git: 524b018d2004 - main - riscv: Add a soft-float implementation of fabs()

[Alex Richardson]

The branch main has been updated by arichardson:

URL: https://cgit.FreeBSD.org/src/commit/?id=524b018d200408bed5eb0d2b892db5b9fb46808b

commit 524b018d200408bed5eb0d2b892db5b9fb46808b
Author:     Alex Richardson <arichardson at FreeBSD.org>
AuthorDate: 2021-03-01 12:46:30 +0000
Commit:     Alex Richardson <arichardson at FreeBSD.org>
CommitDate: 2021-03-01 12:53:46 +0000

    riscv: Add a soft-float implementation of fabs()
    
    We could just use a C implementation using __builtin_fabs(), but using
    this assembly version guarantees that there is no additional prolog/epilog
    code. Additionally, clang generates worse code for masking off the top bit
    than GCC: https://bugs.llvm.org/show_bug.cgi?id=49377.
    
    This fixes the RISCV64 softfloat world build after cf97d2a1dab8. That commit
    added -fno-builtin to the msun tests which resulted in the first references to
    fabs (previously the compiler inlined all calls).
    
    Reviewed By:    dim
    Reported by:    mjg
    Differential Revision: https://reviews.freebsd.org/D28994
---
 lib/libc/riscv/gen/fabs.S | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/libc/riscv/gen/fabs.S b/lib/libc/riscv/gen/fabs.S
index 44249252e9c1..09042af3b4c0 100644
--- a/lib/libc/riscv/gen/fabs.S
+++ b/lib/libc/riscv/gen/fabs.S
@@ -1,5 +1,6 @@
 /*-
  * Copyright (c) 2015-2017 Ruslan Bukin <br at bsdpad.com>
+ * Copyright (c) 2021 Alex Richardson <arichardson at FreeBSD.org>
  * All rights reserved.
  *
  * Portions of this software were developed by SRI International and the
@@ -10,6 +11,9 @@
  * Computer Laboratory as part of the CTSRD Project, with support from the
  * UK Higher Education Innovation Fund (HEIF).
  *
+ * This work was supported by Innovate UK project 105694, "Digital Security
+ * by Design (DSbD) Technology Platform Prototype".
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
@@ -35,9 +39,12 @@
 #include <machine/asm.h>
 __FBSDID("$FreeBSD$");
 
-#ifdef __riscv_float_abi_double
 ENTRY(fabs)
+#ifdef __riscv_float_abi_double
 	fabs.d	fa0, fa0
+#else
+	slli a0,a0,1
+	srli a0,a0,1
+#endif
 	ret
 END(fabs)
-#endif