[clang] [clang] Implement constexpr __builtin_bit_cast for complex types (PR #109981)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

Fixes https://github.com/llvm/llvm-project/issues/94620

---
Full diff: https://github.com/llvm/llvm-project/pull/109981.diff


2 Files Affected:

- (modified) clang/lib/AST/ExprConstant.cpp (+43) 
- (modified) clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp (+8) 


``````````diff
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 6387e375dda79c..86e956e6ea619a 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -7148,6 +7148,7 @@ class APValueToBufferConverter {
 
     case APValue::ComplexInt:
     case APValue::ComplexFloat:
+      return visitComplex(Val, Ty, Offset);
     case APValue::FixedPoint:
       // FIXME: We should support these.
 
@@ -7234,6 +7235,31 @@ class APValueToBufferConverter {
     return true;
   }
 
+  bool visitComplex(const APValue &Val, QualType Ty, CharUnits Offset) {
+    const ComplexType *ComplexTy = Ty->castAs<ComplexType>();
+    QualType EltTy = ComplexTy->getElementType();
+    CharUnits EltSizeChars = Info.Ctx.getTypeSizeInChars(EltTy);
+    bool IsInt = Val.isComplexInt();
+
+    if (IsInt) {
+      if (!visitInt(Val.getComplexIntReal(), EltTy,
+                    Offset + (0 * EltSizeChars)))
+        return false;
+      if (!visitInt(Val.getComplexIntImag(), EltTy,
+                    Offset + (1 * EltSizeChars)))
+        return false;
+    } else {
+      if (!visitFloat(Val.getComplexFloatReal(), EltTy,
+                      Offset + (0 * EltSizeChars)))
+        return false;
+      if (!visitFloat(Val.getComplexFloatImag(), EltTy,
+                      Offset + (1 * EltSizeChars)))
+        return false;
+    }
+
+    return true;
+  }
+
   bool visitVector(const APValue &Val, QualType Ty, CharUnits Offset) {
     const VectorType *VTy = Ty->castAs<VectorType>();
     QualType EltTy = VTy->getElementType();
@@ -7506,6 +7532,23 @@ class BufferToAPValueConverter {
     return ArrayValue;
   }
 
+  std::optional<APValue> visit(const ComplexType *Ty, CharUnits Offset) {
+    QualType ElementType = Ty->getElementType();
+    CharUnits ElementWidth = Info.Ctx.getTypeSizeInChars(ElementType);
+    bool IsInt = ElementType->isIntegerType();
+
+    std::optional<APValue> Values[2];
+    for (unsigned I = 0; I != 2; ++I) {
+      Values[I] = visitType(Ty->getElementType(), Offset + I * ElementWidth);
+      if (!Values[I])
+        return std::nullopt;
+    }
+
+    if (IsInt)
+      return APValue(Values[0]->getInt(), Values[1]->getInt());
+    return APValue(Values[0]->getFloat(), Values[1]->getFloat());
+  }
+
   std::optional<APValue> visit(const VectorType *VTy, CharUnits Offset) {
     QualType EltTy = VTy->getElementType();
     unsigned NElts = VTy->getNumElements();
diff --git a/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp b/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp
index 7520b43a194aba..5a35a8dfdbd9a4 100644
--- a/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp
+++ b/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp
@@ -511,3 +511,11 @@ constexpr bool9 bad_short_to_bool9 = __builtin_bit_cast(bool9, static_cast<unsig
 constexpr bool17 bad_int_to_bool17 = __builtin_bit_cast(bool17, 0x0001CAFEU);
 
 }
+
+namespace test_complex {
+  constexpr _Complex unsigned test_int_complex = { 0x0C05FEFE, 0xCAFEBABE };
+  static_assert(round_trip<_Complex unsigned>(0xCAFEBABE0C05FEFEULL), "");
+  static_assert(bit_cast<unsigned long long>(test_int_complex) == (LITTLE_END
+                                                                   ? 0xCAFEBABE0C05FEFE
+                                                                   : 0x0C05FEFECAFEBABE), "");
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/109981