[libc-commits] [libc] [libc] Fix feature check for riscv (PR #145169)

[Mikhail R. Gadelha via libc-commits]

https://github.com/mikhailramalho created https://github.com/llvm/llvm-project/pull/145169

This PR fixes the feature detection for RISC-V floating-point support in LLVM's libc implementation.

The `__riscv_flen` macro represents the floating-point register width in bits (32, 64, or 128). Since Extension D is specifically documented as implying F, we can use simple >= comparisons to detect them. 

For half-precision support, the implementation checks for the Zfhmin extension as RVA22 and RVA23 profiles only require Zfhmin rather than the full Zfh extension. Zfh also implies Zfhmin, so checking for Zfhmin should cover all cases.


>From 218e30090486613ba6d28ce70a77623eb6379ee1 Mon Sep 17 00:00:00 2001
From: "Mikhail R. Gadelha" <mikhail at igalia.com>
Date: Sat, 21 Jun 2025 10:37:10 -0300
Subject: [PATCH] Fix feature check for riscv

Signed-off-by: Mikhail R. Gadelha <mikhail at igalia.com>
---
 libc/src/__support/macros/properties/cpu_features.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libc/src/__support/macros/properties/cpu_features.h b/libc/src/__support/macros/properties/cpu_features.h
index 3677e1fc3275c..457a2b7869d40 100644
--- a/libc/src/__support/macros/properties/cpu_features.h
+++ b/libc/src/__support/macros/properties/cpu_features.h
@@ -61,15 +61,15 @@
 
 #if defined(__riscv_flen)
 // https://github.com/riscv-non-isa/riscv-c-api-doc/blob/main/src/c-api.adoc
-#if (__riscv_flen & 0x10)
+#if (__riscv_arch_test && __riscv_zfhmin)
 #define LIBC_TARGET_CPU_HAS_RISCV_FPU_HALF
 #define LIBC_TARGET_CPU_HAS_FPU_HALF
 #endif // LIBC_TARGET_CPU_HAS_RISCV_FPU_HALF
-#if (__riscv_flen & 0x20)
+#if (__riscv_flen >= 32)
 #define LIBC_TARGET_CPU_HAS_RISCV_FPU_FLOAT
 #define LIBC_TARGET_CPU_HAS_FPU_FLOAT
 #endif // LIBC_TARGET_CPU_HAS_RISCV_FPU_FLOAT
-#if (__riscv_flen & 0x40)
+#if (__riscv_flen >= 64)
 #define LIBC_TARGET_CPU_HAS_RISCV_FPU_DOUBLE
 #define LIBC_TARGET_CPU_HAS_FPU_DOUBLE
 #endif // LIBC_TARGET_CPU_HAS_RISCV_FPU_DOUBLE