Rather than marking all internal globals "Ref"

when a readonly declaration is called, set a
flag.  This is faster and uses less memory.
In theory it is less accurate, because before
only those internal globals that were read
by someone were being marked "Ref", but now
all are.  But in practice, thanks to other
passes, all internal globals of the kind
considered here will be both read and stored
to: those only read will have been turned
into constants, and those only stored to will
have been deleted.

llvm-svn: 56143

1 files changed, 11 insertions, 17 deletions

diff --git a/llvm/lib/Analysis/IPA/GlobalsModRef.cpp b/llvm/lib/Analysis/IPA/GlobalsModRef.cpp
index 6736e6f3ce4..390a6028eb4 100644
--- a/llvm/lib/Analysis/IPA/GlobalsModRef.cpp
+++ b/llvm/lib/Analysis/IPA/GlobalsModRef.cpp
@@ -49,18 +49,22 @@ namespace {
     /// function.
     std::map<GlobalValue*, unsigned> GlobalInfo;
 
+    /// MayReadAnyGlobal - May read global variables, but it is not known which.
+    bool MayReadAnyGlobal;
+
     unsigned getInfoForGlobal(GlobalValue *GV) const {
+      unsigned Effect = MayReadAnyGlobal ? AliasAnalysis::Ref : 0;
       std::map<GlobalValue*, unsigned>::const_iterator I = GlobalInfo.find(GV);
       if (I != GlobalInfo.end())
-        return I->second;
-      return 0;
+        Effect |= I->second;
+      return Effect;
     }
 
     /// FunctionEffect - Capture whether or not this function reads or writes to
     /// ANY memory.  If not, we can do a lot of aggressive analysis on it.
     unsigned FunctionEffect;
 
-    FunctionRecord() : FunctionEffect(0) {}
+    FunctionRecord() : MayReadAnyGlobal (false), FunctionEffect(0) {}
   };
 
   /// GlobalsModRef - The actual analysis pass.
@@ -70,10 +74,6 @@ namespace {
     /// taken.
     std::set<GlobalValue*> NonAddressTakenGlobals;
 
-    /// ReadGlobals - The globals without addresses taken that are read by
-    /// some function.
-    std::set<GlobalValue*> ReadGlobals;
-
     /// IndirectGlobals - The memory pointed to by this global is known to be
     /// 'owned' by the global.
     std::set<GlobalValue*> IndirectGlobals;
@@ -203,10 +203,6 @@ void GlobalsModRef::AnalyzeGlobals(Module &M) {
         // Remember that we are tracking this global, and the mod/ref fns
         NonAddressTakenGlobals.insert(I);
 
-        if (!Readers.empty())
-          // Some function read this global - remember that.
-          ReadGlobals.insert(I);
-
         for (unsigned i = 0, e = Readers.size(); i != e; ++i)
           FunctionInfo[Readers[i]].GlobalInfo[I] |= Ref;
 
@@ -384,13 +380,10 @@ void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
           // Can't do better than that!
         } else if (F->onlyReadsMemory()) {
           FunctionEffect |= Ref;
-          if (!F->isIntrinsic()) {
+          if (!F->isIntrinsic())
             // This function might call back into the module and read a global -
-            // mark all globals read somewhere as being read by this function.
-            for (std::set<GlobalValue*>::iterator GI = ReadGlobals.begin(),
-                 E = ReadGlobals.end(); GI != E; ++GI)
-              FR.GlobalInfo[*GI] |= Ref;
-          }
+            // consider every global as possibly being read by this function.
+            FR.MayReadAnyGlobal = true;
         } else {
           FunctionEffect |= ModRef;
           // Can't say anything useful unless it's an intrinsic - they don't
@@ -412,6 +405,7 @@ void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
                    CalleeFR->GlobalInfo.begin(), E = CalleeFR->GlobalInfo.end();
                  GI != E; ++GI)
               FR.GlobalInfo[GI->first] |= GI->second;
+            FR.MayReadAnyGlobal |= CalleeFR->MayReadAnyGlobal;
           } else {
             // Can't say anything about it.  However, if it is inside our SCC,
             // then nothing needs to be done.