[ConstantFolding] Fix bitcast vector of i1

[igorb]

Summary

[ConstantFolding] Fix bitcast vector of i1.
StoreSizeInBytes of i1 is 8,so current implementation return incorrect result.
For example: bitcast <8 x i1> <i1 true, i1 true, i1 false, i1 true, i1 false, i1 true, i1 false, i1 true> to i8
converted to i8 1

[majnemer]

LGTM

lib/Analysis/ConstantFolding.cpp

if (SrcEltTy->isFloatingPointTy()) {
       Type *SrcIVTy =
         VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumSrcElts);
       // Ask IR to do the conversion now that #elts line up.
       C = ConstantExpr::getBitCast(C, SrcIVTy);
     }
 
     // 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);
+    unsigned BitShift = DL.getTypeSizeInBits(SrcEltTy);
     APInt Result(IT->getBitWidth(), 0);
     for (unsigned i = 0; i != NumSrcElts; ++i) {
       Constant *Element;
       if (DL.isLittleEndian())
         Element = C->getAggregateElement(NumSrcElts-i-1);
       else
         Element = C->getAggregateElement(i);
 

test/Transforms/InstCombine/bitcast.ll

 define <2 x i64> @test7(<2 x i8*>* %arg) nounwind {
   %cast = bitcast <2 x i8*>* %arg to <2 x i64>*
   %load = load <2 x i64>, <2 x i64>* %cast, align 16
   ret <2 x i64> %load
 ; CHECK: @test7
 ; CHECK: bitcast
 ; CHECK: load
 }
+
+define i8 @test8() {
+  %res = bitcast <8 x i1> <i1 true, i1 true, i1 false, i1 true, i1 false, i1 true, i1 false, i1 true> to i8
+  ret i8 %res
+; CHECK: @test8
+; CHECK: ret i8 -85
+}