Subzero: Speed up VariablesMetadata initialization.

src/IceRegAlloc.cpp

Index: src/IceRegAlloc.cpp
diff --git a/src/IceRegAlloc.cpp b/src/IceRegAlloc.cpp
index b5c3315c4218636ffe05fa7bb559b265853cf2c4..1b4d0c249d0d872f2aecb705081dce83e25a04c8 100644
--- a/src/IceRegAlloc.cpp
+++ b/src/IceRegAlloc.cpp
@@ -32,7 +32,10 @@ namespace {
 bool overlapsDefs(const Cfg *Func, const Variable *Item, const Variable *Var) {
   const bool UseTrimmed = true;
   VariablesMetadata *VMetadata = Func->getVMetadata();
-  const InstDefList &Defs = VMetadata->getDefinitions(Var);
+  if (const Inst *FirstDef = VMetadata->getFirstDefinition(Var))
+    if (Item->getLiveRange().overlapsInst(FirstDef->getNumber(), UseTrimmed))
+      return true;
+  const InstDefList &Defs = VMetadata->getLatterDefinitions(Var);
   for (size_t i = 0; i < Defs.size(); ++i) {
     if (Item->getLiveRange().overlapsInst(Defs[i]->getNumber(), UseTrimmed))
       return true;
@@ -47,11 +50,11 @@ void dumpDisableOverlap(const Cfg *Func, const Variable *Var,
     Ostream &Str = Func->getContext()->getStrDump();
     Str << "Disabling Overlap due to " << Reason << " " << *Var
         << " LIVE=" << Var->getLiveRange() << " Defs=";
-    const InstDefList &Defs = VMetadata->getDefinitions(Var);
+    if (const Inst *FirstDef = VMetadata->getFirstDefinition(Var))
+      Str << FirstDef->getNumber();
+    const InstDefList &Defs = VMetadata->getLatterDefinitions(Var);
     for (size_t i = 0; i < Defs.size(); ++i) {

[jvoung (off chromium), 2014/10/15 22:10:37]

Might be able to use a range-based for-loop now that "i > 0" isn't checked?

[Jim Stichnoth, 2014/10/15 22:12:44]

Yeah, though I was thinking of making one big pass over the code to change most
or all loops involving std::vector.size() to be range-based.

-      if (i > 0)
-        Str << ",";
-      Str << Defs[i]->getNumber();
+      Str << "," << Defs[i]->getNumber();
     }
     Str << "\n";
   }