Merge clang's isRepeatedBytePattern with LLVM's isBytewiseValue

Summary:
his code was in CGDecl.cpp and really belongs in LLVM's isBytewiseValue. Teach isBytewiseValue the tricks clang's isRepeatedBytePattern had, including merging undef properly, and recursing on more types.

clang part of this patch: D51752

Subscribers: dexonsmith, llvm-commits

Differential Revision: https://reviews.llvm.org/D51751

llvm-svn: 342709

1 files changed, 62 insertions, 32 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 122fa72d773..495324ff534 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3042,62 +3042,92 @@ bool llvm::isKnownNeverNaN(const Value *V, const TargetLibraryInfo *TLI,
   return true;
 }
 
-/// If the specified value can be set by repeating the same byte in memory,
-/// return the i8 value that it is represented with.  This is
-/// true for all i8 values obviously, but is also true for i32 0, i32 -1,
-/// i16 0xF0F0, double 0.0 etc.  If the value can't be handled with a repeated
-/// byte store (e.g. i16 0x1234), return null.
 Value *llvm::isBytewiseValue(Value *V) {
+
   // All byte-wide stores are splatable, even of arbitrary variables.
-  if (V->getType()->isIntegerTy(8)) return V;
+  if (V->getType()->isIntegerTy(8))
+    return V;
+
+  LLVMContext &Ctx = V->getContext();
+
+  // Undef don't care.
+  auto *UndefInt8 = UndefValue::get(Type::getInt8Ty(Ctx));
+  if (isa<UndefValue>(V))
+    return UndefInt8;
+
+  Constant *C = dyn_cast<Constant>(V);
+  if (!C) {
+    // Conceptually, we could handle things like:
+    //   %a = zext i8 %X to i16
+    //   %b = shl i16 %a, 8
+    //   %c = or i16 %a, %b
+    // but until there is an example that actually needs this, it doesn't seem
+    // worth worrying about.
+    return nullptr;
+  }
 
   // Handle 'null' ConstantArrayZero etc.
-  if (Constant *C = dyn_cast<Constant>(V))
-    if (C->isNullValue())
-      return Constant::getNullValue(Type::getInt8Ty(V->getContext()));
+  if (C->isNullValue())
+    return Constant::getNullValue(Type::getInt8Ty(Ctx));
 
-  // Constant float and double values can be handled as integer values if the
+  // Constant floating-point values can be handled as integer values if the
   // corresponding integer value is "byteable".  An important case is 0.0.
-  if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
-    if (CFP->getType()->isFloatTy())
-      V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(V->getContext()));
-    if (CFP->getType()->isDoubleTy())
-      V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(V->getContext()));
+  if (ConstantFP *CFP = dyn_cast<ConstantFP>(C)) {
+    Type *Ty = nullptr;
+    if (CFP->getType()->isHalfTy())
+      Ty = Type::getInt16Ty(Ctx);
+    else if (CFP->getType()->isFloatTy())
+      Ty = Type::getInt32Ty(Ctx);
+    else if (CFP->getType()->isDoubleTy())
+      Ty = Type::getInt64Ty(Ctx);
     // Don't handle long double formats, which have strange constraints.
+    return Ty ? isBytewiseValue(ConstantExpr::getBitCast(CFP, Ty)) : nullptr;
   }
 
   // We can handle constant integers that are multiple of 8 bits.
-  if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
+  if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) {
     if (CI->getBitWidth() % 8 == 0) {
       assert(CI->getBitWidth() > 8 && "8 bits should be handled above!");
-
       if (!CI->getValue().isSplat(8))
         return nullptr;
-      return ConstantInt::get(V->getContext(), CI->getValue().trunc(8));
+      return ConstantInt::get(Ctx, CI->getValue().trunc(8));
     }
   }
 
-  // A ConstantDataArray/Vector is splatable if all its members are equal and
-  // also splatable.
-  if (ConstantDataSequential *CA = dyn_cast<ConstantDataSequential>(V)) {
-    Value *Elt = CA->getElementAsConstant(0);
-    Value *Val = isBytewiseValue(Elt);
-    if (!Val)
+  auto Merge = [&](Value *LHS, Value *RHS) -> Value * {
+    if (LHS == RHS)
+      return LHS;
+    if (!LHS || !RHS)
       return nullptr;
+    if (LHS == UndefInt8)
+      return RHS;
+    if (RHS == UndefInt8)
+      return LHS;
+    return nullptr;
+  };
 
-    for (unsigned I = 1, E = CA->getNumElements(); I != E; ++I)
-      if (CA->getElementAsConstant(I) != Elt)
+  if (ConstantDataSequential *CA = dyn_cast<ConstantDataSequential>(C)) {
+    Value *Val = UndefInt8;
+    for (unsigned I = 0, E = CA->getNumElements(); I != E; ++I)
+      if (!(Val = Merge(Val, isBytewiseValue(CA->getElementAsConstant(I)))))
         return nullptr;
+    return Val;
+  }
+
+  if (isa<ConstantVector>(C)) {
+    Constant *Splat = cast<ConstantVector>(C)->getSplatValue();
+    return Splat ? isBytewiseValue(Splat) : nullptr;
+  }
 
+  if (isa<ConstantArray>(C) || isa<ConstantStruct>(C)) {
+    Value *Val = UndefInt8;
+    for (unsigned I = 0, E = C->getNumOperands(); I != E; ++I)
+      if (!(Val = Merge(Val, isBytewiseValue(C->getOperand(I)))))
+        return nullptr;
     return Val;
   }
 
-  // Conceptually, we could handle things like:
-  //   %a = zext i8 %X to i16
-  //   %b = shl i16 %a, 8
-  //   %c = or i16 %a, %b
-  // but until there is an example that actually needs this, it doesn't seem
-  // worth worrying about.
+  // Don't try to handle the handful of other constants.
   return nullptr;
 }