Small performance improvement in generated C code:

Instead of unconditionally copying all phi node values into temporaries for
all successor blocks, generate code that will determine what successor
block will be called and then copy only those phi node values needed by
the successor block.

This seems to cut down namd execution time from being 8% higher than GCC to
4% higher than GCC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17144 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/CBackend/CBackend.cpp b/lib/Target/CBackend/CBackend.cpp
index 9e835f6093bfc066715758da102e16cd5bbc5b8c..7af9bfe4fa6b6d566bc9f8b478d767d781850c95 100644 (file)
--- a/lib/Target/CBackend/CBackend.cpp
+++ b/lib/Target/CBackend/CBackend.cpp
@@ -204,6 +204,8 @@ namespace {
     }
 
     bool isGotoCodeNecessary(BasicBlock *From, BasicBlock *To);
+    void printPHICopiesForSuccessor(BasicBlock *CurBlock,
+                                    BasicBlock *Successor, unsigned Indent);
     void printPHICopiesForSuccessors(BasicBlock *CurBlock, 
                                      unsigned Indent);
     void printBranchToBlock(BasicBlock *CurBlock, BasicBlock *SuccBlock,
@@ -1230,6 +1232,23 @@ bool CWriter::isGotoCodeNecessary(BasicBlock *From, BasicBlock *To) {
   return false;
 }
 
+void CWriter::printPHICopiesForSuccessor (BasicBlock *CurBlock,
+                                          BasicBlock *Successor, 
+                                          unsigned Indent) {
+  for (BasicBlock::iterator I = Successor->begin(); isa<PHINode>(I); ++I) {
+    PHINode *PN = cast<PHINode>(I);
+    // Now we have to do the printing.
+    Value *IV = PN->getIncomingValueForBlock(CurBlock);
+    if (!isa<UndefValue>(IV)) {
+      Out << std::string(Indent, ' ');
+      Out << "  " << Mang->getValueName(I) << "__PHI_TEMPORARY = ";
+      writeOperand(IV);
+      Out << ";   /* for PHI node */\n";
+    }
+  }
+}
+
+
 void CWriter::printPHICopiesForSuccessors(BasicBlock *CurBlock, 
                                           unsigned Indent) {
   for (succ_iterator SI = succ_begin(CurBlock), E = succ_end(CurBlock);
@@ -1261,7 +1280,6 @@ void CWriter::printBranchToBlock(BasicBlock *CurBB, BasicBlock *Succ,
 // that immediately succeeds the current one.
 //
 void CWriter::visitBranchInst(BranchInst &I) {
-  printPHICopiesForSuccessors(I.getParent(), 0);
 
   if (I.isConditional()) {
     if (isGotoCodeNecessary(I.getParent(), I.getSuccessor(0))) {
@@ -1269,10 +1287,12 @@ void CWriter::visitBranchInst(BranchInst &I) {
       writeOperand(I.getCondition());
       Out << ") {\n";
       
+      printPHICopiesForSuccessor (I.getParent(), I.getSuccessor(0), 2);
       printBranchToBlock(I.getParent(), I.getSuccessor(0), 2);
       
       if (isGotoCodeNecessary(I.getParent(), I.getSuccessor(1))) {
         Out << "  } else {\n";
+        printPHICopiesForSuccessor (I.getParent(), I.getSuccessor(1), 2);
         printBranchToBlock(I.getParent(), I.getSuccessor(1), 2);
       }
     } else {
@@ -1281,11 +1301,13 @@ void CWriter::visitBranchInst(BranchInst &I) {
       writeOperand(I.getCondition());
       Out << ") {\n";
 
+      printPHICopiesForSuccessor (I.getParent(), I.getSuccessor(1), 2);
       printBranchToBlock(I.getParent(), I.getSuccessor(1), 2);
     }
 
