Visual C++ optimeerija lahendab Visual Studio 2015 Update 3

Lahendus

Selle kiirparanduse lahendatavad probleemid

See kiirparandus sisaldab lahendab järgmised probleemid:

• Parandab vea optimeerija kui tõstmiseks tsükkel-variant tingimuslik poe väljaspool tsükkel: #include <cstdlib> #include <cassert> struct Foo { int a; int b; }; int main() { Foo foo; foo.b = rand(); int a = rand(); int b = foo.b; for (int i = 0; i < 10; ++i) { int inner_b = b; int inner_a = a; if (inner_b < 0) // This gets incorrect hoisted outside the loop. // A workaround is /d2SSAOptimizer- { inner_a = 0; inner_b = 0; } if (inner_b >= 0) assert(inner_a == a); a += b; } return 0; }

   

• Täisarv division viga, optimeerija PARANDUS: #include <stdio.h> volatile int z = 0; int main() { unsigned a, b; __int64 c; a = z; c = a; c = (c == 0) ? 1LL : c; b = (unsigned)((__int64)a * 100 / c); // Division was made unconditional // incorrectly creating a divide by zero. // A workaround is /d2SSAOptimizer- printf("%u\n", b); return 0; }

   

• Täisarv division viga, optimeerija PARANDUS: int checkchecksum(int suly, int ell, int utkodert) { int x; ell -= utkodert; ell %= 103; if (suly - 1) utkodert /= (suly - 1); // Division was made unconditional, // incorrectly creating a potential divide by zero // A workaround is /d2SSAOptimizer- return utkodert; }

   

• Täisarv division viga, optimeerija PARANDUS: typedef int unsigned uint; volatile uint out_index = 0; bool data[1] = {true}; bool __declspec(noinline) BugSSA(uint index) { uint group = index / 3; if (group == 0) // The division result being compared to zero is replaced // with a range check. We then incorrectly move the division { // to the next use of "group", without accounting for the fact // that "index" has changed. A workaround is /d2SSAOptimizer- return false; } index -= 3; group--; bool ret = data[group]; // crash here out_index = index; out_index = index; return ret; } int main() { volatile uint i = 3; return BugSSA(i); }

   

• Lahenda crash optimeerija MIN_INT division, – 1: int test_div(bool flag, int dummy) { int result = std::numeric_limits<int>::min(); int other; if (flag) other = -1; else other = dummy - 1 - dummy; result /= other; // We would push the division up into both arms of the // if-then-else. One of those divisions would cause the // optimizer to evaluate MIN_INT/-1.This is a crash, similar // to dividing by zero. A workaround is /d2SSAOptimizer- return result; }

   

• Lahendab pinu ülevool optimeerija. #include <stdio.h> // This example produced a stack overflow in the optimizer, which was // caused by mutually-recursive analysis functions not properly tracking // the number of times they were invocated. // A workaround is /d2SSAOptimizer- typedef unsigned char byte; typedef unsigned long long int uint64; int main() { const uint64 *sieveData = new uint64[1024]; uint64 bitIndexShift = 0; uint64 curSieveChunk = 0xfafd7bbef7ffffffULL & ~uint64(3); const unsigned int *NumbersCoprimeToModulo = new unsigned int[16]; const unsigned int *PossiblePrimesForModuloPtr = NumbersCoprimeToModulo; while (!curSieveChunk) { curSieveChunk = *(sieveData++); const uint64 NewValues = (16 << 8) | (32 << 24); bitIndexShift = (NewValues >> (bitIndexShift + 8)) & 255; PossiblePrimesForModuloPtr = NumbersCoprimeToModulo + bitIndexShift; } if (PossiblePrimesForModuloPtr - NumbersCoprimeToModulo != 0) { printf("fail"); return 1; } printf("pass"); return 0; }

   

• Parandada vale koodi loomine, kui eemaldage liigne ujuv punkti teisendused seotud teisendada f64 int32 parameeter: #include <string> __declspec(noinline) void test(int Val) { double Val2 = Val; std::string Str; printf("%lld\n", __int64(Val2)); // We incorrectly try to read 64 bits of // floating point from the parameter area, // instead of reading 32 bits of integer // and converting it. A workaround is // to throw /d2SSAOptimizer- } int main() { test(6); test(7); return 0; }

   

• Parandab krahhi optimeerija kui osadeks vool graph sõlmede vaikimisi lause lüliti ploki täpsema teabe saamiseks vt https://bugs.chromium.org/p/chromium/issues/detail?id=627216#c15.

• Parandab vea silmus optimeerija kui me täita allkirjastamata teisene esilekutsumiseks muutujaid liiki esmane esilekutsumiseks muutuja vale tugevus vähendamine: #include <assert.h> #include <malloc.h> #include <stdio.h> typedef unsigned int uint; typedef unsigned char byte; /* There is a corner case in the compiler's loop optimizer. The corner case arose if an induction variable (IV) is a multiple of the loop index, and there's a comparison of the IV to an integer that is less than this multiplication factor. A workaround is to use #pragma optimize("", off) / #pragma optimize("", on) around the affected function. */ int main(int argc, char *argv[]) { const uint w = 256; const uint h = 64; const uint w_new = w >> 1; const uint h_new = h >> 1; const byte *const src = (byte *)malloc(w * h); byte *it_out = (byte *)malloc(w_new * h_new); int fail = 0; for (uint y_new = 0; y_new < h_new; ++y_new) { for (uint x_new = 0; x_new < w_new; ++x_new, ++it_out) { uint x = x_new * 2; uint y = y_new * 2; if (x < 1 || y < 1) { *it_out = 0; continue; } if (x != 0) { } else { fail = 1; } *it_out = 4 * src[y * w + x]; } } if (fail) { printf("fail\n"); return (1); } printf("pass\n"); return (0); }

   

• Pakub sellele probleemile lahendust C4883 ": funktsiooni maht takistab optimeerimine". Kui see optimeerija näeb funktsioone, mis on suur, see skaala tagasi optimeerimine, mille sooritab. See väljastab hoiatuse C4883 kui seda tehakse, kui on lubatud hoiatus /we4883 kaudu. Kui soovite tühistada selle otsuse maha suruda optimeerimine, viska /d2OptimizeHugeFunctions lüliti.

• Parandab C2 kompilaator crash! PpCanPropagateForward optimeerimine x64 sooritamisel.

• Parandab silmus optimeerija vead, mis hõlmavad vale esilekutsumiseks muutuv tugevust vähendada.

• Parandab vale kordustellimise avaldised, mis hõlmavad loeb ja kirjutab mälu tõttu vale alias kontrollimine.

• Parandab registri jaoturi viga, mis hõlmab a kompilaator genereeritud ajutise olemasoleva üle mitme erandite käsitsemise piirkonnad.

Olek

Microsoft on kinnitanud, et see probleem esineb jaotises "Kehtib järgmiste toodete kohta" loetletud Microsofti toodetel.