[llvm] 4e6d372 - [LiveDebugValues] Use std::sort for register sorting in collectIDsForRegs (#194339)

[via llvm-commits]

Author: Cullen Rhodes
Date: 2026-04-27T14:53:03+01:00
New Revision: 4e6d3722fca73c97367720180a8d547057fda380

URL: https://github.com/llvm/llvm-project/commit/4e6d3722fca73c97367720180a8d547057fda380
DIFF: https://github.com/llvm/llvm-project/commit/4e6d3722fca73c97367720180a8d547057fda380.diff

LOG: [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

Added: 
    

Modified: 
    llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp b/llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp
index 293dfa53c3c84..22db660f78f9f 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp
@@ -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) {