Re-land [MC] Fix quadratic behavior in addPendingLabel

This was discovered when compiling large unity/blob/jumbo files.

Differential Revision: https://reviews.llvm.org/D78775

(cherry picked from commit fd773e8a51b82775f411061117173a21b500642a)

2 files changed, 4 insertions, 7 deletions

diff --git a/llvm/include/llvm/MC/MCObjectStreamer.h b/llvm/include/llvm/MC/MCObjectStreamer.h
index 9e3f87565e2..701cdf30b47 100644
--- a/llvm/include/llvm/MC/MCObjectStreamer.h
+++ b/llvm/include/llvm/MC/MCObjectStreamer.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_MC_MCOBJECTSTREAMER_H
 #define LLVM_MC_MCOBJECTSTREAMER_H
 
+#include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCSection.h"
@@ -38,7 +39,7 @@ class MCObjectStreamer : public MCStreamer {
   bool EmitEHFrame;
   bool EmitDebugFrame;
   SmallVector<MCSymbol *, 2> PendingLabels;
-  SmallVector<MCSection*, 2> PendingLabelSections;
+  SmallSetVector<MCSection *, 4> PendingLabelSections;
   unsigned CurSubsectionIdx;
   struct PendingMCFixup {
     const MCSymbol *Sym;
diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index 3d1358df475..e05a0ec11f5 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -59,12 +59,8 @@ void MCObjectStreamer::addPendingLabel(MCSymbol* S) {
     CurSection->addPendingLabel(S, CurSubsectionIdx);
 
     // Add this Section to the list of PendingLabelSections.
-    auto SecIt = std::find(PendingLabelSections.begin(),
-                           PendingLabelSections.end(), CurSection);
-    if (SecIt == PendingLabelSections.end())
-      PendingLabelSections.push_back(CurSection);
-  }
-  else
+    PendingLabelSections.insert(CurSection);
+  } else
     // There is no Section / Subsection for this label yet.
     PendingLabels.push_back(S);
 }