[llvm] c5a1d0a - Revert "[ConstantFold] Remove unnecessary BitCastConstantVector() (NFCI)"

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-11-03T11:25:41+01:00
New Revision: c5a1d0ae6a69c7ba39a4386c30e49da0d2a3664e

URL: https://github.com/llvm/llvm-project/commit/c5a1d0ae6a69c7ba39a4386c30e49da0d2a3664e
DIFF: https://github.com/llvm/llvm-project/commit/c5a1d0ae6a69c7ba39a4386c30e49da0d2a3664e.diff

LOG: Revert "[ConstantFold] Remove unnecessary BitCastConstantVector() (NFCI)"

This reverts commit 2182561b7ba675ca87356c02474eecb6ecfaa23f.

The all-ones special case in this case isn't redundant. Will redo
the change while preserving it.

Added: 
    

Modified: 
    llvm/lib/IR/ConstantFold.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index d69665bd6c56ae6..a263cdcf4008a2a 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -37,6 +37,45 @@ using namespace llvm::PatternMatch;
 //                ConstantFold*Instruction Implementations
 //===----------------------------------------------------------------------===//
 
+/// Convert the specified vector Constant node to the specified vector type.
+/// At this point, we know that the elements of the input vector constant are
+/// all simple integer or FP values.
+static Constant *BitCastConstantVector(Constant *CV, VectorType *DstTy) {
+
+  if (CV->isAllOnesValue()) return Constant::getAllOnesValue(DstTy);
+  if (CV->isNullValue()) return Constant::getNullValue(DstTy);
+
+  // Do not iterate on scalable vector. The num of elements is unknown at
+  // compile-time.
+  if (isa<ScalableVectorType>(DstTy))
+    return nullptr;
+
+  // If this cast changes element count then we can't handle it here:
+  // doing so requires endianness information.  This should be handled by
+  // Analysis/ConstantFolding.cpp
+  unsigned NumElts = cast<FixedVectorType>(DstTy)->getNumElements();
+  if (NumElts != cast<FixedVectorType>(CV->getType())->getNumElements())
+    return nullptr;
+
+  Type *DstEltTy = DstTy->getElementType();
+  // Fast path for splatted constants.
+  if (Constant *Splat = CV->getSplatValue()) {
+    return ConstantVector::getSplat(DstTy->getElementCount(),
+                                    ConstantExpr::getBitCast(Splat, DstEltTy));
+  }
+
+  SmallVector<Constant*, 16> Result;
+  Type *Ty = IntegerType::get(CV->getContext(), 32);
+  for (unsigned i = 0; i != NumElts; ++i) {
+    Constant *C =
+      ConstantExpr::getExtractElement(CV, ConstantInt::get(Ty, i));
+    C = ConstantExpr::getBitCast(C, DstEltTy);
+    Result.push_back(C);
+  }
+
+  return ConstantVector::get(Result);
+}
+
 /// This function determines which opcode to use to fold two constant cast
 /// expressions together. It uses CastInst::isEliminableCastPair to determine
 /// the opcode. Consequently its just a wrapper around that function.
@@ -75,12 +114,24 @@ static Constant *FoldBitCast(Constant *V, Type *DestTy) {
   // Handle casts from one vector constant to another.  We know that the src
   // and dest type have the same size (otherwise its an illegal cast).
   if (VectorType *DestPTy = dyn_cast<VectorType>(DestTy)) {
+    if (VectorType *SrcTy = dyn_cast<VectorType>(V->getType())) {
+      assert(DestPTy->getPrimitiveSizeInBits() ==
+                 SrcTy->getPrimitiveSizeInBits() &&
+             "Not cast between same sized vectors!");
+      SrcTy = nullptr;
+      // First, check for null.  Undef is already handled.
+      if (isa<ConstantAggregateZero>(V))
+        return Constant::getNullValue(DestTy);
+
+      // Handle ConstantVector and ConstantAggregateVector.
+      return BitCastConstantVector(V, DestPTy);
+    }
+
     // Canonicalize scalar-to-vector bitcasts into vector-to-vector bitcasts
     // This allows for other simplifications (although some of them
     // can only be handled by Analysis/ConstantFolding.cpp).
     if (isa<ConstantInt>(V) || isa<ConstantFP>(V))
       return ConstantExpr::getBitCast(ConstantVector::get(V), DestPTy);
-    return nullptr;
   }
 
   // Handle integral constant input.