[C2y] Remove support for _Imaginary (#97436)

WG14 N3274 removed _Imaginary from Annex G. Clang has never fully
supported Annex G or _Imaginary, so removal is pretty trivial for us.

Note, we are keeping _Imaginary as a keyword so that we get better
diagnostic behavior. This is still conforming because _I makes it a
reserved identifier, so it's not available for users to use as an
identifier anyway.

5 files changed, 12 insertions, 11 deletions

diff --git a/clang/lib/CodeGen/CGExprComplex.cpp b/clang/lib/CodeGen/CGExprComplex.cpp
index 84ad3b5..000d4ff 100644
--- a/clang/lib/CodeGen/CGExprComplex.cpp
+++ b/clang/lib/CodeGen/CGExprComplex.cpp
@@ -817,8 +817,6 @@ ComplexPairTy ComplexExprEmitter::EmitBinMul(const BinOpInfo &Op) {
     //
     // But we can fold away components which would be zero due to a real
     // operand according to C11 Annex G.5.1p2.
-    // FIXME: C11 also provides for imaginary types which would allow folding
-    // still more of this within the type system.
 
     CodeGenFunction::CGFPOptionsRAII FPOptsRAII(CGF, Op.FPFeatures);
     if (Op.LHS.second && Op.RHS.second) {
@@ -1049,9 +1047,6 @@ ComplexPairTy ComplexExprEmitter::EmitBinDiv(const BinOpInfo &Op) {
       // delegate to a libcall to handle all of the complexities and minimize
       // underflow/overflow cases. When FastMath is allowed we construct the
       // divide inline using the same algorithm as for integer operands.
-      //
-      // FIXME: We would be able to avoid the libcall in many places if we
-      // supported imaginary types in addition to complex types.
       BinOpInfo LibCallOp = Op;
       // If LHS was a real, supply a null imaginary part.
       if (!LHSi)
diff --git a/clang/lib/Sema/DeclSpec.cpp b/clang/lib/Sema/DeclSpec.cpp
index 96c90a60..9a4d52d 100644
--- a/clang/lib/Sema/DeclSpec.cpp
+++ b/clang/lib/Sema/DeclSpec.cpp
@@ -1146,7 +1146,7 @@ void DeclSpec::SaveWrittenBuiltinSpecs() {
 }
 
 /// Finish - This does final analysis of the declspec, rejecting things like
-/// "_Imaginary" (lacking an FP type). After calling this method, DeclSpec is
+/// "_Complex" (lacking an FP type). After calling this method, DeclSpec is
 /// guaranteed to be self-consistent, even if an error occurred.
 void DeclSpec::Finish(Sema &S, const PrintingPolicy &Policy) {
   // Before possibly changing their values, save specs as written.
@@ -1331,8 +1331,8 @@ void DeclSpec::Finish(Sema &S, const PrintingPolicy &Policy) {
     break;
   }
 
-  // TODO: if the implementation does not implement _Complex or _Imaginary,
-  // disallow their use.  Need information about the backend.
+  // TODO: if the implementation does not implement _Complex, disallow their
+  // use. Need information about the backend.
   if (TypeSpecComplex != TSC_unspecified) {
     if (TypeSpecType == TST_unspecified) {
       S.Diag(TSCLoc, diag::ext_plain_complex)
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
index 7ea760c..8fea7b0 100644
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -1805,7 +1805,8 @@ static void AddTypeSpecifierResults(const LangOptions &LangOpts,
   if (LangOpts.C99) {
     // C99-specific
     Results.AddResult(Result("_Complex", CCP_Type));
-    Results.AddResult(Result("_Imaginary", CCP_Type));
+    if (!LangOpts.C2y)
+      Results.AddResult(Result("_Imaginary", CCP_Type));
     Results.AddResult(Result("_Bool", CCP_Type));
     Results.AddResult(Result("restrict", CCP_Type));
   }
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index a4acf3b..7851c5d 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -4983,7 +4983,7 @@ static void AddKeywordsToConsumer(Sema &SemaRef,
     static const char *const CTypeSpecs[] = {
       "char", "const", "double", "enum", "float", "int", "long", "short",
       "signed", "struct", "union", "unsigned", "void", "volatile",
-      "_Complex", "_Imaginary",
+      "_Complex",
       // storage-specifiers as well
       "extern", "inline", "static", "typedef"
     };
@@ -4991,6 +4991,9 @@ static void AddKeywordsToConsumer(Sema &SemaRef,
     for (const auto *CTS : CTypeSpecs)
       Consumer.addKeywordResult(CTS);
 
+    if (SemaRef.getLangOpts().C99 && !SemaRef.getLangOpts().C2y)
+      Consumer.addKeywordResult("_Imaginary");
+
     if (SemaRef.getLangOpts().C99)
       Consumer.addKeywordResult("restrict");
     if (SemaRef.getLangOpts().Bool || SemaRef.getLangOpts().CPlusPlus)
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 066003c..f3510a0 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -1423,7 +1423,9 @@ static QualType ConvertDeclSpecToType(TypeProcessingState &state) {
     Result = Context.getVectorType(Result, 128/typeSize, VecKind);
   }
 
-  // FIXME: Imaginary.
+  // _Imaginary was a feature of C99 through C23 but was never supported in
+  // Clang. The feature was removed in C2y, but we retain the unsupported
+  // diagnostic for an improved user experience.
   if (DS.getTypeSpecComplex() == DeclSpec::TSC_imaginary)
     S.Diag(DS.getTypeSpecComplexLoc(), diag::err_imaginary_not_supported);