[clang] [libcxx] [PowerPC] Emit libcall to frexpl for calls to frexp(ppcDoublDouble) (PR #75226)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Lei Huang (lei137)

<details>
<summary>Changes</summary>

On Linux PPC call lib func ``frexpl`` for calls to ``frexp()`` for input of type PPCDoubleDouble.

Fixes bug: https://github.com/llvm/llvm-project/issues/64426

---
Full diff: https://github.com/llvm/llvm-project/pull/75226.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/CGBuiltin.cpp (+15-1) 
- (modified) libcxx/test/libcxx/numerics/c.math/constexpr-cxx23-clang.pass.cpp (-6) 


``````````diff
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index 83d0a72aac549..7a700155149e8 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -137,6 +137,10 @@ llvm::Constant *CodeGenModule::getBuiltinLibFunction(const FunctionDecl *FD,
       {Builtin::BI__builtin_modfl, "modf"},
   };
 
+  static SmallDenseMap<unsigned, StringRef, 4> PPCDoubleDoubleBuiltins{
+      {Builtin::BI__builtin_frexpl, "frexpl"},
+  };
+
   // If the builtin has been declared explicitly with an assembler label,
   // use the mangled name. This differs from the plain label on platforms
   // that prefix labels.
@@ -149,6 +153,10 @@ llvm::Constant *CodeGenModule::getBuiltinLibFunction(const FunctionDecl *FD,
         &getTarget().getLongDoubleFormat() == &llvm::APFloat::IEEEquad() &&
         F128Builtins.contains(BuiltinID))
       Name = F128Builtins[BuiltinID];
+    else if (getTriple().isPPC() && getTriple().isOSLinux() &&
+        &getTarget().getLongDoubleFormat() == &llvm::APFloat::PPCDoubleDouble()
+        && PPCDoubleDoubleBuiltins.contains(BuiltinID))
+      Name = PPCDoubleDoubleBuiltins[BuiltinID];
     else if (getTriple().isOSAIX() &&
              &getTarget().getLongDoubleFormat() ==
                  &llvm::APFloat::IEEEdouble() &&
@@ -3410,9 +3418,15 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
                                    { Src0->getType(), Src1->getType() });
     return RValue::get(Builder.CreateCall(F, { Src0, Src1 }));
   }
+  case Builtin::BI__builtin_frexpl: {
+    auto &Triple = getTarget().getTriple();
+    if (Triple.isPPC() && Triple.isOSLinux() &&
+        &getTarget().getLongDoubleFormat() == &llvm::APFloat::PPCDoubleDouble())
+      break;
+    LLVM_FALLTHROUGH;
+  }
   case Builtin::BI__builtin_frexp:
   case Builtin::BI__builtin_frexpf:
-  case Builtin::BI__builtin_frexpl:
   case Builtin::BI__builtin_frexpf128:
   case Builtin::BI__builtin_frexpf16:
     return RValue::get(emitFrexpBuiltin(*this, E, Intrinsic::frexp));
diff --git a/libcxx/test/libcxx/numerics/c.math/constexpr-cxx23-clang.pass.cpp b/libcxx/test/libcxx/numerics/c.math/constexpr-cxx23-clang.pass.cpp
index 31511064ce7ca..a07260a34516f 100644
--- a/libcxx/test/libcxx/numerics/c.math/constexpr-cxx23-clang.pass.cpp
+++ b/libcxx/test/libcxx/numerics/c.math/constexpr-cxx23-clang.pass.cpp
@@ -58,15 +58,9 @@ int main(int, char**) {
 
   ASSERT_NOT_CONSTEXPR_CXX23(std::frexp(0.0f, &DummyInt) == 0.0f);
   ASSERT_NOT_CONSTEXPR_CXX23(std::frexp(0.0, &DummyInt) == 0.0);
-//FIXME: currently linux powerpc does not support this expansion
-// since 0.0L lowers to ppcf128 and special handling is required.
-#if !defined(__LONG_DOUBLE_IBM128__)
   ASSERT_NOT_CONSTEXPR_CXX23(std::frexp(0.0L, &DummyInt) == 0.0L);
-#endif
   ASSERT_NOT_CONSTEXPR_CXX23(std::frexpf(0.0f, &DummyInt) == 0.0f);
-#if !defined(__LONG_DOUBLE_IBM128__)
   ASSERT_NOT_CONSTEXPR_CXX23(std::frexpl(0.0L, &DummyInt) == 0.0L);
-#endif
 
   ASSERT_NOT_CONSTEXPR_CXX23(std::ilogb(1.0f) == 0);
   ASSERT_NOT_CONSTEXPR_CXX23(std::ilogb(1.0) == 0);

``````````

</details>


https://github.com/llvm/llvm-project/pull/75226