[clang] [Headers][X86] Allow SLLDQ/SRLDQ byte shift intrinsics to be used in constexpr (PR #164166)

[Ye Tian via cfe-commits]

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@@ -3128,6 +3128,67 @@ static bool interp__builtin_ia32_vpconflict(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static bool interp__builtin_x86_pslldq_byteshift(InterpState &S, CodePtr OpPC,
+                                                 const CallExpr *Call,
+                                                 unsigned ID) {
+  assert(Call->getNumArgs() == 2);
+
+  APSInt ImmAPS = popToAPSInt(S, Call->getArg(1));
+  uint64_t Shift = ImmAPS.getZExtValue();
+
+  const Pointer &Src = S.Stk.pop<Pointer>();
+  if (!Src.getFieldDesc()->isPrimitiveArray())
+    return false;
+
+  unsigned NumElems = Src.getNumElems();
+  const Pointer &Dst = S.Stk.peek<Pointer>();
+  PrimType ElemT = Src.getFieldDesc()->getPrimType();
+
+  TYPE_SWITCH(ElemT, {
+    for (unsigned I = 0; I != NumElems; ++I) {
+      if (I < Shift) {
+        Dst.elem<T>(I) = T();
+      } else {
+        Dst.elem<T>(I) = Src.elem<T>(I - Shift);
+      }
+    }
+  });
+
+  Dst.initializeAllElements();
+
+  return true;
+}
+
+static bool interp__builtin_x86_psrldq_byteshift(InterpState &S, CodePtr OpPC,
+                                                 const CallExpr *Call,
+                                                 unsigned ID) {
+  assert(Call->getNumArgs() == 2);
+
+  APSInt ImmAPS = popToAPSInt(S, Call->getArg(1));
+  uint64_t Shift = ImmAPS.getZExtValue();
+
+  const Pointer &Src = S.Stk.pop<Pointer>();
+  if (!Src.getFieldDesc()->isPrimitiveArray())
+    return false;
+
+  unsigned NumElems = Src.getNumElems();
+  const Pointer &Dst = S.Stk.peek<Pointer>();
+  PrimType ElemT = Src.getFieldDesc()->getPrimType();
+
+  TYPE_SWITCH(ElemT, {
+    for (unsigned I = 0; I != NumElems; ++I) {
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TianYe717 wrote:

Done, thanks! I misunderstood this intrinsic.

https://github.com/llvm/llvm-project/pull/164166