[lld/mac] Replace while loop with for loop

[thakis]

Summary

No behavior change. In preparation for using a parallelFor() here.

[tschuett]

Nit. Your are not allowed to check getBlockCount() for every iteration. Pull it out of the loop?

[thakis]

Hm?

[tschuett]

https://llvm.org/docs/CodingStandards.html#don-t-evaluate-end-every-time-through-a-loop

Or does getBlockCount()changes in every iteration?

[thakis]

In D128295#3599940, @tschuett wrote:

Nit. Your are not allowed to check getBlockCount() for every iteration. Pull it out of the loop?

I don't understand what this means. Do you mean i < getBlockCount() in the loop conditional? Pretty sure all compilers strength-reduce this (e.g. https://godbolt.org/z/qjMW6cErh)

[thakis]

(in any case, it's irrelevant after D128298)

[tschuett]

LGTM

[thakis]

Thanks! :)

lld/MachO/SyntheticSections.cpp

 
 uint64_t CodeSignatureSection::getRawSize() const {
   return allHeadersSize + getBlockCount() * hashSize;
 }
 
 void CodeSignatureSection::writeHashes(uint8_t *buf) const {
   // NOTE: Changes to this functionality should be repeated in llvm-objcopy's
   // MachOWriter::writeSignatureData.
-  uint8_t *code = buf;
-  uint8_t *codeEnd = buf + fileOff;
-  uint8_t *hashes = codeEnd + allHeadersSize;
-  while (code < codeEnd) {
-    sha256(code, std::min(static_cast<size_t>(codeEnd - code), blockSize),
-           hashes);
-    code += blockSize;
-    hashes += hashSize;
+  uint8_t *hashes = buf + fileOff + allHeadersSize;
+  for (uint64_t i = 0; i < getBlockCount(); ++i) {
+    sha256(buf + i * blockSize,
+           std::min(static_cast<size_t>(fileOff - i * blockSize), blockSize),
+           hashes + i * hashSize);
   }
 #if defined(__APPLE__)
   // This is macOS-specific work-around and makes no sense for any
   // other host OS. See https://openradar.appspot.com/FB8914231
   //
   // The macOS kernel maintains a signature-verification cache to
   // quickly validate applications at time of execve(2).  The trouble
   // is that for the kernel creates the cache entry at the time of the