Use the new addEscapingValue callback to update GlobalsModRef when GVN adds PHIs of GEPs. For the moment,

have GlobalsModRef handle this conservatively by simply removing the value from its maps.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122787 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 31 insertions, 2 deletions

diff --git a/lib/Analysis/IPA/GlobalsModRef.cpp b/lib/Analysis/IPA/GlobalsModRef.cpp
index c18dc47406..116aaf418e 100644
--- a/lib/Analysis/IPA/GlobalsModRef.cpp
+++ b/lib/Analysis/IPA/GlobalsModRef.cpp
@@ -152,6 +152,7 @@ namespace {
 
     virtual void deleteValue(Value *V);
     virtual void copyValue(Value *From, Value *To);
+    virtual void addEscapingUse(Use &U);
 
     /// getAdjustedAnalysisPointer - This method is used when a pass implements
     /// an analysis interface through multiple inheritance.  If needed, it
@@ -596,3 +597,13 @@ void GlobalsModRef::deleteValue(Value *V) {
 void GlobalsModRef::copyValue(Value *From, Value *To) {
   AliasAnalysis::copyValue(From, To);
 }
+
+void GlobalsModRef::addEscapingUse(Use &U) {
+  // For the purposes of this analysis, it is conservatively correct to treat
+  // a newly escaping value equivalently to a deleted one.  We could perhaps
+  // be more precise by processing the new use and attempting to update our
+  // saved analysis results to accomodate it.
+  deleteValue(U);
+  
+  AliasAnalysis::addEscapingUse(U);
+}
diff --git a/lib/Analysis/NoAliasAnalysis.cpp b/lib/Analysis/NoAliasAnalysis.cpp
index ab7a69241e..101c2d5b02 100644
--- a/lib/Analysis/NoAliasAnalysis.cpp
+++ b/lib/Analysis/NoAliasAnalysis.cpp
@@ -65,6 +65,7 @@ namespace {
 
     virtual void deleteValue(Value *V) {}
     virtual void copyValue(Value *From, Value *To) {}
+    virtual void addEscapingUse(Use &U) {}
     
     /// getAdjustedAnalysisPointer - This method is used when a pass implements
     /// an analysis interface through multiple inheritance.  If needed, it
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index bf46bd98c3..f0e0f38142 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -1063,6 +1063,15 @@ static Value *ConstructSSAForLoadSet(LoadInst *LI,
   if (V->getType()->isPointerTy())
     for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
       AA->copyValue(LI, NewPHIs[i]);
+    
+    // Now that we've copied information to the new PHIs, scan through
+    // them again and inform alias analysis that we've added potentially
+    // escaping uses to any values that are operands to these PHIs.
+    for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) {
+      PHINode *P = NewPHIs[i];
+      for (unsigned ii = 0, ee = P->getNumIncomingValues(); ii != ee; ++ii)
+        AA->addEscapingUse(P->getOperandUse(2*ii));
+    }
 
   return V;
 }
@@ -1957,8 +1966,16 @@ bool GVN::performPRE(Function &F) {
       insert_table(ValNo, Phi, CurrentBlock);
 
       CurInst->replaceAllUsesWith(Phi);
-      if (MD && Phi->getType()->isPointerTy())
-        MD->invalidateCachedPointerInfo(Phi);
+      if (Phi->getType()->isPointerTy()) {
+        // Because we have added a PHI-use of the pointer value, it has now
+        // "escaped" from alias analysis' perspective.  We need to inform
+        // AA of this.
+        for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee; ++ii)
+          VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(2*ii));
+        
+        if (MD)
+          MD->invalidateCachedPointerInfo(Phi);
+      }
       VN.erase(CurInst);
       erase_table(ValNo, CurInst, CurrentBlock);