[clang] Adding C23 constexpr math functions fmin and frexp. (PR #88978)

[Zahira Ammarguellat via cfe-commits]

https://github.com/zahiraam created https://github.com/llvm/llvm-project/pull/88978

None

>From 3acc848f4fcc68445dfc849f9c6f8d384d3692af Mon Sep 17 00:00:00 2001
From: Zahira Ammarguellat <zahira.ammarguellat at intel.com>
Date: Tue, 16 Apr 2024 13:09:58 -0700
Subject: [PATCH] Adding C23 constexpr math functions fmin and frexp.

---
 clang/include/clang/Basic/Builtins.td |  4 +--
 clang/lib/AST/ExprConstant.cpp        | 16 ++++++++-
 clang/test/CodeGen/constexpr-math.cpp | 51 +++++++++++++++++++++++++++
 3 files changed, 68 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/CodeGen/constexpr-math.cpp

diff --git a/clang/include/clang/Basic/Builtins.td b/clang/include/clang/Basic/Builtins.td
index 52c0dd52c28b11..a35c77286229ff 100644
--- a/clang/include/clang/Basic/Builtins.td
+++ b/clang/include/clang/Basic/Builtins.td
@@ -3440,7 +3440,7 @@ def Fmod : FPMathTemplate, LibBuiltin<"math.h"> {
 
 def Frexp : FPMathTemplate, LibBuiltin<"math.h"> {
   let Spellings = ["frexp"];
-  let Attributes = [NoThrow];
+  let Attributes = [NoThrow, Constexpr];
   let Prototype = "T(T, int*)";
   let AddBuiltinPrefixedAlias = 1;
 }
@@ -3618,7 +3618,7 @@ def Fmax : FPMathTemplate, LibBuiltin<"math.h"> {
 
 def Fmin : FPMathTemplate, LibBuiltin<"math.h"> {
   let Spellings = ["fmin"];
-  let Attributes = [NoThrow, Const];
+  let Attributes = [NoThrow, Const, Constexpr];
   let Prototype = "T(T, T)";
   let AddBuiltinPrefixedAlias = 1;
   let OnlyBuiltinPrefixedAliasIsConstexpr = 1;
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 5a36621dc5cce2..506621ac7e9c1b 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -2922,7 +2922,7 @@ static bool handleFloatFloatBinOp(EvalInfo &Info, const BinaryOperator *E,
   //   If during the evaluation of an expression, the result is not
   //   mathematically defined [...], the behavior is undefined.
   // FIXME: C++ rules require us to not conform to IEEE 754 here.
-  if (LHS.isNaN()) {
+  if (!Info.getLangOpts().CPlusPlus23 && LHS.isNaN()) {
     Info.CCEDiag(E, diag::note_constexpr_float_arithmetic) << LHS.isNaN();
     return Info.noteUndefinedBehavior();
   }
@@ -14547,6 +14547,18 @@ bool FloatExprEvaluator::VisitCallExpr(const CallExpr *E) {
   default:
     return false;
 
+  case Builtin::BI__builtin_frexpf:
+  case Builtin::BI__builtin_frexp: {
+    LValue Pointer;
+    if (!EvaluateFloat(E->getArg(0), Result, Info) ||
+        !EvaluatePointer(E->getArg(1), Pointer, Info))
+      return false;
+    llvm::RoundingMode RM =
+        E->getFPFeaturesInEffect(Info.Ctx.getLangOpts()).getRoundingMode();
+    int FrexpExp;
+    Result = llvm::frexp(Result, FrexpExp, RM);
+    return true;
+  }
   case Builtin::BI__builtin_huge_val:
   case Builtin::BI__builtin_huge_valf:
   case Builtin::BI__builtin_huge_vall:
@@ -14638,6 +14650,8 @@ bool FloatExprEvaluator::VisitCallExpr(const CallExpr *E) {
     return true;
   }
 
+  case Builtin::BIfmin:
+  case Builtin::BIfminf:
   case Builtin::BI__builtin_fmin:
   case Builtin::BI__builtin_fminf:
   case Builtin::BI__builtin_fminl:
diff --git a/clang/test/CodeGen/constexpr-math.cpp b/clang/test/CodeGen/constexpr-math.cpp
new file mode 100644
index 00000000000000..446bf3f4f7a504
--- /dev/null
+++ b/clang/test/CodeGen/constexpr-math.cpp
@@ -0,0 +1,51 @@
+// RUN: %clang_cc1 -x c++ -triple x86_64-unknown-unknown -std=c++23 \
+// RUN: -emit-llvm -o - %s | FileCheck %s
+
+// RUN %clang_cc1 -x c++ -triple x86_64-linux-gnu -emit-llvm -o - %s \
+// RUN -std=c++23
+
+#define INFINITY ((float)(1e+300 * 1e+300))
+#define NAN      (-(float)(INFINITY * 0.0F))
+
+//constexpr double frexp ( double num, int* exp );
+//constexpr float foo ( float num, int* exp );
+
+int func()
+{
+  int i;
+
+  // fmin
+  constexpr double f1 = __builtin_fmin(15.24, 1.3);
+  constexpr double f2 = __builtin_fmin(-0.0, +0.0);
+  constexpr double f3 = __builtin_fmin(+0.0, -0.0);
+  constexpr float f4 = __builtin_fminf(NAN, NAN);
+  constexpr float f5 = __builtin_fminf(NAN, -1);
+  constexpr float f6 = __builtin_fminf(-INFINITY, 0);
+  constexpr float f7 = __builtin_fminf(INFINITY, 0);
+
+  // frexp
+  constexpr double f8 = __builtin_frexp(123.45, &i);
+  constexpr double f9 = __builtin_frexp(0.0, &i);
+  constexpr double f10 = __builtin_frexp(-0.0, &i);
+  constexpr double f11 = __builtin_frexpf(NAN, &i);
+  constexpr double f12 = __builtin_frexpf(-NAN, &i);
+  constexpr double f13 = __builtin_frexpf(INFINITY, &i);
+  constexpr double f14 = __builtin_frexpf(INFINITY, &i);
+
+  return 0;
+}
+
+// CHECK: store double 1.300000e+00, ptr {{.*}}
+// CHECK: store double -0.000000e+00, ptr {{.*}}
+// CHECK: store double -0.000000e+00, ptr {{.*}}
+// CHECK: store float 0xFFF8000000000000, ptr {{.*}}
+// CHECK: store float -1.000000e+00, ptr {{.*}}
+// CHECK: store float 0xFFF0000000000000, ptr {{.*}}
+
+// CHECK: store double 0x3FEEDCCCCCCCCCCD, ptr {{.*}}
+// CHECK: store double 0.000000e+00, ptr {{.*}}
+// CHECK: store double -0.000000e+00, ptr {{.*}}
+// CHECK: store double 0xFFF8000000000000, ptr {{.*}}
+// CHECK: store double 0x7FF8000000000000, ptr {{.*}}
+// CHECK: store double 0x7FF0000000000000, ptr {{.*}}
+// CHECK: store double 0x7FF0000000000000, ptr {{.*}}