[llvm-commits] [llvm] r119933 - /llvm/trunk/lib/Analysis/ConstantFolding.cpp

[Chris Lattner]

Author: lattner
Date: Sun Nov 21 02:39:01 2010
New Revision: 119933

URL: http://llvm.org/viewvc/llvm-project?rev=119933&view=rev
Log:
apply Dan's fix for PR8268 which allows constant folding to handle indexes over
zero sized elements.  This allows us to compile:

  #include <string>
  void foo() { std::string s; }

into an empty function.


Modified:
    llvm/trunk/lib/Analysis/ConstantFolding.cpp

Modified: llvm/trunk/lib/Analysis/ConstantFolding.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ConstantFolding.cpp?rev=119933&r1=119932&r2=119933&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ConstantFolding.cpp (original)
+++ llvm/trunk/lib/Analysis/ConstantFolding.cpp Sun Nov 21 02:39:01 2010
@@ -538,7 +538,7 @@
   for (unsigned i = 1; i != NumOps; ++i) {
     if ((i == 1 ||
          !isa<StructType>(GetElementPtrInst::getIndexedType(Ops[0]->getType(),
-                                                            reinterpret_cast<Value *const *>(Ops+1),
+                                        reinterpret_cast<Value *const *>(Ops+1),
                                                             i-1))) &&
         Ops[i]->getType() != IntPtrTy) {
       Any = true;
@@ -639,12 +639,19 @@
         
       // Determine which element of the array the offset points into.
       APInt ElemSize(BitWidth, TD->getTypeAllocSize(ATy->getElementType()));
+      const IntegerType *IntPtrTy = TD->getIntPtrType(Ty->getContext());
       if (ElemSize == 0)
-        return 0;
-      APInt NewIdx = Offset.udiv(ElemSize);
-      Offset -= NewIdx * ElemSize;
-      NewIdxs.push_back(ConstantInt::get(TD->getIntPtrType(Ty->getContext()),
-                                         NewIdx));
+        // The element size is 0. This may be [0 x Ty]*, so just use a zero
+        // index for this level and procede to the next level to see if it can
+        // accomodate the offset.
+        NewIdxs.push_back(ConstantInt::get(IntPtrTy, 0));
+      else {
+        // The element size is non-zero divide the offset by the element
+        // size (rounding down), to compute the index at this level.
+        APInt NewIdx = Offset.udiv(ElemSize);
+        Offset -= NewIdx * ElemSize;
+        NewIdxs.push_back(ConstantInt::get(IntPtrTy, NewIdx));
+      }
       Ty = ATy->getElementType();
     } else if (const StructType *STy = dyn_cast<StructType>(Ty)) {
       // Determine which field of the struct the offset points into. The
@@ -743,7 +750,8 @@
 Constant *llvm::ConstantFoldConstantExpression(const ConstantExpr *CE,
                                                const TargetData *TD) {
   SmallVector<Constant*, 8> Ops;
-  for (User::const_op_iterator i = CE->op_begin(), e = CE->op_end(); i != e; ++i) {
+  for (User::const_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))