     Out << "  }\n";
   } else {
+    printPHICopiesForSuccessor (I.getParent(), I.getSuccessor(0), 0);
     printBranchToBlock(I.getParent(), I.getSuccessor(0), 0);
   }
   Out << "\n";

diff --git a/lib/Target/CBackend/Writer.cpp b/lib/Target/CBackend/Writer.cpp
index 9e835f6093bfc066715758da102e16cd5bbc5b8c..7af9bfe4fa6b6d566bc9f8b478d767d781850c95 100644 (file)
--- a/lib/Target/CBackend/Writer.cpp
+++ b/lib/Target/CBackend/Writer.cpp
@@ -204,6 +204,8 @@ namespace {
     }
 
     bool isGotoCodeNecessary(BasicBlock *From, BasicBlock *To);
+    void printPHICopiesForSuccessor(BasicBlock *CurBlock,
+                                    BasicBlock *Successor, unsigned Indent);
     void printPHICopiesForSuccessors(BasicBlock *CurBlock, 
                                      unsigned Indent);
     void printBranchToBlock(BasicBlock *CurBlock, BasicBlock *SuccBlock,
@@ -1230,6 +1232,23 @@ bool CWriter::isGotoCodeNecessary(BasicBlock *From, BasicBlock *To) {
   return false;
 }
 
+void CWriter::printPHICopiesForSuccessor (BasicBlock *CurBlock,
+                                          BasicBlock *Successor, 
+                                          unsigned Indent) {
+  for (BasicBlock::iterator I = Successor->begin(); isa<PHINode>(I); ++I) {
+    PHINode *PN = cast<PHINode>(I);
+    // Now we have to do the printing.
+    Value *IV = PN->getIncomingValueForBlock(CurBlock);
+    if (!isa<UndefValue>(IV)) {
+      Out << std::string(Indent, ' ');
+      Out << "  " << Mang->getValueName(I) << "__PHI_TEMPORARY = ";
+      writeOperand(IV);
+      Out << ";   /* for PHI node */\n";
+    }
+  }
+}
+
+
 void CWriter::printPHICopiesForSuccessors(BasicBlock *CurBlock, 
                                           unsigned Indent) {
   for (succ_iterator SI = succ_begin(CurBlock), E = succ_end(CurBlock);
@@ -1261,7 +1280,6 @@ void CWriter::printBranchToBlock(BasicBlock *CurBB, BasicBlock *Succ,
 // that immediately succeeds the current one.
 //
 void CWriter::visitBranchInst(BranchInst &I) {
-  printPHICopiesForSuccessors(I.getParent(), 0);
 
   if (I.isConditional()) {
     if (isGotoCodeNecessary(I.getParent(), I.getSuccessor(0))) {
@@ -1269,10 +1287,12 @@ void CWriter::visitBranchInst(BranchInst &I) {
       writeOperand(I.getCondition());
       Out << ") {\n";
       
+      printPHICopiesForSuccessor (I.getParent(), I.getSuccessor(0), 2);
       printBranchToBlock(I.getParent(), I.getSuccessor(0), 2);
       
       if (isGotoCodeNecessary(I.getParent(), I.getSuccessor(1))) {
         Out << "  } else {\n";
+        printPHICopiesForSuccessor (I.getParent(), I.getSuccessor(1), 2);
         printBranchToBlock(I.getParent(), I.getSuccessor(1), 2);
       }
     } else {
@@ -1281,11 +1301,13 @@ void CWriter::visitBranchInst(BranchInst &I) {
       writeOperand(I.getCondition());
       Out << ") {\n";
 
+      printPHICopiesForSuccessor (I.getParent(), I.getSuccessor(1), 2);
       printBranchToBlock(I.getParent(), I.getSuccessor(1), 2);
     }
 
     Out << "  }\n";
   } else {
+    printPHICopiesForSuccessor (I.getParent(), I.getSuccessor(0), 0);
     printBranchToBlock(I.getParent(), I.getSuccessor(0), 0);
   }
   Out << "\n";