[clang] [CLANG] Full support of complex multiplication and division. (PR #81514)

Thu Feb 22 06:56:09 PST 2024

llvmbot wrote:



@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang-driver

Author: Zahira Ammarguellat (zahiraam)

<details>
<summary>Changes</summary>

In clang there are two options `-f[no]cx-limited-range` and `-f[no]cx-fortran-rules` that control the range of complex multiplication and division. However, it is unclear how these options interact with one another. For instance, what should happen when the users compile with `-fcx-fortran-rules -fno-cx-limited-range` or `-fcx-limited-range -fno-cx-fortran-rules`? 

In this patch we are introducing a new option to solve the issue and give a greater flexibility to the user to control the behavior of the compiler when performing multiplication and division of complex floating-point values. This new option will **replace** the two options above.

`-fcomplex-arihmetic=[full|improved|promoted|basic]`

`full`: Implementation of complex division and multiplication using a call to runtime library functions (generally the case, but the BE might sometimes replace the library call if it knows enough about the potential range of the inputs). Overflow and non-finite values are handled by the library implementation.

`improved`: Implementation of complex division using the Smith algorithm at source precision. Smith's algorithm for complex division. See SMITH, R. L. Algorithm 116: Complex division. Commun. ACM 5, 8 (1962). This value offers improved handling for overflow in intermediate calculations, but overflow may occur. NaN and infinite and values are not handled in some     cases.

`promoted`: Implementation of complex division using algebraic formulas at higher precision. Overflow is handled. Non-finite values are handled in some cases. If the target hardware does not have native support for a higher precision data type, an implementation for the complex operation will be used to provide improved guards against intermediate overflow, but overflow and underflow may still occur in some cases. NaN and infinite and values are not handled. This is the default value.

`basic`: Implementation of complex division and multiplication using algebraic formulas at source precision. No special handling to avoid overflow. NaN and infinite and values are not handled.

`fcx-limited-range` will alias `-fcomplex-arithmetic=basic`
`-fcx-fortran-rules` will alias `-fcomplex-arithmetic=improved`
`-fno-cx-limited-range` and `-fno-cx-fortran-rules` will alias `-fcomplex-arithmetic=full`

The complex division and multiplication will be implemented as follows depending on the option used.

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-fcomplex-arithmetic | div | mul
-- | -- | --
basic | algebraic form | algebraic form
improved | smith's algorithm | algebraic form
full | libcall | libcall + nan processing
promoted | algebraic form + higher precision | algebraic form




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---

Patch is 54.92 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/81514.diff


12 Files Affected:

- (modified) clang/docs/UsersManual.rst (+28-13) 
- (modified) clang/include/clang/Basic/DiagnosticDriverKinds.td (+2) 
- (modified) clang/include/clang/Basic/LangOptions.h (+32-1) 
- (modified) clang/include/clang/Driver/Options.td (+6-19) 
- (modified) clang/lib/CodeGen/CGExprComplex.cpp (+57-8) 
- (modified) clang/lib/Driver/ToolChains/Clang.cpp (+48-50) 
- (modified) clang/lib/Parse/ParsePragma.cpp (+3-3) 
- (modified) clang/test/CodeGen/complex-math.c (+1-1) 
- (modified) clang/test/CodeGen/cx-complex-range.c (+151-96) 
- (modified) clang/test/CodeGen/pragma-cx-limited-range.c (+179-44) 
- (modified) clang/test/CodeGen/smiths-complex-div.c (+52-52) 
- (modified) clang/test/Driver/range.c (+76-35) 


``````````diff

diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index 7391e4cf3a9aeb..ca011ce05b1525 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -1847,19 +1847,34 @@ floating point semantic models: precise (the default), strict, and fast.
    * ``16`` - Forces ``_Float16`` operations to be emitted without using excess
      precision arithmetic.
 
-.. option:: -fcx-limited-range:
-
-   This option enables the naive mathematical formulas for complex division and
-   multiplication with no NaN checking of results. The default is
-   ``-fno-cx-limited-range``, but this option is enabled by the ``-ffast-math``
-   option.
-
-.. option:: -fcx-fortran-rules:
-
-   This option enables the naive mathematical formulas for complex
-   multiplication and enables application of Smith's algorithm for complex
-   division. See SMITH, R. L. Algorithm 116: Complex division. Commun.
-   ACM 5, 8 (1962). The default is ``-fno-cx-fortran-rules``.
+.. option:: -fcomplex-arithmetic=<value>:
+
+   This option specifies the implementation for complex multiplication and division.
+
+   Valid values are: ``basic``, ``improved``, ``full`` and ``promoted``.
+
+   * ``basic`` Implementation of complex division and multiplication using
+     algebraic formulas at source precision. No special handling to avoid
+     overflow. NaN and infinite and  values are not handled.
+   * ``improved`` Implementation of complex division using the Smith algorithm
+     at source precision. Smith's algorithm for complex division.
+     See SMITH, R. L. Algorithm 116: Complex division. Commun. ACM 5, 8 (1962).
+     This value offers improved handling for overflow in intermediate
+     calculations, but overflow may occur. NaN and infinite and  values are not
+     handled in some cases.
+   * ``full`` Implementation of complex division and multiplication using a
+     call to runtime library functions (generally the case, but the BE might
+     sometimes replace the library call if it knows enough about the potential
+     range of the inputs). Overflow and non-finite values are handled by the
+     library implementation. For the case of multiplication overflow will occur in
+     accordance with normal floating-point rules.
+   * ``promoted`` Implementation of complex division using algebraic formulas at
+     higher precision. Overflow is handled. Non-finite values are handled in some
+     cases. If the target does not have native support for a higher precision
+     data type, an implementation for the complex operation will be used to provide
+     improved guards against intermediate overflow, but overflow and underflow may
+     still occur in some cases. NaN and infinite and  values are not handled.
+     This is the default value.
 
 .. _floating-point-environment:
 
diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
index b13181f6e70894..b904a5f54238c7 100644
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -445,6 +445,8 @@ def warn_drv_no_floating_point_registers: Warning<
   InGroup<UnsupportedABI>;
 def warn_ignoring_ftabstop_value : Warning<
   "ignoring invalid -ftabstop value '%0', using default value %1">;
+def warn_nnan_ninf_with_full_range_complex_arithmetic : Warning<
+  "use of nnan or ninf flags in the presence of '%0' option">;
 def warn_drv_overriding_option : Warning<
