[clang][bytecode] Fix vector shifts on big-endian systems (#109800)

For shifts, the LHS and RHS element types might be different. The
variable naming here could probably use some love now, but I'm trying to
fix this as fast as possible.

See the discussion in #108949

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -1282,9 +1282,8 @@ bool Compiler<Emitter>::VisitVectorBinOp(const BinaryOperator *E) {
                 ? BinaryOperator::getOpForCompoundAssignment(E->getOpcode())
                 : E->getOpcode();
 
-  // The LHS and RHS of a comparison operator must have the same type. So we
-  // just use LHS vector element type here.
   PrimType ElemT = this->classifyVectorElementType(LHS->getType());
+  PrimType RHSElemT = this->classifyVectorElementType(RHS->getType());
   PrimType ResultElemT = this->classifyVectorElementType(E->getType());
 
   // Evaluate LHS and save value to LHSOffset.
@@ -1312,7 +1311,7 @@ bool Compiler<Emitter>::VisitVectorBinOp(const BinaryOperator *E) {
   PrimType PromotT = classifyPrim(PromotTy);
   PrimType OpT = NeedIntPromot ? PromotT : ElemT;
 
-  auto getElem = [=](unsigned Offset, unsigned Index) {
+  auto getElem = [=](unsigned Offset, PrimType ElemT, unsigned Index) {
     if (!this->emitGetLocal(PT_Ptr, Offset, E))
       return false;
     if (!this->emitArrayElemPop(ElemT, Index, E))
@@ -1342,9 +1341,9 @@ bool Compiler<Emitter>::VisitVectorBinOp(const BinaryOperator *E) {
   }
 
   for (unsigned I = 0; I != VecTy->getNumElements(); ++I) {
-    if (!getElem(LHSOffset, I))
+    if (!getElem(LHSOffset, ElemT, I))
       return false;
-    if (!getElem(RHSOffset, I))
+    if (!getElem(RHSOffset, RHSElemT, I))
       return false;
     switch (Op) {
     case BO_Add:
@@ -1372,11 +1371,11 @@ bool Compiler<Emitter>::VisitVectorBinOp(const BinaryOperator *E) {
         return false;
       break;
     case BO_Shl:
-      if (!this->emitShl(OpT, ElemT, E))
+      if (!this->emitShl(OpT, RHSElemT, E))
         return false;
       break;
     case BO_Shr:
-      if (!this->emitShr(OpT, ElemT, E))
+      if (!this->emitShr(OpT, RHSElemT, E))
         return false;
       break;
     case BO_EQ: