覆盖率数据中出现意外的分支计数

Unexpected branch count in coverage data

本文关键字：分支 意外 数据 覆盖率      更新时间：2023-10-16

我生成覆盖率数据，并使用在线服务进行可视化和CI。然而，我有奇怪的"部分"（如果分支没有完全覆盖）。从gcov数据来看，似乎检测到了过多的分支。

一个例子：

function _ZNK5World8AdjustBQE5PointItEh15BuildingQuality called 415 returned 100% blocks executed 76%
      415:  377:BuildingQuality World::AdjustBQ(const MapPoint pt, unsigned char player, BuildingQuality nodeBQ) const
        -:  378:{
      415:  379:    if(nodeBQ == BQ_NOTHING || GetNode(pt).owner != player + 1 || !IsPlayerTerritory(pt))
branch  0 taken 95% (fallthrough)
branch  1 taken 5%
call    2 returned 100%
call    3 returned 100%
branch  4 taken 100% (fallthrough)
branch  5 taken 0% (throw)
branch  6 taken 85% (fallthrough)
branch  7 taken 15%
call    8 returned 100%
call    9 returned 100%
branch 10 taken 100% (fallthrough)
branch 11 taken 0% (throw)
branch 12 taken 17% (fallthrough)
branch 13 taken 83%
branch 14 taken 80% (fallthrough)
branch 15 taken 20%
branch 16 taken 95% (fallthrough)
branch 17 taken 5%
branch 18 taken 33% (fallthrough)
branch 19 taken 67%
branch 20 never executed
branch 21 never executed
branch 22 never executed
branch 23 never executed
call   24 never executed

尽管我已经在使用-g -O0 --coverage -fno-default-inline -fno-inline进行编译，但函数似乎仍然被内联和计数。我该怎么办，这样我只得到"有意义的全部"数据，并且内联函数在其定义中被正确地归因？

我使用g++-4.8和gcov-4.8

编辑：如果我把If分成它的调用，我会得到这个：

      415:  379:    unsigned char owner = GetNode(pt).owner;
call    0 returned 100%
call    1 returned 100%
branch  2 taken 100% (fallthrough)
branch  3 taken 0% (throw)
call    4 never executed
      415:  380:    bool isPlayerTer = IsPlayerTerritory(pt);
call    0 returned 100%
call    1 returned 100%
branch  2 taken 100% (fallthrough)
branch  3 taken 0% (throw)
call    4 never executed
      415:  381:    if(nodeBQ == BQ_NOTHING || owner != player + 1 || !isPlayerTer)
branch  0 taken 95% (fallthrough)
branch  1 taken 5%
branch  2 taken 85% (fallthrough)
branch  3 taken 15%
branch  4 taken 17% (fallthrough)
branch  5 taken 83%

所以问题实际上在于电话。我该怎么做才能使这些呼叫（及其分支（？？？））不添加到覆盖范围数据中？

刚刚在asm代码中发现了一个人工分支，它只检查一个寄存器并执行nop（除了gcov计数器增量）WTF？

   0x0000000000d967de <World::AdjustBQ(Point<unsigned short>, unsigned char, BuildingQuality) const+340>:   test   %bl,%bl
   0x0000000000d967e0 <World::AdjustBQ(Point<unsigned short>, unsigned char, BuildingQuality) const+342>:   je     0xd967f5 <World::AdjustBQ(Point<unsigned short>, unsigned char, BuildingQuality) const+363>
   0x0000000000d967e2 <World::AdjustBQ(Point<unsigned short>, unsigned char, BuildingQuality) const+344>:   nop
   0x0000000000d967e3 <World::AdjustBQ(Point<unsigned short>, unsigned char, BuildingQuality) const+345>:   mov    0x1206c9e(%rip),%rax        # 0x1f9d488 <__gcov0._ZNK5World8AdjustBQE5PointItEh15BuildingQuality+72>
   0x0000000000d967ea <World::AdjustBQ(Point<unsigned short>, unsigned char, BuildingQuality) const+352>:   add    $0x1,%rax
   0x0000000000d967ee <World::AdjustBQ(Point<unsigned short>, unsigned char, BuildingQuality) const+356>:   mov    %rax,0x1206c93(%rip)        # 0x1f9d488 <__gcov0._ZNK5World8AdjustBQE5PointItEh15BuildingQuality+72>
   0x0000000000d967f5 <World::AdjustBQ(Point<unsigned short>, unsigned char, BuildingQuality) const+363>:   test   %dl,%dl

我切换到clang++和llvm-cov gcov，并得到了正确的结果（只有6个分支）。然而，我在其他地方也得到了一些假阳性。其中最令人不安的一个似乎是在一行的函数中间的"函数__cxx_global_array_tor调用"，而类似的行（仅更改整数参数）没有这个调用。因此，我目前的解决方案是在没有分支数据的情况下使用gcov-4.8，因为它完全不可靠。

可能在可能发生异常的点上有额外的分支，例如在函数调用点。

例如，我们在我们的（而不是noexcept）空虚拟析构函数中观察到一个带有gcov的分支，我们的测试无法覆盖它。

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