[InstCombine] Don't look through bitcast from vector in collectInsertionElements.

[craig.topper]

Summary

We're making a recursive call here and everything in the function
assumes we're looking at scalars. This would be violated if we
looked through a bitcast from vectors.

[craig.topper]

Remove FIXME from test case.

[spatel]

LGTM

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

static bool collectInsertionElements(Value *V, unsigned Shift,
 
   if (!V->hasOneUse()) return false;
 
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I) return false;
   switch (I->getOpcode()) {
   default: return false; // Unhandled case.
   case Instruction::BitCast:
+    if (I->getOperand(0)->getType()->isVectorTy())
+      return false;
     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
                                     isBigEndian);
   case Instruction::ZExt:
     if (!isMultipleOfTypeSize(
                           I->getOperand(0)->getType()->getPrimitiveSizeInBits(),
                               VecEltTy))
       return false;
     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,

llvm/test/Transforms/InstCombine/bitcast.ll

;
   %tmp23 = bitcast float %A to i32
   %tmp24 = zext i32 %tmp23 to i64
   %tmp25 = shl i64 %tmp24, 32
   %mask20 = or i64 %tmp25, 1109917696
   %tmp35 = bitcast i64 %mask20 to <2 x float>
   ret <2 x float> %tmp35
 }
 
-; FIXME: This test should not be optimized by OptimizeIntegerToVectorInsertions.
-; The bitcast from vector is confusing it.
+; This test should not be optimized by OptimizeIntegerToVectorInsertions.
+; The bitcast from vector previously confused it.
 define <2 x i64> @int2vec_insertion_bitcast_from_vec(i64 %x) {
 ; CHECK-LABEL: @int2vec_insertion_bitcast_from_vec(
-; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <2 x i64> <i64 poison, i64 0>, i64 [[X:%.*]], i64 0
-; CHECK-NEXT:    ret <2 x i64> [[TMP1]]
+; CHECK-NEXT:    [[A:%.*]] = bitcast i64 [[X:%.*]] to <8 x i8>
+; CHECK-NEXT:    [[B:%.*]] = zext <8 x i8> [[A]] to <8 x i16>
+; CHECK-NEXT:    [[D:%.*]] = bitcast <8 x i16> [[B]] to <2 x i64>
+; CHECK-NEXT:    ret <2 x i64> [[D]]
 ;
   %a = bitcast i64 %x to <8 x i8>
   %b = zext <8 x i8> %a to <8 x i16>
   %c = bitcast <8 x i16> %b to i128
   %d = bitcast i128 %c to <2 x i64>
   ret <2 x i64> %d
 }