Reapply r68211, with the miscompilations it caused fixed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68262 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/GVN.cpp

@@ -1294,9 +1294,28 @@ bool GVN::processInstruction(Instruction *I,
   uint32_t nextNum = VN.getNextUnusedValueNumber();
   unsigned num = VN.lookup_or_add(I);
   
+  if (BranchInst* BI = dyn_cast<BranchInst>(I)) {
+    localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
+    
+    if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
+      return false;
+    
+    Value* branchCond = BI->getCondition();
+    uint32_t condVN = VN.lookup_or_add(branchCond);
+    
+    BasicBlock* trueSucc = BI->getSuccessor(0);
+    BasicBlock* falseSucc = BI->getSuccessor(1);
+    
+    if (trueSucc->getSinglePredecessor())
+      localAvail[trueSucc]->table[condVN] = ConstantInt::getTrue();
+    if (falseSucc->getSinglePredecessor())
+      localAvail[falseSucc]->table[condVN] = ConstantInt::getFalse();
+
+    return false;
+    
   // Allocations are always uniquely numbered, so we can save time and memory
   // by fast failing them.  
-  if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
+  } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
     localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
     return false;
   }
@@ -1405,18 +1424,11 @@ bool GVN::runOnFunction(Function& F) {
 
 
 bool GVN::processBlock(BasicBlock* BB) {
-  DomTreeNode* DTN = DT->getNode(BB);
   // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
   // incrementing BI before processing an instruction).
   SmallVector<Instruction*, 8> toErase;
   bool changed_function = false;
   
-  if (DTN->getIDom())
-    localAvail[BB] =
-                  new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]);
-  else
-    localAvail[BB] = new ValueNumberScope(0);
-  
   for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
        BI != BE;) {
     changed_function |= processInstruction(BI, toErase);
@@ -1607,6 +1619,15 @@ bool GVN::performPRE(Function& F) {
 bool GVN::iterateOnFunction(Function &F) {
   cleanupGlobalSets();
 
+  for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
+       DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
+    if (DI->getIDom())
+      localAvail[DI->getBlock()] =
+                   new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
+    else
+      localAvail[DI->getBlock()] = new ValueNumberScope(0);
+  }
+
   // Top-down walk of the dominator tree
   bool changed = false;
 #if 0

test/Transforms/GVN/condprop.ll

@@ -0,0 +1,52 @@
+; RUN: llvm-as < %s | opt -gvn | llvm-dis | grep {br i1 false}
+
+@a = external global i32		; <i32*> [#uses=7]
+
+define i32 @foo() nounwind {
+entry:
+	%0 = load i32* @a, align 4		; <i32> [#uses=1]
+	%1 = icmp eq i32 %0, 4		; <i1> [#uses=1]
+	br i1 %1, label %bb, label %bb1
+
+bb:		; preds = %entry
+	br label %bb8
+
+bb1:		; preds = %entry
+	%2 = load i32* @a, align 4		; <i32> [#uses=1]
+	%3 = icmp eq i32 %2, 5		; <i1> [#uses=1]
+	br i1 %3, label %bb2, label %bb3
+
+bb2:		; preds = %bb1
+	br label %bb8
+
+bb3:		; preds = %bb1
+	%4 = load i32* @a, align 4		; <i32> [#uses=1]
+	%5 = icmp eq i32 %4, 4		; <i1> [#uses=1]
+	br i1 %5, label %bb4, label %bb5
+
+bb4:		; preds = %bb3
+	%6 = load i32* @a, align 4		; <i32> [#uses=1]
+	%7 = add i32 %6, 5		; <i32> [#uses=1]
+	br label %bb8
+
+bb5:		; preds = %bb3
+	%8 = load i32* @a, align 4		; <i32> [#uses=1]
+	%9 = icmp eq i32 %8, 5		; <i1> [#uses=1]
+	br i1 %9, label %bb6, label %bb7
+
+bb6:		; preds = %bb5
+	%10 = load i32* @a, align 4		; <i32> [#uses=1]
+	%11 = add i32 %10, 4		; <i32> [#uses=1]
+	br label %bb8
+
+bb7:		; preds = %bb5
+	%12 = load i32* @a, align 4		; <i32> [#uses=1]
+	br label %bb8
+
+bb8:		; preds = %bb7, %bb6, %bb4, %bb2, %bb
+	%.0 = phi i32 [ %12, %bb7 ], [ %11, %bb6 ], [ %7, %bb4 ], [ 4, %bb2 ], [ 5, %bb ]		; <i32> [#uses=1]
+	br label %return
+
+return:		; preds = %bb8
+	ret i32 %.0
+}