   "overriding '%0' option with '%1'">,
   InGroup<DiagGroup<"overriding-option">>;
diff --git a/clang/include/clang/Basic/LangOptions.h b/clang/include/clang/Basic/LangOptions.h
index 862952d336ef31..2de21c5f60316b 100644
--- a/clang/include/clang/Basic/LangOptions.h
+++ b/clang/include/clang/Basic/LangOptions.h
@@ -396,7 +396,38 @@ class LangOptionsBase {
     IncompleteOnly = 3,
   };
 
-  enum ComplexRangeKind { CX_Full, CX_Limited, CX_Fortran, CX_None };
+  /// Controls the various implementations for complex multiplication and
+  // division.
+  enum ComplexRangeKind {
+    /// Implementation of complex division and multiplication using a call to
+    ///  runtime library functions(generally the case, but the BE might
+    /// sometimes replace the library call if it knows enough about the
+    /// potential range of the inputs). Overflow and non -finite values are
+    /// handled by the library implementation.
+    CX_Full,
+
+    /// Implementation of complex division offering an improved handling
+    /// for overflow in intermediate calculations with no special handling for
+    /// NaN and infinite and values.
+    CX_Improved,
+
+    /// Implementation of complex division using algebraic formulas at
+    /// higher precision. Overflow is handled. Non-finite values are handled in
+    /// some cases. If the target hardware does not have native support for a
+    /// higher precision data type, an implementation for the complex operation
+    /// will be used to provide improved guards against intermediate overflow,
+    /// but overflow and underflow may still occur in some cases. NaN and
+    /// infinite and  values are not handled. This is the default value.
+    CX_Promoted,
+
+    /// Implementation of complex division and multiplication using
+    /// algebraic formulas at source precision. No special handling to avoid
+    /// overflow.NaN and infinite and values are not handled.
+    CX_Basic,
+
+    /// No range rule is enabled.
+    CX_None
+  };
 
   // Define simple language options (with no accessors).
 #define LANGOPT(Name, Bits, Default, Description) unsigned Name : Bits;
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 3a028fadb25b18..3757317a84f8fe 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1039,28 +1039,15 @@ defm offload_uniform_block : BoolFOption<"offload-uniform-block",
   NegFlag<SetFalse, [], [ClangOption, CC1Option], "Don't assume">,
   BothFlags<[], [ClangOption], " that kernels are launched with uniform block sizes (default true for CUDA/HIP and false otherwise)">>;
 
-def fcx_limited_range : Joined<["-"], "fcx-limited-range">,
-  Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
-  HelpText<"Basic algebraic expansions of complex arithmetic operations "
-           "involving are enabled.">;
-
-def fno_cx_limited_range : Joined<["-"], "fno-cx-limited-range">,
-  Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
-  HelpText<"Basic algebraic expansions of complex arithmetic operations "
-           "involving are disabled.">;
-
-def fcx_fortran_rules : Joined<["-"], "fcx-fortran-rules">,
-  Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
-  HelpText<"Range reduction is enabled for complex arithmetic operations.">;
-
-def fno_cx_fortran_rules : Joined<["-"], "fno-cx-fortran-rules">,
-  Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
-  HelpText<"Range reduction is disabled for complex arithmetic operations.">;
+def fcomplex_arithmetic_EQ : Joined<["-"], "fcomplex-arithmetic=">, Group<f_Group>,
+  Visibility<[ClangOption, CC1Option]>,
+  Values<"full,improved,promoted,basic">, NormalizedValuesScope<"LangOptions">,
+  NormalizedValues<["CX_Full", "CX_Improved", "CX_Promoted", "CX_Basic"]>;
 
 def complex_range_EQ : Joined<["-"], "complex-range=">, Group<f_Group>,
   Visibility<[CC1Option]>,
-  Values<"full,limited,fortran">, NormalizedValuesScope<"LangOptions">,
-  NormalizedValues<["CX_Full", "CX_Limited", "CX_Fortran"]>,
+  Values<"full,improved,promoted,basic">, NormalizedValuesScope<"LangOptions">,
+  NormalizedValues<["CX_Full", "CX_Improved", "CX_Promoted", "CX_Basic"]>,
   MarshallingInfoEnum<LangOpts<"ComplexRange">, "CX_Full">;
 
 // OpenCL-only Options
