revert recent patch which is causing widespread breakage.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52415 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/IPConstantPropagation.cpp

@@ -21,7 +21,6 @@
 #include "llvm/Instructions.h"
 #include "llvm/Module.h"
 #include "llvm/Pass.h"
-#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Support/CallSite.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/ADT/Statistic.h"
@@ -141,14 +140,9 @@ bool IPCP::PropagateConstantsIntoArguments(Function &F) {
 }
 
 
-// Check to see if this function returns one or more constants. If so, replace
-// all callers that use those return values with the constant value. This will
-// leave in the actual return values and instructions, but deadargelim will
-// clean that up.
-//
-// Additionally if a function always returns one of its arguments directly,
-// callers will be updated to use the value they pass in directly instead of
-// using the return value.
+// Check to see if this function returns a constant.  If so, replace all callers
+// that user the return value with the returned valued.  If we can replace ALL
+// callers,
 bool IPCP::PropagateConstantReturn(Function &F) {
   if (F.getReturnType() == Type::VoidTy)
     return false; // No return value.
@@ -162,65 +156,48 @@ bool IPCP::PropagateConstantReturn(Function &F) {
   SmallVector<Value *,4> RetVals;
   const StructType *STy = dyn_cast<StructType>(F.getReturnType());
   if (STy)
-    for (unsigned i = 0, e = STy->getNumElements(); i < e; ++i) 
-      RetVals.push_back(UndefValue::get(STy->getElementType(i)));
+    RetVals.assign(STy->getNumElements(), 0);
   else
-    RetVals.push_back(UndefValue::get(F.getReturnType()));
+    RetVals.push_back(0);
 
-  unsigned NumNonConstant = 0;
   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
     if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
-      // Return type does not match operand type, this is an old style multiple
-      // return
-      bool OldReturn = (F.getReturnType() != RI->getOperand(0)->getType());
-
+      assert(RetVals.size() == RI->getNumOperands() &&
+             "Invalid ReturnInst operands!");
       for (unsigned i = 0, e = RetVals.size(); i != e; ++i) {
-        // Already found conflicting return values?
+        if (isa<UndefValue>(RI->getOperand(i)))
+          continue; // Ignore
+        Constant *C = dyn_cast<Constant>(RI->getOperand(i));
+        if (C == 0)
+          return false; // Does not return a constant.
+        
         Value *RV = RetVals[i];
-        if (!RV)
-          continue;
-
-        // Find the returned value
-        Value *V;
-        if (!STy || OldReturn)
-          V = RI->getOperand(i);
-        else
-          V = FindInsertedValue(RI->getOperand(0), i);
-
-        if (V) {
-          // Ignore undefs, we can change them into anything
-          if (isa<UndefValue>(V))
-            continue;
-          
-          // Try to see if all the rets return the same constant or argument.
-          if (isa<Constant>(V) || isa<Argument>(V)) {
-            if (isa<UndefValue>(RV)) {
-              // No value found yet? Try the current one.
-              RetVals[i] = V;
-              continue;
-            }
-            // Returning the same value? Good.
-            if (RV == V)
-              continue;
-          }
-        }
-        // Different or no known return value? Don't propagate this return
-        // value.
-        RetVals[i] = 0;
-        // All values non constant? Stop looking.
-        if (++NumNonConstant == RetVals.size())
-          return false;
+        if (RV == 0)
+          RetVals[i] = C;
+        else if (RV != C)
+          return false; // Does not return the same constant.
       }
     }
 
-  // If we got here, the function returns at least one constant value.  Loop
-  // over all users, replacing any uses of the return value with the returned
-  // constant.
+  if (STy) {
+    for (unsigned i = 0, e = RetVals.size(); i < e; ++i) 
+      if (RetVals[i] == 0) 
+        RetVals[i] = UndefValue::get(STy->getElementType(i));
+  } else {
+    assert(RetVals.size() == 1);
+    if (RetVals[0] == 0)
+      RetVals[0] = UndefValue::get(F.getReturnType());
+  }
+
+  // If we got here, the function returns a constant value.  Loop over all
+  // users, replacing any uses of the return value with the returned constant.
+  bool ReplacedAllUsers = true;
   bool MadeChange = false;
   for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
     // Make sure this is an invoke or call and that the use is for the callee.
     if (!(isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) ||
         UI.getOperandNo() != 0) {
+      ReplacedAllUsers = false;
       continue;
     }
     
@@ -235,37 +212,28 @@ bool IPCP::PropagateConstantReturn(Function &F) {
       continue;
     }
    
-    for (Value::use_iterator I = Call->use_begin(), E = Call->use_end();
-         I != E;) {
-      Instruction *Ins = dyn_cast<Instruction>(*I);
+    while (!Call->use_empty()) {
+      GetResultInst *GR = cast<GetResultInst>(Call->use_back());
+      GR->replaceAllUsesWith(RetVals[GR->getIndex()]);
+      GR->eraseFromParent();
+    }
+  }
   
-      // Increment now, so we can remove the use
-      ++I;
-
-      // Not an instruction? Ignore
-      if (!Ins)
-        continue;
-
-      // Find the index of the retval to replace with
-      int index = -1;
-      if (GetResultInst *GR = dyn_cast<GetResultInst>(Ins))
-        index = GR->getIndex();
-      else if (ExtractValueInst *EV = dyn_cast<ExtractValueInst>(Ins))
-        if (EV->hasIndices())
-          index = *EV->idx_begin();
-
-      // If this use uses a specific return value, and we have a replacement,
-      // replace it.
-      if (index != -1) {
-        Value *New = RetVals[index];
-        if (New) {
-          if (Argument *A = dyn_cast<Argument>(New))
-            // Was an argument returned? Then find the corresponding argument in
-            // the call instruction and use that. Add 1 to the argument number
-            // to skipp the first argument (the function itself).
-            New = Call->getOperand(A->getArgNo() + 1);
-          Ins->replaceAllUsesWith(New);
-          Ins->eraseFromParent();
+  // If we replace all users with the returned constant, and there can be no
+  // other callers of the function, replace the constant being returned in the
+  // function with an undef value.
+  if (ReplacedAllUsers && F.hasInternalLinkage()) {
+    for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
+      if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
+        for (unsigned i = 0, e = RetVals.size(); i < e; ++i) {
+          Value *RetVal = RetVals[i];
+          if (isa<UndefValue>(RetVal))
+            continue;
+          Value *RV = UndefValue::get(RetVal->getType());
+          if (RI->getOperand(i) != RV) {
+            RI->setOperand(i, RV);
+            MadeChange = true;
+          }
         }
       }
     }