Unverified Commit 4e6d3722 authored by Cullen Rhodes's avatar Cullen Rhodes Committed by GitHub
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[LiveDebugValues] Use std::sort for register sorting in collectIDsForRegs (#194339) 

VarLocBasedLDV::collectIDsForRegs sorts a SmallVector<Register> using
array_pod_sort which is a thin wrapper around qsort. That shows up as a hotspot
in compile-time profiles under __GI___qsort_r.

Switching this to an explicit-comparator llvm::sort call, which takes the
std::sort path instead improves compile-time with no change to code-size.

CTMark geomean:
- stage1-O0-g: -0.41%
- stage1-aarch64-O0-g: -0.58%
- stage2-O0-g: -0.40%

http://llvm-compile-time-tracker.com/compare.php?from=347aa3f6fbcc48cd752d02aa581b74c33d18dd41&to=cca8df56a576682510733c4c1b6fc12556e2dd7c&stat=instructions%3Au
parent c6de992a

llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp

+1 −1
Original line number Diff line number Diff line
@@ -1208,7 +1208,7 @@ void VarLocBasedLDV::collectIDsForRegs(VarLocsInRange &Collected, 
  assert(!Regs.empty() && "Nothing to collect");

  SmallVector<Register, 32> SortedRegs;

  append_range(SortedRegs, Regs);

  array_pod_sort(SortedRegs.begin(), SortedRegs.end());

  llvm::sort(SortedRegs, [](Register LHS, Register RHS) { return LHS < RHS; });

  auto It = CollectFrom.find(LocIndex::rawIndexForReg(SortedRegs.front()));

  auto End = CollectFrom.end();

  for (Register Reg : SortedRegs) {