diff --git a/clang/lib/CodeGen/CGExprComplex.cpp b/clang/lib/CodeGen/CGExprComplex.cpp
index 176a7e00141f94..9111488f50bcf4 100644
--- a/clang/lib/CodeGen/CGExprComplex.cpp
+++ b/clang/lib/CodeGen/CGExprComplex.cpp
@@ -283,9 +283,48 @@ class ComplexExprEmitter
   ComplexPairTy EmitComplexBinOpLibCall(StringRef LibCallName,
                                         const BinOpInfo &Op);
 
-  QualType getPromotionType(QualType Ty) {
+  QualType HigherPrecisionTypeForComplexArithmetic(QualType ElementType,
+                                                   bool IsDivOpCode) {
+    const TargetInfo &TI = CGF.getContext().getTargetInfo();
+    if (const auto *BT = dyn_cast<BuiltinType>(ElementType)) {
+      switch (BT->getKind()) {
+      case BuiltinType::Kind::Float16:
+      case BuiltinType::Kind::BFloat16: {
+        return CGF.getContext().getComplexType(CGF.getContext().FloatTy);
+      }
+      case BuiltinType::Kind::Float:
+        return CGF.getContext().getComplexType(CGF.getContext().DoubleTy);
+      case BuiltinType::Kind::Double:
+        if (TI.hasLongDoubleType()) {
+          return CGF.getContext().getComplexType(CGF.getContext().LongDoubleTy);
+        } else {
+          return QualType();
+        }
+      case BuiltinType::Kind::LongDouble:
+        if (TI.getTriple().isOSLinux()) {
+          if (TI.hasFloat128Type() && !TI.hasLongDoubleType())
+            return CGF.getContext().getComplexType(CGF.getContext().Float128Ty);
+          else
+            return CGF.getContext().getComplexType(
+                CGF.getContext().LongDoubleTy);
+        }
+        if (TI.getTriple().isOSWindows())
+          return CGF.getContext().getComplexType(CGF.getContext().LongDoubleTy);
+      default:
+        return QualType();
+      }
+    }
+    return QualType();
+  }
+
+  QualType getPromotionType(QualType Ty, bool IsDivOpCode = false) {
     if (auto *CT = Ty->getAs<ComplexType>()) {
       QualType ElementType = CT->getElementType();
+      if (IsDivOpCode && ElementType->isFloatingType() &&
+          CGF.getLangOpts().getComplexRange() ==
+              LangOptions::ComplexRangeKind::CX_Promoted)
+        return HigherPrecisionTypeForComplexArithmetic(ElementType,
+                                                       IsDivOpCode);
       if (ElementType.UseExcessPrecision(CGF.getContext()))
         return CGF.getContext().getComplexType(CGF.getContext().FloatTy);
     }
@@ -296,11 +335,12 @@ class ComplexExprEmitter
 
 #define HANDLEBINOP(OP)                                                        \
   ComplexPairTy VisitBin##OP(const BinaryOperator *E) {                        \
-    QualType promotionTy = getPromotionType(E->getType());                     \
+    QualType promotionTy = getPromotionType(                                   \
+        E->getType(),                                                          \
+        (E->getOpcode() == BinaryOperatorKind::BO_Div) ? true : false);        \
     ComplexPairTy result = EmitBin##OP(EmitBinOps(E, promotionTy));            \
     if (!promotionTy.isNull())                                                 \
-      result =                                                                 \
-          CGF.EmitUnPromotedValue(result, E->getType());                       \
+      result = CGF.EmitUnPromotedValue(result, E->getType());                  \
     return result;                                                             \
   }
 
@@ -790,8 +830,10 @@ ComplexPairTy ComplexExprEmitter::EmitBinMul(const BinOpInfo &Op) {
       ResR = Builder.CreateFSub(AC, BD, "mul_r");
       ResI = Builder.CreateFAdd(AD, BC, "mul_i");
 
-      if (Op.FPFeatures.getComplexRange() == LangOptions::CX_Limited ||
-          Op.FPFeatures.getComplexRange() == LangOptions::CX_Fortran)
+      if (Op.FPFeatures.getComplexRange() == LangOptions::CX_Basic ||
+          Op.FPFeatures.getComplexRange() == LangOptions::CX_Improved ||
+          Op.FPFeatures.getComplexRange() == LangOptions::CX_Promoted ||
+          CGF.getLangOpts().NoHonorInfs || CGF.getLangOpts().NoHonorNaNs)
         return ComplexPairTy(ResR, ResI);
 
       // Emit the test for the real part becoming NaN and create a branch to
