================
@@ -247,10 +247,35 @@ llvm::Constant
*CodeGenModule::getBuiltinLibFunction(const FunctionDecl *FD,
Name = Context.BuiltinInfo.getName(BuiltinID).substr(10);
}
+ // If no standard library declaration was found in the AST (freestanding
+ // code calling builtins directly without headers), perform automatic
+ // resolution of MSVC CRT symbol names and DLL import attributes.
+ bool IsNoHeader = (D == GlobalDecl(FD));
+ if (IsNoHeader && getTriple().isWindowsMSVCEnvironment() &&
+ Name == "hypotf") {
+ // Map C99 float math functions to their MSVC CRT prefixed names on
Windows.
+ // (Only hypotf needs mapping as it is not exported without prefix in UCRT
+ // on both x86 and x64).
+ Name = "_hypotf";
----------------
atetubou wrote:
I actually don't know the reason of why hypotf is so special in UCRT, but I
scanned the export symbols of the 32-bit/64-bit Windows UCRT libraries
(`ucrt.lib` and `libucrt.lib` in Windows SDK 10.0.26100.0) and confirmed the
following:
1. **Other C99 float functions are exported normally:**
Functions like `logbf`, `nextafterf`, `sinf`, etc., are exported under their
normal names (without prefix) from the UCRT DLL.
2. **`hypotf` is the only exception:**
`hypotf` is **not exported** under the normal name `hypotf` in UCRT. UCRT
only exports it as `_hypotf` (with the leading underscore), both in the dynamic
import library (`ucrt.lib` -> `__imp__hypotf`) and the static library
(`libucrt.lib` -> `_hypotf`).
(This applies to architectures: x86, x64, and ARM64, but not sure for ARM as
my machine doesn't have libraries for the architecture).
3. **MSVC SDK header implementation:**
In `<corecrt_math.h>`, MSVC defines `hypotf` as an inline function wrapping
`_hypotf`:
```cpp
__inline float hypotf(float _X, float _Y) { return _hypotf(_X, _Y); }
```
Microsoft likely omitted the normal `hypotf` symbol from the UCRT binaries
because they assumed all callers would include the header and inline it to
`_hypotf`.
Since Clang emits CodeGen for the freestanding `__builtin_hypotf` using its
default name `hypotf`, this missing DLL export causes unresolved symbol errors
at link time. Because other C99 float math functions are exported normally,
only `hypotf` needs this compiler-side fallback redirection to `_hypotf`.
https://github.com/llvm/llvm-project/pull/207135
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