Fix: ConstantMerge/2002-09-23-CPR-Update.ll

Basically, this bug boiled down to calling replaceUsesOfWith on a constant,
which changed it's shape in an illegal way.  This pass now goes through all
of the trouble neccesary to do the replacement on constants.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3895 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/ConstantMerge.cpp

@@ -3,19 +3,16 @@
 // This file defines the interface to a pass that merges duplicate global
 // constants together into a single constant that is shared.  This is useful
 // because some passes (ie TraceValues) insert a lot of string constants into
-// the program, regardless of whether or not they duplicate an existing string.
+// the program, regardless of whether or not an existing string is available.
 //
 // Algorithm: ConstantMerge is designed to build up a map of available constants
-// and elminate duplicates when it is initialized.
-//
-// The DynamicConstantMerge method is a superset of the ConstantMerge algorithm
-// that checks for each function to see if constants have been added to the
-// constant pool since it was last run... if so, it processes them.
+// and eliminate duplicates when it is initialized.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Module.h"
+#include "llvm/Constants.h"
 #include "llvm/Pass.h"
 #include "Support/StatisticReporter.h"
 
@@ -26,9 +23,9 @@ namespace {
     //
     bool run(Module &M);
 
-    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
-      AU.preservesCFG();
-    }
+  private:
+    void replaceUsesOfWith(GlobalVariable *Old, GlobalVariable *New);
+    void replaceConstantWith(Constant *Old, Constant *New);
   };
 
   Statistic<> NumMerged("constmerge\t\t- Number of global constants merged");
@@ -38,10 +35,6 @@ namespace {
 Pass *createConstantMergePass() { return new ConstantMerge(); }
 
 
-// ConstantMerge::run - Workhorse for the pass.  This eliminates duplicate
-// constants, starting at global ConstantNo, and adds vars to the map if they
-// are new and unique.
-//
 bool ConstantMerge::run(Module &M) {
   std::map<Constant*, GlobalVariable*> CMap;
   bool MadeChanges = false;
@@ -58,7 +51,7 @@ bool ConstantMerge::run(Module &M) {
         CMap.insert(I, std::make_pair(Init, GV));
       } else {                  // Yup, this is a duplicate!
         // Make all uses of the duplicate constant use the cannonical version...
-        GV->replaceAllUsesWith(I->second);
+        replaceUsesOfWith(GV, I->second);
 
         // Delete the global value from the module... and back up iterator to
         // not skip the next global...
@@ -71,3 +64,98 @@ bool ConstantMerge::run(Module &M) {
 
   return MadeChanges;
 }
+
+/// replaceUsesOfWith - Replace all uses of Old with New.  For instructions,
+/// this is a really simple matter of replacing the reference to Old with a
+/// reference to New.  For constants references, however, we must carefully
+/// build replacement constants to substitute in.
+///
+void ConstantMerge::replaceUsesOfWith(GlobalVariable *Old, GlobalVariable *New){
+  while (!Old->use_empty()) {
+    User *U = Old->use_back();
+    if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(U))
+      replaceConstantWith(CPR, ConstantPointerRef::get(New));
+    else
+      U->replaceUsesOfWith(Old, New);
+  }
+}
+
+/// replaceWith - Ok, so we have a constant 'Old' and we want to replace it with
+/// 'New'.  To do this, we have to recursively go through the uses of Old,
+/// replacing them with new things.  The problem is that if a constant uses Old,
+/// then we need to replace the uses of the constant with uses of the equivalent
+/// constant that uses New instead.
+///
+void ConstantMerge::replaceConstantWith(Constant *Old, Constant *New) {
+  while (!Old->use_empty()) {
+    User *U = Old->use_back();
+
+    if (Constant *C = dyn_cast<Constant>(U)) {
+      Constant *Replacement = 0;
+      
+      // Depending on the type of constant, build a suitable replacement...
+      if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
+        if (CE->getOpcode() == Instruction::GetElementPtr) {
+          std::vector<Constant*> Indices;
+          Constant *Pointer = cast<Constant>(CE->getOperand(0));
+          Indices.reserve(CE->getNumOperands()-1);
+          if (Pointer == Old) Pointer = New;
+
+          for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) {
+            Constant *Val = cast<Constant>(CE->getOperand(i));
+            if (Val == Old) Val = New;
+            Indices.push_back(Val);
+          }
+          Replacement = ConstantExpr::getGetElementPtr(Pointer, Indices);
+        } else if (CE->getOpcode() == Instruction::Cast) {
+          assert(CE->getOperand(0) == Old && "Cast only has one use!");
+          Replacement = ConstantExpr::getCast(New, CE->getType());
+        } else if (CE->getNumOperands() == 2) {
+          Constant *C1 = cast<Constant>(CE->getOperand(0));
+          Constant *C2 = cast<Constant>(CE->getOperand(1));
+          if (C1 == Old) C1 = New;
+          if (C2 == Old) C2 = New;
+          Replacement = ConstantExpr::get(CE->getOpcode(), C1, C2);
+        } else {
+          assert(0 && "Unknown ConstantExpr type!");
+        }
+
+
+      } else if (ConstantArray *CA = dyn_cast<ConstantArray>(C)) {
+        std::vector<Constant*> Values;
+        Values.reserve(CA->getValues().size());
+        for (unsigned i = 0, e = CA->getValues().size(); i != e; ++i) {
+          Constant *Val = cast<Constant>(CA->getValues()[i]);
+          if (Val == Old) Val = New;
+          Values.push_back(Val);
+        }
+
+        Replacement = ConstantArray::get(CA->getType(), Values);
+      } else if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
+        std::vector<Constant*> Values;
+        Values.reserve(CS->getValues().size());
+
+        for (unsigned i = 0, e = CS->getValues().size(); i != e; ++i) {
+          Constant *Val = cast<Constant>(CS->getValues()[i]);
+          if (Val == Old) Val = New;
+          Values.push_back(Val);
+        }
+
+        Replacement = ConstantStruct::get(CS->getType(), Values);
+      } else {
+        assert(0 && "Unexpected/unknown constant type!");
+      }
+      
+      // Now that we have a suitable replacement, recursively eliminate C.
+      replaceConstantWith(C, Replacement);
+
+    } else {
+      // If it is not a constant, we can simply replace uses of Old with New.
+      U->replaceUsesOfWith(Old, New);
+    }
+
+  }
+
+  // No-one refers to this old dead constant now, destroy it!
+  Old->destroyConstant();
+}