@@ -982,9 +1024,16 @@ ComplexPairTy ComplexExprEmitter::EmitBinDiv(const BinOpInfo &Op) {
     llvm::Value *OrigLHSi = LHSi;
     if (!LHSi)
       LHSi = llvm::Constant::getNullValue(RHSi->getType());
-    if (Op.FPFeatures.getComplexRange() == LangOptions::CX_Fortran)
+    const TargetInfo &TI = CGF.getContext().getTargetInfo();
+    QualType ComplexElementTy =
+        Op.Ty->castAs<ComplexType>()->getElementType();
+    const BuiltinType *BT = ComplexElementTy->getAs<BuiltinType>();
+    if (Op.FPFeatures.getComplexRange() == LangOptions::CX_Improved ||
+        (TI.getTriple().isOSLinux() &&
+         BT->getKind() == BuiltinType::Kind::LongDouble))
       return EmitRangeReductionDiv(LHSr, LHSi, RHSr, RHSi);
-    else if (Op.FPFeatures.getComplexRange() == LangOptions::CX_Limited)
+    else if (Op.FPFeatures.getComplexRange() == LangOptions::CX_Basic ||
+             Op.FPFeatures.getComplexRange() == LangOptions::CX_Promoted)
       return EmitAlgebraicDiv(LHSr, LHSi, RHSr, RHSi);
     else if (!CGF.getLangOpts().FastMath ||
              // '-ffast-math' is used in the command line but followed by an
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 7c0409f0c3097a..c03000347d8d6e 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2687,45 +2687,42 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
   }
 }
 
-static StringRef EnumComplexRangeToStr(LangOptions::ComplexRangeKind Range) {
-  StringRef RangeStr = "";
+static std::string ComplexRangeKindToStr(LangOptions::ComplexRangeKind Range) {
   switch (Range) {
-  case LangOptions::ComplexRangeKind::CX_Limited:
-    return "-fcx-limited-range";
+  case LangOptions::ComplexRangeKind::CX_Full:
+    return "full";
     break;
-  case LangOptions::ComplexRangeKind::CX_Fortran:
-    return "-fcx-fortran-rules";
+  case LangOptions::ComplexRangeKind::CX_Basic:
+    return "basic";
     break;
-  default:
-    return RangeStr;
+  case LangOptions::ComplexRangeKind::CX_Improved:
+    return "improved";
+    break;
+  case LangOptions::ComplexRangeKind::CX_Promoted:
+    return "promoted";
     break;
+  default:
+    return "";
   }
 }
 
+static std::string ComplexArithmeticStr(LangOptions::ComplexRangeKind Range) {
+  return "-fcomplex-arithmetic=" + ComplexRangeKindToStr(Range);
+}
+
 static void EmitComplexRangeDiag(const Driver &D,
                                  LangOptions::ComplexRangeKind Range1,
                                  LangOptions::ComplexRangeKind Range2) {
   if (Range1 != Range2 && Range1 != LangOptions::ComplexRangeKind::CX_None)
     D.Diag(clang::diag::warn_drv_overriding_option)
-        << EnumComplexRangeToStr(Range1) << EnumComplexRangeToStr(Range2);
+        << ComplexArithmeticStr(Range1) << ComplexArithmeticStr(Range2);
 }
 
 static std::string
 RenderComplexRangeOption(LangOptions::ComplexRangeKind Range) {
-  std::string ComplexRangeStr = "-complex-range=";
-  switch (Range) {
-  case LangOptions::ComplexRangeKind::CX_Full:
-    ComplexRangeStr += "full";
-    break;
-  case LangOptions::ComplexRangeKind::CX_Limited:
-    ComplexRangeStr += "limited";
-    break;
-  case LangOptions::ComplexRangeKind::CX_Fortran:
-    ComplexRangeStr += "fortran";
-    break;
-  default:
-    assert(0 && "Unexpected range option");
-  }
+  std::string ComplexRangeStr = ComplexRangeKindToStr(Range);
+  if (!ComplexRangeStr.empty())
+    return "-complex-range=" + ComplexRangeStr;
   return ComplexRangeStr;
 }
 
@@ -2792,9 +2789,14 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
     FPExceptionBehavior = "";
     // If fast-math is set then set the fp-contract mode to fast.
     FPContract = "fast";
-    // ffast-math enables limited range rules for complex multiplication and
+    // ffast-math enables basic range rules for complex multiplication and
     // division.
-    Range = LangOptions::ComplexRangeKind::CX_Limited;
+    // Warn if user expects to perform full implementation of complex
+    // multiplication or division in the presence of nnan or ninf flags.
+    if (Range == LangOptions::ComplexRangeKind::CX_Full)
+      D.Diag(clang::diag::warn_nnan_ninf_with_full_range_complex_arithmetic)
+          << ComplexArithmeticStr(Range);
