isBytewiseValue checks ConstantVector element by element

[vitalybuka]

Summary

Vector of the same value with few undefs will sill be considered "Bytewise"

[eugenis]

This seems correct. Any idea why it has not been done this way from the start?

[vitalybuka]

In D64031#1581498, @eugenis wrote:

This seems correct. Any idea why it has not been done this way from the start?

No

llvm/lib/Analysis/ValueTracking.cpp

Value *llvm::isBytewiseValue(Value *V, const DataLayout &DL) {
   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), DL))))
         return nullptr;
     return Val;
   }
 
-  if (isa<ConstantVector>(C)) {
-    Constant *Splat = cast<ConstantVector>(C)->getSplatValue();
-    return Splat ? isBytewiseValue(Splat, DL) : nullptr;
-  }
-
-  if (isa<ConstantArray>(C) || isa<ConstantStruct>(C)) {
+  if (isa<ConstantAggregate>(C)) {
     Value *Val = UndefInt8;
     for (unsigned I = 0, E = C->getNumOperands(); I != E; ++I)
       if (!(Val = Merge(Val, isBytewiseValue(C->getOperand(I), DL))))
         return nullptr;
     return Val;
   }
 
   // Don't try to handle the handful of other constants.

llvm/unittests/Analysis/ValueTrackingTest.cpp

const std::pair<const char *, const char *> IsBytewiseValueTests[] = {
         "i8 -1",
         "<5 x i64> <i64 -1, i64 -1, i64 -1, i64 -1, i64 -1>",
     },
     {
         "",
         "<4 x i8> <i8 1, i8 1, i8 2, i8 1>",
     },
     {
-        "",
+        "i8 5",
         "<2 x i8> < i8 5, i8 undef >",
     },
     {
         "i8 0",
         "[2 x [2 x i16]] zeroinitializer",
     },
     {
         "i8 undef",