Make ConstantFoldConstantExpression recursively visit the entire

ConstantExpr, not just the top-level operator. This allows it to
fold many more constants.

Also, make GlobalOpt call ConstantFoldConstantExpression on
GlobalVariable initializers.

llvm-svn: 89659

2 files changed, 20 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 1cdadbfcea4..8d60907f8cb 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -671,8 +671,13 @@ Constant *llvm::ConstantFoldInstruction(Instruction *I, const TargetData *TD) {
 Constant *llvm::ConstantFoldConstantExpression(ConstantExpr *CE,
                                                const TargetData *TD) {
   SmallVector<Constant*, 8> Ops;
-  for (User::op_iterator i = CE->op_begin(), e = CE->op_end(); i != e; ++i)
-    Ops.push_back(cast<Constant>(*i));
+  for (User::op_iterator i = CE->op_begin(), e = CE->op_end(); i != e; ++i) {
+    Constant *NewC = cast<Constant>(*i);
+    // Recursively fold the ConstantExpr's operands.
+    if (ConstantExpr *NewCE = dyn_cast<ConstantExpr>(NewC))
+      NewC = ConstantFoldConstantExpression(NewCE, TD);
+    Ops.push_back(NewC);
+  }
 
   if (CE->isCompare())
     return ConstantFoldCompareInstOperands(CE->getPredicate(), Ops[0], Ops[1],
@@ -687,6 +692,10 @@ Constant *llvm::ConstantFoldConstantExpression(ConstantExpr *CE,
 /// attempting to fold instructions like loads and stores, which have no
 /// constant expression form.
 ///
+/// TODO: This function neither utilizes nor preserves nsw/nuw/inbounds/etc
+/// information, due to only being passed an opcode and operands. Constant
+/// folding using this function strips this information.
+///
 Constant *llvm::ConstantFoldInstOperands(unsigned Opcode, const Type *DestTy, 
                                          Constant* const* Ops, unsigned NumOps,
                                          const TargetData *TD) {
diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index 442f2fb6552..4635d0e61c3 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -1898,6 +1898,15 @@ bool GlobalOpt::OptimizeGlobalVars(Module &M) {
     // Global variables without names cannot be referenced outside this module.
     if (!GV->hasName() && !GV->isDeclaration())
       GV->setLinkage(GlobalValue::InternalLinkage);
+    // Simplify the initializer.
+    if (GV->hasInitializer())
+      if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
+        TargetData *TD = getAnalysisIfAvailable<TargetData>();
+        Constant *New = ConstantFoldConstantExpression(CE, TD);
+        if (New && New != CE)
+          GV->setInitializer(New);
+      }
+    // Do more involved optimizations if the global is internal.
     if (!GV->isConstant() && GV->hasLocalLinkage() &&
         GV->hasInitializer())
       Changed |= ProcessInternalGlobal(GV, GVI);