+    Range = LangOptions::ComplexRangeKind::CX_Basic;
     SeenUnsafeMathModeOption = true;
   };
 
@@ -2809,24 +2811,24 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
     switch (optID) {
     default:
       break;
-    case options::OPT_fcx_limited_range: {
-      EmitComplexRangeDiag(D, Range, LangOptions::ComplexRangeKind::CX_Limited);
-      Range = LangOptions::ComplexRangeKind::CX_Limited;
-      break;
-    }
-    case options::OPT_fno_cx_limited_range:
-      EmitComplexRangeDiag(D, Range, LangOptions::ComplexRangeKind::CX_Full);
-      Range = LangOptions::ComplexRangeKind::CX_Full;
-      break;
-    case options::OPT_fcx_fortran_rules: {
-      EmitComplexRangeDiag(D, Range, LangOptions::ComplexRangeKind::CX_Fortran);
-      Range = LangOptions::ComplexRangeKind::CX_Fortran;
+    case options::OPT_fcomplex_arithmetic_EQ: {
+      LangOptions::ComplexRangeKind RangeVal;
+      StringRef Val = A->getValue();
+      if (Val.equals("full"))
+        RangeVal = LangOptions::ComplexRangeKind::CX_Full;
+      else if (Val.equals("improved"))
+        RangeVal = LangOptions::ComplexRangeKind::CX_Improved;
+      else if (Val.equals("promoted"))
+        RangeVal = LangOptions::ComplexRangeKind::CX_Promoted;
+      else if (Val.equals("basic"))
+        RangeVal = LangOptions::ComplexRangeKind::CX_Basic;
+      else
+        D.Diag(diag::err_drv_unsupported_option_argument)
+            << A->getSpelling() << LangOptions::ComplexRangeKind::CX_None;
+      EmitComplexRangeDiag(D, Range, RangeVal);
+      Range = RangeVal;
       break;
     }
-    case options::OPT_fno_cx_fortran_rules:
-      EmitComplexRangeDiag(D, Range, LangOptions::ComplexRangeKind::CX_Full);
-      Range = LangOptions::ComplexRangeKind::CX_Full;
-      break;
     case options::OPT_ffp_model_EQ: {
       // If -ffp-model= is seen, reset to fno-fast-math
       HonorINFs = true;
@@ -3239,16 +3241,12 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
 
   if (Range != LangOptions::ComplexRangeKind::CX_None)
     ComplexRangeStr = RenderComplexRangeOption(Range);
-  if (!ComplexRangeStr.empty())
+  if (!ComplexRangeStr.empty()) {
     CmdArgs.push_back(Args.MakeArgString(ComplexRangeStr));
-  if (Args.hasArg(options::OPT_fcx_limited_range))
-    CmdArgs.push_back("-fcx-limited-range");
-  if (Args.hasArg(options::OPT_fcx_fortran_rules))
-    CmdArgs.push_back("-fcx-fortran-rules");
-  if (Args.hasArg(options::OPT_fno_cx_limited_range))
-    CmdArgs.push_back("-fno-cx-limited-range");
-  if (Args.hasArg(options::OPT_fno_cx_fortran_rules))
-    CmdArgs.push_back("-fno-cx-fortran-rules");
+    if (Args.hasArg(options::OPT_fcomplex_arithmetic_EQ))
+      CmdArgs.push_back(Args.MakeArgString("-fcomplex-arithmetic=" +
+                                           ComplexRangeKindToStr(Range)));
+  }
 }
 
 static void RenderAnalyzerOptions(const ArgList &Args, ArgStringList &CmdArgs,
diff --git a/clang/lib/Parse/ParsePragma.cpp b/clang/lib/Parse/ParsePragma.cpp
index 730ac1a0fee5cc..87894ef47f8cb6 100644
--- a/clang/lib/Parse/ParsePragma.cpp
+++ b/clang/lib/Parse/ParsePragma.cpp
@@ -909,15 +909,15 @@ void Parser::HandlePragmaCXLimitedRange() {
   LangOptions::ComplexRangeKind Range;
   switch (OOS) {
   case tok::OOS_ON:
-    Range = LangOptions::CX_Limited;
+    Range = LangOptions::CX_Basic;
     break;
   case tok::OOS_OFF:
     Range = LangOptions::CX_Full;
     break;
   case tok::OOS_DEFAULT:
     // According to ISO C99 standard chapter 7.3.4, the default value
-    // for the pragma is ``off'. -fcx-limited-range and -fcx-fortran-rules
-    // control the default value of these pragmas.
+    // for the pragma is ``off'. -fcomplex-arithmetic controls the default value
+    // of these pragmas.
     Range = getLangOpts().getComplexRange();
     break;
   }
diff --git a/clang/test/CodeGen/complex-math.c b/clang/test/CodeGen/complex-math.c
index a44aa0014a6587..ba00b9cbecd2fe 100644
--- a/clang/test/CodeGen/complex-math.c
+++ b/clang/test/CodeGen/complex-math.c
@@ -5,7 +5,7 @@
 // RUN: %clang_cc1 %s -O0 -emit-llvm -triple armv7-none-linux-gnu...
[truncated]

``````````

</details>


https://github.com/llvm/llvm-project/pull/81514
