Revert "[VectorUtils] Query number of sign bits to allow more truncations"
This was a fairly simple patch but on closer inspection was seriously flawed and caused PR27690.
This reverts commit r268921.
llvm-svn: 269051
diff --git a/llvm/lib/Analysis/VectorUtils.cpp b/llvm/lib/Analysis/VectorUtils.cpp
index 2c03f1a..23a0de8 100644
--- a/llvm/lib/Analysis/VectorUtils.cpp
+++ b/llvm/lib/Analysis/VectorUtils.cpp
@@ -320,9 +320,6 @@
SmallPtrSet<Instruction *, 4> InstructionSet;
MapVector<Instruction *, uint64_t> MinBWs;
- assert(Blocks.size() > 0 && "Must have at least one block!");
- const DataLayout &DL = Blocks[0]->getModule()->getDataLayout();
-
// Determine the roots. We work bottom-up, from truncs or icmps.
bool SeenExtFromIllegalType = false;
for (auto *BB : Blocks)
@@ -366,19 +363,12 @@
// If we encounter a type that is larger than 64 bits, we can't represent
// it so bail out.
- APInt NeededBits = DB.getDemandedBits(I);
- unsigned BW = NeededBits.getBitWidth();
- if (BW > 64)
+ if (DB.getDemandedBits(I).getBitWidth() > 64)
return MapVector<Instruction *, uint64_t>();
- auto NSB = ComputeNumSignBits(I, DL);
-
- // Query demanded bits for the bits required by the instruction. Remove
- // any bits that are equal to the sign bit, because we can truncate the
- // instruction without changing their value.
- NeededBits &= APInt::getLowBitsSet(BW, BW - NSB);
- DBits[Leader] |= NeededBits.getZExtValue();
- DBits[I] |= NeededBits.getZExtValue();
+ uint64_t V = DB.getDemandedBits(I).getZExtValue();
+ DBits[Leader] |= V;
+ DBits[I] = V;
// Casts, loads and instructions outside of our range terminate a chain
// successfully.