3 files changed, 39 insertions, 9 deletions
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index ebe8a27999f..677c3d92d02 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -78,20 +78,23 @@ Constant *FoldBitCast(Constant *C, Type *DestTy, const DataLayout &DL) {
       C = ConstantExpr::getBitCast(C, SrcIVTy);
     }
 
-    ConstantDataVector *CDV = dyn_cast<ConstantDataVector>(C);
-    if (!CDV)
-      return ConstantExpr::getBitCast(C, DestTy);
-
     // Now that we know that the input value is a vector of integers, just shift
     // and insert them into our result.
     unsigned BitShift = DL.getTypeAllocSizeInBits(SrcEltTy);
     APInt Result(IT->getBitWidth(), 0);
     for (unsigned i = 0; i != NumSrcElts; ++i) {
-      Result <<= BitShift;
+      Constant *Element;
       if (DL.isLittleEndian())
-        Result |= CDV->getElementAsInteger(NumSrcElts-i-1);
+        Element = C->getAggregateElement(NumSrcElts-i-1);
       else
-        Result |= CDV->getElementAsInteger(i);
+        Element = C->getAggregateElement(i);
+
+      auto *ElementCI = dyn_cast_or_null<ConstantInt>(Element);
+      if (!ElementCI)
+        return ConstantExpr::getBitCast(C, DestTy);
+
+      Result <<= BitShift;
+      Result |= ElementCI->getValue().zextOrSelf(IT->getBitWidth());
     }
 
     return ConstantInt::get(IT, Result);
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index a0a294db521..aca760810ef 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1405,8 +1405,7 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
     return;
   }
   // Handle a constant vector by taking the intersection of the known bits of
-  // each element.  There is no real need to handle ConstantVector here, because
-  // we don't handle undef in any particularly useful way.
+  // each element.
   if (ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(V)) {
     // We know that CDS must be a vector of integers. Take the intersection of
     // each element.
@@ -1420,6 +1419,26 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
     return;
   }
 
+  if (auto *CV = dyn_cast<ConstantVector>(V)) {
+    // We know that CV must be a vector of integers. Take the intersection of
+    // each element.
+    KnownZero.setAllBits(); KnownOne.setAllBits();
+    APInt Elt(KnownZero.getBitWidth(), 0);
+    for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) {
+      Constant *Element = CV->getAggregateElement(i);
+      auto *ElementCI = dyn_cast_or_null<ConstantInt>(Element);
+      if (!ElementCI) {
+        KnownZero.clearAllBits();
+        KnownOne.clearAllBits();
+        return;
+      }
+      Elt = ElementCI->getValue();
+      KnownZero &= ~Elt;
+      KnownOne &= Elt;
+    }
+    return;
+  }
+
   // Start out not knowing anything.
   KnownZero.clearAllBits(); KnownOne.clearAllBits();
 
diff --git a/llvm/test/Transforms/InstCombine/pr20678.ll b/llvm/test/Transforms/InstCombine/pr20678.ll
new file mode 100644
index 00000000000..4b5fac79449
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pr20678.ll
@@ -0,0 +1,8 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+define i1 @test1() {
+entry:
+  ret i1 icmp ne (i16 bitcast (<16 x i1> <i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 false, i1 false, i1 false, i1 false, i1 false, i1 false, i1 false, i1 false> to i16), i16 0)
+}
+; CHECK-LABEL: define i1 @test1(
+; CHECK:  ret i1 true