{395,395},{396,396},{397,397},{398,398},{399,399},{400,400},{401,401},{402,402},{403,403},{404,404},{405,405},{406,406},{407,407},{408,408},{409,409},{410,410},{411,411},{412,412},{413,413},{414,414},{415,415},{416,416},{417,417},{418,418},{419,419},{420,420},{421,421},{422,422},{423,423},{424,424},{425,425},{426,426},{427,427},{428,428},{429,429},{430,430},{431,431},{432,432},{433,433},{434,434},{435,435},{436,436},{437,437},{438,438},{439,439},{440,440},{441,441},{442,442},{443,443},{444,444},{445,445},{446,446},{447,447},{448,448},{449,449},{450,450},{451,451},{452,452},{453,453},{454,454},{455,455},{456,456},{457,457},{458,458},{459,459},{460,460},{461,461},{462,462},{463,463},{464,464},{465,465},{466,466},{467,467},{468,468},{469,469},{470,470},{471,471},{472,472},{473,473},{474,474},{475,475},{476,476},{477,477},{478,478},{479,479},{480,480},{481,481},{482,482},{483,483},{484,484},{485,485},{486,486},{487,487},{488,488},{489,489},{490,490},{491,491},{492,492},{493,493},{494,494},{495,495},{496,496},{497,497},{498,498},{499,499}

#define kN 500

constexpr frozen::unordered_map<int, int, kN> fum{kPairs};

Build FAILED.

"C:\Perforce\fixed_container\build\ALL_BUILD.vcxproj" (default target) (1) ->
"C:\Perforce\fixed_container\build\app\FixedContainer.vcxproj" (default target)
(3) ->
(ClCompile target) ->
c:\perforce\fixed_container\app\main.cpp(20): warning C4307: '+': integral con
stant overflow [C:\Perforce\fixed_container\build\app\FixedContainer.vcxproj]

"C:\Perforce\fixed_container\build\ALL_BUILD.vcxproj" (default target) (1) ->
"C:\Perforce\fixed_container\build\app\FixedContainer.vcxproj" (default target)
(3) ->
(ClCompile target) ->
c:\perforce\fixed_container\app\main.cpp(20): error C2131: expression did not
evaluate to a constant [C:\Perforce\fixed_container\build\app\FixedContainer.vcx
proj]

1 Warning(s)
1 Error(s)

[shivendra14]

Any clue why this is not evaluating to constant expression
constexpr frozen::unordered_map<int, int, kN> fum{kPairs};

https://github.com/shivendra14/fixed_container/blob/7a8209a2b0cd191e49a55fad60824a7687fd3402/app/main.cpp#L20

[degski]

@shivendra14 It's not a constant expression because of the integer overflow:

c:\perforce\fixed_container\app\main.cpp(20): warning C4307: '+': integral con
stant overflow [C:\Perforce\fixed_container\build\app\FixedContainer.vcxproj]

any error will produce: "is not a constant expression", which basically means (in this case), there is no expression at all.

[shivendra14]

@degski: okay.. any clue, where am I exceeding integral limit, and how to fix that?

[degski]

It's possible that some iteration exceeds some arbitrary limit [or a recursion some depth]. I know how to fix that in Clang, but not in VC.

These things are rather hard to debug, because you're attempting to debug the compilation process, which is not designed to be debugged, in general.

[shivendra14]

Well I have my code opensourced at: https://github.com/shivendra14/fixed_container/blob/7a8209a2b0cd191e49a55fad60824a7687fd3402/app/main.cpp#L20

Its quite disappointing bug, since I am not able to use unordered _map at all provided in this library.

[degski]

@shivendra14 Looking at the help-screens (> cl.exe /?), there are these compiler flags you should/could try (VS2019, I don't have VS2017 installed, so I don't know about that, and cannot check it):

/constexpr:depth<N>     recursion depth limit for constexpr evaluation (default: 512)
/constexpr:backtrace<N> show N constexpr evaluations in diagnostics (default: 10)
/constexpr:steps<N>     terminate constexpr evaluation after N steps (default: 100000)

[shivendra14]

ok. But there is more to this bug. Its not just about large number of elements. This attempt to make constexpr unordered_map causes warning even for just a single entry.

Also, I tried making it a static const instead of a constexpr, but my applications hangs with this.. Something is really wierd going on in unorderd_map
static const frozen::unordered_map<int, int, kN+1> fum {{10,2}, kPairs};