[Coverage] getMaxBitmapSize: Scan max(BitmapIdx) instead of the last Decision

[chapuni]

In CoverageMapping.cpp:getMaxBitmapSize(),
this assumed that the last Decision has the maxmum BitmapIdx.

Let it scan max(BitmapIdx).

Note that <= is used insted of <, because BitmapIdx == 0 is valid
and MaxbitmapID is unsigned. BitmapIdx is unique in the record.

Fixes #78922

[chapuni]

Let me push the testcase in advance of the fix, to confirm failure.

[chapuni]

The record of this testcase is:

sub:
  Decision,File 0, 5:11 -> 5:59 = M:1, C:4
  Branch,File 0, 5:12 -> 5:20 = #5, ((#0 - #1) - #5) [1,3,2]
  Branch,File 0, 5:24 -> 5:32 = #6, (#5 - #6) [3,0,2]
  Branch,File 0, 5:38 -> 5:46 = #7, (#4 - #7) [2,4,0]
  Branch,File 0, 5:50 -> 5:58 = #8, (#7 - #8) [4,0,0]
  Decision,File 1, 1:23 -> 1:47 = M:0, C:2
  Branch,File 1, 1:23 -> 1:33 = #2, (#0 - #2) [1,2,0]
  Branch,File 1, 1:37 -> 1:47 = #3, (#2 - #3) [2,0,0]

The current implementation picks up M:0 C:2.

[chapuni]

llvm/lib/ProfileData/Coverage/CoverageMapping.cpp:232: Expected<BitVector> llvm::coverage::CounterMappingContext::evaluateBitmap(const CounterMappingRegion *) const: Assertion `ID + SizeInBytes <= BitmapBytes.size() && "BitmapBytes overrun"' failed. in https://buildkite.com/llvm-project/github-pull-requests/builds/31563

[ornata]

LGTM

[chapuni]

https://lab.llvm.org/buildbot/#/builders/16/builds/60018

error: failed to load coverage: 'llvm/test/tools/llvm-cov/Inputs/mcdc-maxbs.o': profile uses zlib compression but the profile reader was built without zlib support

I'll rework.

[ornata]

Will the new test fail when the profile reader is built with zlib support? :(

[chapuni]

Should be fixed in d386c40

@ornata It was failing on zlib-unsupported hosts since I enabled zlib locally.