[clang] [X86][Clang] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - allow AVX512 mask predicate intrinsics to be used in constexpr (PR #173739)

[Muhammad Abdul via cfe-commits]

================
@@ -12388,6 +12388,41 @@ bool VectorExprEvaluator::VisitCallExpr(const CallExpr *E) {
     return Success(APValue(ResultElements.data(), RetLen), E);
   }
 
+  case clang::X86::BI__builtin_ia32_cvtmask2b128:
+  case clang::X86::BI__builtin_ia32_cvtmask2b256:
+  case clang::X86::BI__builtin_ia32_cvtmask2b512:
+  case clang::X86::BI__builtin_ia32_cvtmask2w128:
+  case clang::X86::BI__builtin_ia32_cvtmask2w256:
+  case clang::X86::BI__builtin_ia32_cvtmask2w512:
+  case clang::X86::BI__builtin_ia32_cvtmask2d128:
+  case clang::X86::BI__builtin_ia32_cvtmask2d256:
+  case clang::X86::BI__builtin_ia32_cvtmask2d512:
+  case clang::X86::BI__builtin_ia32_cvtmask2q128:
+  case clang::X86::BI__builtin_ia32_cvtmask2q256:
+  case clang::X86::BI__builtin_ia32_cvtmask2q512: {
+    assert(E->getNumArgs() == 1);
+    APSInt Mask;
+    if (!EvaluateInteger(E->getArg(0), Mask, Info))
+      return false;
+
+    QualType VecTy = E->getType();
+    const VectorType *VT = VecTy->castAs<VectorType>();
+    unsigned VectorLen = VT->getNumElements();
+    QualType ElemTy = VT->getElementType();
+    unsigned ElemWidth = Info.Ctx.getTypeSize(ElemTy);
+
+    SmallVector<APValue, 16> Elems;
+    for (unsigned i = 0; i < VectorLen; ++i) {
----------------
0xzre wrote:

nit

```suggestion
    for (unsigned I = 0; I != VectorLen; ++I) {
```

https://github.com/llvm/llvm-project/pull/173739