[libc] Use if constexpr for compile-time conditionals

[frobtech]

Don't use plain if for things that are compile-time constants.
Instead, use if constexpr. This both ensures that these are
properly wired up constant expressions as intended, and prevents
warnings from the compiler about useless if checks that look in
the source like they're meant to do something at runtime but will
just be compiled away.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Roland McGrath (frobtech)

Changes

Don't use plain if for things that are compile-time constants.
Instead, use if constexpr. This both ensures that these are
properly wired up constant expressions as intended, and prevents
warnings from the compiler about useless if checks that look in
the source like they're meant to do something at runtime but will
just be compiled away.

---

Full diff: https://github.com/llvm/llvm-project/pull/113417.diff

1 Files Affected:

• (modified) libc/test/UnitTest/FPMatcher.h (+10-10)

diff --git a/libc/test/UnitTest/FPMatcher.h b/libc/test/UnitTest/FPMatcher.h
index bdcc22ef94e76b..7fcc6a32025b5d 100644
--- a/libc/test/UnitTest/FPMatcher.h
+++ b/libc/test/UnitTest/FPMatcher.h
@@ -124,35 +124,35 @@ template <typename T, TestCond Condition> class CFPMatcher : public Matcher<T> {
 
   bool match(T actualValue) {
     actual = actualValue;
-    if (cpp::is_complex_type_same<T, _Complex float>())
+    if constexpr (cpp::is_complex_type_same<T, _Complex float>())
       return matchComplex<float>();
-    else if (cpp::is_complex_type_same<T, _Complex double>())
+    else if constexpr (cpp::is_complex_type_same<T, _Complex double>())
       return matchComplex<double>();
-    else if (cpp::is_complex_type_same<T, _Complex long double>())
+    else if constexpr (cpp::is_complex_type_same<T, _Complex long double>())
       return matchComplex<long double>();
 #ifdef LIBC_TYPES_HAS_CFLOAT16
-    else if (cpp::is_complex_type_same<T, cfloat16>)
+    else if constexpr (cpp::is_complex_type_same<T, cfloat16>)
       return matchComplex<float16>();
 #endif
 #ifdef LIBC_TYPES_HAS_CFLOAT128
-    else if (cpp::is_complex_type_same<T, cfloat128>)
+    else if constexpr (cpp::is_complex_type_same<T, cfloat128>)
       return matchComplex<float128>();
 #endif
   }
 
   void explainError() override {
-    if (cpp::is_complex_type_same<T, _Complex float>())
+    if constexpr (cpp::is_complex_type_same<T, _Complex float>())
       return explainErrorComplex<float>();
-    else if (cpp::is_complex_type_same<T, _Complex double>())
+    else if constexpr (cpp::is_complex_type_same<T, _Complex double>())
       return explainErrorComplex<double>();
-    else if (cpp::is_complex_type_same<T, _Complex long double>())
+    else if constexpr (cpp::is_complex_type_same<T, _Complex long double>())
       return explainErrorComplex<long double>();
 #ifdef LIBC_TYPES_HAS_CFLOAT16
-    else if (cpp::is_complex_type_same<T, cfloat16>)
+    else if constexpr (cpp::is_complex_type_same<T, cfloat16>)
       return explainErrorComplex<float16>();
 #endif
 #ifdef LIBC_TYPES_HAS_CFLOAT128
-    else if (cpp::is_complex_type_same<T, cfloat128>)
+    else if constexpr (cpp::is_complex_type_same<T, cfloat128>)
       return explainErrorComplex<float128>();
 #endif
   }