- Re-apply 52748 and friends with fix. GetConstantStringInfo() returns an empty string for ConstantAggregateZero case which surprises selectiondag.

- Correctly handle memcpy from constant string which is zero-initialized.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52891 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 3 insertions, 84 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index d45eb99d93..5d75489d14 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -9973,8 +9973,8 @@ static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI,
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(CI)) {
     // Instead of loading constant c string, use corresponding integer value
     // directly if string length is small enough.
-    const std::string &Str = CE->getOperand(0)->getStringValue();
-    if (!Str.empty()) {
+    std::string Str;
+    if (GetConstantStringInfo(CE->getOperand(0), Str) && !Str.empty()) {
       unsigned len = Str.length();
       const Type *Ty = cast<PointerType>(CE->getType())->getElementType();
       unsigned numBits = Ty->getPrimitiveSizeInBits();
diff --git a/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index 79ec3d941f..6bc6ad407f 100644
--- a/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -23,6 +23,7 @@
 #include "llvm/Module.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/IRBuilder.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/StringMap.h"
@@ -229,88 +230,6 @@ void LibCallOptimization::EmitFWrite(Value *Ptr, Value *Size, Value *File,
 // Helper Functions
 //===----------------------------------------------------------------------===//
 
-/// GetConstantStringInfo - This function computes the length of a
-/// null-terminated C string pointed to by V.  If successful, it returns true
-/// and returns the string in Str.  If unsuccessful, it returns false.
-static bool GetConstantStringInfo(Value *V, std::string &Str) {
-  // Look bitcast instructions.
-  if (BitCastInst *BCI = dyn_cast<BitCastInst>(V))
-    return GetConstantStringInfo(BCI->getOperand(0), Str);
-  
-  // If the value is not a GEP instruction nor a constant expression with a
-  // GEP instruction, then return false because ConstantArray can't occur
-  // any other way
-  User *GEP = 0;
-  if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) {
-    GEP = GEPI;
-  } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
-    if (CE->getOpcode() != Instruction::GetElementPtr)
-      return false;
-    GEP = CE;
-  } else {
-    return false;
-  }
-  
-  // Make sure the GEP has exactly three arguments.
-  if (GEP->getNumOperands() != 3)
-    return false;
-  
-  // Check to make sure that the first operand of the GEP is an integer and
-  // has value 0 so that we are sure we're indexing into the initializer.
-  if (ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(1))) {
-    if (!Idx->isZero())
-      return false;
-  } else
-    return false;
-  
-  // If the second index isn't a ConstantInt, then this is a variable index
-  // into the array.  If this occurs, we can't say anything meaningful about
-  // the string.
-  uint64_t StartIdx = 0;
-  if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
-    StartIdx = CI->getZExtValue();
-  else
-    return false;
-  
-  // The GEP instruction, constant or instruction, must reference a global
-  // variable that is a constant and is initialized. The referenced constant
-  // initializer is the array that we'll use for optimization.
-  GlobalVariable* GV = dyn_cast<GlobalVariable>(GEP->getOperand(0));
-  if (!GV || !GV->isConstant() || !GV->hasInitializer())
-    return false;
-  Constant *GlobalInit = GV->getInitializer();
-  
-  // Handle the ConstantAggregateZero case
-  if (isa<ConstantAggregateZero>(GlobalInit)) {
-    // This is a degenerate case. The initializer is constant zero so the
-    // length of the string must be zero.
-    Str.clear();
-    return true;
-  }
-  
-  // Must be a Constant Array
-  ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit);
-  if (Array == 0 || Array->getType()->getElementType() != Type::Int8Ty)
-    return false;
-  
-  // Get the number of elements in the array
-  uint64_t NumElts = Array->getType()->getNumElements();
-  
-  // Traverse the constant array from StartIdx (derived above) which is
-  // the place the GEP refers to in the array.
-  for (unsigned i = StartIdx; i < NumElts; ++i) {
-    Constant *Elt = Array->getOperand(i);
-    ConstantInt *CI = dyn_cast<ConstantInt>(Elt);
-    if (!CI) // This array isn't suitable, non-int initializer.
-      return false;
-    if (CI->isZero())
-      return true; // we found end of string, success!
-    Str += (char)CI->getZExtValue();
-  }
-  
-  return false; // The array isn't null terminated.
-}
-
 /// GetStringLengthH - If we can compute the length of the string pointed to by
 /// the specified pointer, return 'len+1'.  If we can't, return 0.
 static uint64_t GetStringLengthH(Value *V, SmallPtrSet<PHINode*, 32> &PHIs) {