[clang] [Clang] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - Allow AVX512 VPMULTISHIFTQB intrinsics to be used in constexpr (PR #168995)

[Simon Pilgrim via cfe-commits]

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@@ -13096,6 +13096,47 @@ bool VectorExprEvaluator::VisitCallExpr(const CallExpr *E) {
     return Success(R, E);
   }
 
+  case X86::BI__builtin_ia32_vpmultishiftqb128:
+  case X86::BI__builtin_ia32_vpmultishiftqb256:
+  case X86::BI__builtin_ia32_vpmultishiftqb512: {
+    assert(E->getNumArgs() == 2);
+
+    APValue A, B;
+    if (!Evaluate(A, Info, E->getArg(0)) || !Evaluate(B, Info, E->getArg(1)))
+      return false;
+
+    assert(A.getVectorLength() == B.getVectorLength());
+    unsigned NumBytesInQWord = 8;
+    unsigned NumBitsInByte = 8;
+    unsigned NumBytes = A.getVectorLength();
+    unsigned NumQWords = NumBytes / NumBytesInQWord;
+    SmallVector<APValue, 64> Result;
+    Result.reserve(NumBytes);
+
+    for (unsigned QWordId = 0; QWordId != NumQWords; ++QWordId) {
+      APInt BQWord(64, 0);
+      for (unsigned ByteIdx = 0; ByteIdx != NumBytesInQWord; ++ByteIdx) {
+        unsigned Idx = QWordId * NumBytesInQWord + ByteIdx;
+        uint64_t Byte = B.getVectorElt(Idx).getInt().getZExtValue();
+        BQWord.insertBits(APInt(8, Byte & 0xFF), ByteIdx * NumBitsInByte);
+      }
+
+      for (unsigned ByteIdx = 0; ByteIdx != NumBytesInQWord; ++ByteIdx) {
+        uint64_t Ctrl = A.getVectorElt(QWordId * NumBytesInQWord + ByteIdx)
----------------
RKSimon wrote:

Hoist `unsigned Idx = QWordId * NumBytesInQWord + ByteIdx;` - it should help with the clang-format line wrapping

https://github.com/llvm/llvm-project/pull/168995