Enable Local CSE by default

src/IceCfg.cpp

Index: src/IceCfg.cpp
diff --git a/src/IceCfg.cpp b/src/IceCfg.cpp
index 23c363fa7791938a5a05a0edfc6adaf72167f48b..c20b9fc303dcdca399d24cdd2a6687a7f4622912 100644
--- a/src/IceCfg.cpp
+++ b/src/IceCfg.cpp
@@ -572,7 +572,7 @@ void Cfg::localCSE() {
       return true;
     }
   };
-
+  bool NoSSA = getFlags().getLocalCSENoSSA();

[John, 2016/07/28 14:21:50]

const bool

[manasijm, 2016/07/28 19:43:34]

Done.

   for (CfgNode *Node : getNodes()) {
     CfgUnorderedSet<Inst *, InstHash, InstEq> Seen;
 
@@ -581,8 +581,7 @@ void Cfg::localCSE() {
     // memory but will be slower i.e map of Instruction -> Set of Variables
 
     CfgUnorderedMap<Variable *, std::vector<Inst *>, VariableHash> Dependency;
-    // Not necessary for SSA, still keeping it in case this pass is not run at
-    // the beginning. Remove to improve performace.
+    // Not necessary for SSA
 
     int IterCount = getFlags().getLocalCseMaxIterations();
 
@@ -591,25 +590,24 @@ void Cfg::localCSE() {
       for (Inst &Instr : Node->getInsts()) {
         if (Instr.isDeleted() || !llvm::isa<InstArithmetic>(&Instr))
           continue;
+        if (NoSSA) {

[John, 2016/07/28 14:21:50]

document what's going on here. why is this needed for non-SSA IR?

[manasijm, 2016/07/28 15:24:44]

This is needed if this pass is moved to a point later in the pipeline.
If Variables have a single definition in the block, CSE can work just on the
basis of an equality compare on instructions (sans Dest). When variables can be
updated (hence, non-SSA) the result of a previous instruction which used that
variable can not be reused.
(Will put this as a comment here.)

[manasijm, 2016/07/28 19:43:33]

Done.

+          // Invalidate replacements
+          auto Iter = Replacements.find(Instr.getDest());
+          if (Iter != Replacements.end()) {
+            Replacements.erase(Iter);
+          }
 
-        // Invalidate replacements
-        auto Iter = Replacements.find(Instr.getDest());
-        if (Iter != Replacements.end()) {
-          Replacements.erase(Iter);
-        }
-
-        // Invalidate 'seen' instructions whose operands were just updated.
-        auto DepIter = Dependency.find(Instr.getDest());
-        if (DepIter != Dependency.end()) {
-          for (auto DepInst : DepIter->second) {
-            Seen.erase(DepInst);
+          // Invalidate 'seen' instructions whose operands were just updated.
+          auto DepIter = Dependency.find(Instr.getDest());
+          if (DepIter != Dependency.end()) {
+            for (auto DepInst : DepIter->second) {

[John, 2016/07/28 14:21:50]

auto *

[manasijm, 2016/07/28 19:43:34]

Done.

+              Seen.erase(DepInst);
+            }
           }
         }
-        // The above two can be removed if SSA is assumed.
 
         // Replace - doing this before checking for repetitions might enable
-        // more
-        // optimizations
+        // more optimizations
         for (SizeT i = 0; i < Instr.getSrcSize(); ++i) {
           auto *Opnd = Instr.getSrc(i);
           if (auto *Var = llvm::dyn_cast<Variable>(Opnd)) {
@@ -627,11 +625,13 @@ void Cfg::localCSE() {
         } else { // new
           Seen.insert(&Instr);
 
-          // Update dependencies
-          for (SizeT i = 0; i < Instr.getSrcSize(); ++i) {
-            auto *Opnd = Instr.getSrc(i);
-            if (auto *Var = llvm::dyn_cast<Variable>(Opnd)) {
-              Dependency[Var].push_back(&Instr);
+          if (NoSSA) {
+            // Update dependencies
+            for (SizeT i = 0; i < Instr.getSrcSize(); ++i) {
+              auto *Opnd = Instr.getSrc(i);
+              if (auto *Var = llvm::dyn_cast<Variable>(Opnd)) {
+                Dependency[Var].push_back(&Instr);
+              }
             }
           }
         }