[llvm-commits] [llvm] r53108 - /llvm/trunk/lib/Transforms/Scalar/GVN.cpp

Owen Anderson resistor at mac.com
Thu Jul 3 10:44:34 PDT 2008


Author: resistor
Date: Thu Jul  3 12:44:33 2008
New Revision: 53108

URL: http://llvm.org/viewvc/llvm-project?rev=53108&view=rev
Log:
Use information already present in the ValueTable to fast-fail when we know there won't be a value number match.  This speeds up GVN on a case where there are very few redundancies by ~25%.

Modified:
    llvm/trunk/lib/Transforms/Scalar/GVN.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=53108&r1=53107&r2=53108&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Thu Jul  3 12:44:33 2008
@@ -166,6 +166,7 @@
       void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
       void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
       void setDomTree(DominatorTree* D) { DT = D; }
+      uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
   };
 }
 
@@ -1058,11 +1059,12 @@
     return changed;
   }
   
+  uint32_t nextNum = VN.getNextUnusedValueNumber();
   unsigned num = VN.lookup_or_add(I);
   
   // Allocations are always uniquely numbered, so we can save time and memory
   // by fast failing them.
-  if (isa<AllocationInst>(I)) {
+  if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
     localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
     return false;
   }
@@ -1082,6 +1084,13 @@
     } else {
       localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
     }
+  
+  // If the number we were assigned was a brand new VN, then we don't
+  // need to do a lookup to see if the number already exists
+  // somewhere in the domtree: it can't!
+  } else if (num == nextNum) {
+    localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
+    
   // Perform value-number based elimination
   } else if (Value* repl = lookupNumber(I->getParent(), num)) {
     // Remove it!
@@ -1092,7 +1101,7 @@
     I->replaceAllUsesWith(repl);
     toErase.push_back(I);
     return true;
-  } else if (!I->isTerminator()) {
+  } else {
     localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
   }
   





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