Don't try to pull vector bitcasts that change the number of elements through

a select. A vector select is pairwise on each element so we'd need a new
condition with the right number of elements to select on. Fixes PR8994.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123963 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 28 insertions, 3 deletions

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index ab019a1362..2e908e73f9 100644
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -455,8 +455,9 @@ Value *InstCombiner::dyn_castFNegVal(Value *V) const {
 
 static Value *FoldOperationIntoSelectOperand(Instruction &I, Value *SO,
                                              InstCombiner *IC) {
-  if (CastInst *CI = dyn_cast<CastInst>(&I))
+  if (CastInst *CI = dyn_cast<CastInst>(&I)) {
     return IC->Builder->CreateCast(CI->getOpcode(), SO, I.getType());
+  }
 
   // Figure out if the constant is the left or the right argument.
   bool ConstIsRHS = isa<Constant>(I.getOperand(1));
@@ -498,11 +499,24 @@ Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) {
     // Bool selects with constant operands can be folded to logical ops.
     if (SI->getType()->isIntegerTy(1)) return 0;
 
+    // If it's a bitcast involving vectors, make sure it has the same number of
+    // elements on both sides.
+    if (BitCastInst *BC = dyn_cast<BitCastInst>(&Op)) {
+      const VectorType *DestTy = dyn_cast<VectorType>(BC->getDestTy());
+      const VectorType *SrcTy = dyn_cast<VectorType>(BC->getSrcTy());
+
+      // Verify that either both or neither are vectors.
+      if ((SrcTy == NULL) != (DestTy == NULL)) return 0;
+      // If vectors, verify that they have the same number of elements.
+      if (SrcTy && SrcTy->getNumElements() != DestTy->getNumElements())
+        return 0;
+    }
+    
     Value *SelectTrueVal = FoldOperationIntoSelectOperand(Op, TV, this);
     Value *SelectFalseVal = FoldOperationIntoSelectOperand(Op, FV, this);
 
-    return SelectInst::Create(SI->getCondition(), SelectTrueVal,
-                              SelectFalseVal);
+    return SelectInst::Create(SI->getCondition(),
+                              SelectTrueVal, SelectFalseVal);
   }
   return 0;
 }
diff --git a/test/Transforms/InstCombine/select.ll b/test/Transforms/InstCombine/select.ll
index 6633564c2b..54cfc467cc 100644
--- a/test/Transforms/InstCombine/select.ll
+++ b/test/Transforms/InstCombine/select.ll
@@ -689,3 +689,14 @@ define i64 @test50(i32 %a) nounwind {
 ; CHECK-NEXT: %min = select i1 %is_a_nonpositive, i64 %a_ext, i64 2
 ; CHECK-NEXT: ret i64 %min
 }
+
+; PR8994
+
+; Theis select instruction can't be eliminated because trying to do so would
+; change the number of vector elements. This used to assert.
+define i48 @test51(<3 x i1> %icmp, <3 x i16> %tmp) {
+  %select = select <3 x i1> %icmp, <3 x i16> zeroinitializer, <3 x i16> %tmp
+; CHECK: select <3 x i1>
+  %tmp2 = bitcast <3 x i16> %select to i48
+  ret i48 %tmp2
+}