[clang] [Clang] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - allow AVX/AVX512 subvector extraction intrinsics to be used in constexpr #157712 (PR #162836)

[Simon Pilgrim via cfe-commits]

================
@@ -11774,6 +11774,74 @@ bool VectorExprEvaluator::VisitCallExpr(const CallExpr *E) {
       return LHS.isSigned() ? LHS.ssub_sat(RHS) : LHS.usub_sat(RHS);
     });
 
+  case X86::BI__builtin_ia32_extract128i256:
+  case X86::BI__builtin_ia32_vextractf128_pd256:
+  case X86::BI__builtin_ia32_vextractf128_ps256:
+  case X86::BI__builtin_ia32_vextractf128_si256: {
+    APValue SourceVec, SourceImm;
+    if (!EvaluateAsRValue(Info, E->getArg(0), SourceVec) ||
+        !EvaluateAsRValue(Info, E->getArg(1), SourceImm))
+      return false;
+
+    if (!SourceVec.isVector())
+      return false;
+
+    const auto *RetVT = E->getType()->castAs<VectorType>();
+    unsigned RetLen = RetVT->getNumElements();
+    unsigned SrcLen = SourceVec.getVectorLength();
----------------
RKSimon wrote:

SrcLen unused variable

https://github.com/llvm/llvm-project/pull/162836