Subzero: Speed up VariablesMetadata initialization.

src/IceRegAlloc.cpp

 //===- subzero/src/IceRegAlloc.cpp - Linear-scan implementation -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the LinearScan class, which performs the
@@ skipping 14 matching lines @@
 
 // Returns true if Var has any definitions within Item's live range.
 // TODO(stichnot): Consider trimming the Definitions list similar to
 // how the live ranges are trimmed, since all the overlapsDefs() tests
 // are whether some variable's definitions overlap Cur, and trimming
 // is with respect Cur.start.  Initial tests show no measurable
 // performance difference, so we'll keep the code simple for now.
 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;
   }
   return false;
 }
 
 void dumpDisableOverlap(const Cfg *Func, const Variable *Var,
                         const char *Reason) {
   if (Func->getContext()->isVerbose(IceV_LinearScan)) {
     VariablesMetadata *VMetadata = Func->getVMetadata();
     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";
   }
 }
 
 void dumpLiveRange(const Variable *Var, const Cfg *Func) {
   Ostream &Str = Func->getContext()->getStrDump();
   const static size_t BufLen = 30;
   char buf[BufLen];
   snprintf(buf, BufLen, "%2d", Var->getRegNumTmp());
@@ skipping 504 matching lines @@
     Str << "\n";
   }
   Str << "++++++ Inactive:\n";
   for (const Variable *Item : Inactive) {
     dumpLiveRange(Item, Func);
     Str << "\n";
   }
 }
 
 } // end of namespace Ice