From: Daniel Engel <gnu@danielengel.com>
To: Richard Earnshaw <Richard.Earnshaw@foss.arm.com>,
gcc-patches@gcc.gnu.org
Cc: Daniel Engel <gnu@danielengel.com>,
Christophe Lyon <christophe.lyon@linaro.org>
Subject: [PATCH v7 13/34] Import 'ffs' functions from the CM0 library
Date: Mon, 31 Oct 2022 08:45:08 -0700 [thread overview]
Message-ID: <20221031154529.3627576-14-gnu@danielengel.com> (raw)
In-Reply-To: <20221031154529.3627576-1-gnu@danielengel.com>
This implementation provides an efficient tail call to __clzdi2(), making the
functions rather smaller and faster than the C versions.
gcc/libgcc/ChangeLog:
2022-10-09 Daniel Engel <gnu@danielengel.com>
* config/arm/bits/ctz2.S (__ffssi2, __ffsdi2): New functions.
* config/arm/t-elf (LIB1ASMFUNCS): Added _ffssi2 and _ffsdi2.
---
libgcc/config/arm/ctz2.S | 77 +++++++++++++++++++++++++++++++++++++++-
libgcc/config/arm/t-elf | 2 ++
2 files changed, 78 insertions(+), 1 deletion(-)
diff --git a/libgcc/config/arm/ctz2.S b/libgcc/config/arm/ctz2.S
index 82c81c6ae11..d57acabae01 100644
--- a/libgcc/config/arm/ctz2.S
+++ b/libgcc/config/arm/ctz2.S
@@ -1,4 +1,4 @@
-/* ctz2.S: ARM optimized 'ctz' functions
+/* ctz2.S: ARM optimized 'ctz' and related functions
Copyright (C) 2020-2022 Free Software Foundation, Inc.
Contributed by Daniel Engel (gnu@danielengel.com)
@@ -238,3 +238,78 @@ FUNC_END ctzdi2
#endif /* L_ctzsi2 || L_ctzdi2 */
+
+#ifdef L_ffsdi2
+
+// int __ffsdi2(int)
+// Return the index of the least significant 1-bit in $r1:r0,
+// or zero if $r1:r0 is zero. The least significant bit is index 1.
+// Returns the result in $r0.
+// Uses $r2 and possibly $r3 as scratch space.
+// Same section as __ctzsi2() for sake of the tail call branches.
+FUNC_START_SECTION ffsdi2 .text.sorted.libgcc.ctz2.ffsdi2
+ CFI_START_FUNCTION
+
+ // Simplify branching by assuming a non-zero lower word.
+ // For all such, ffssi2(x) == ctzsi2(x) + 1.
+ movs r2, #(33 - CTZ_RESULT_OFFSET)
+
+ #if defined(__ARMEB__) && __ARMEB__
+ // HACK: Save the upper word in a scratch register.
+ movs r3, r0
+
+ // Test the lower word.
+ movs r0, r1
+ bne SYM(__internal_ctzsi2)
+
+ // Test the upper word.
+ movs r2, #(65 - CTZ_RESULT_OFFSET)
+ movs r0, r3
+ bne SYM(__internal_ctzsi2)
+
+ #else /* !__ARMEB__ */
+ // Test the lower word.
+ cmp r0, #0
+ bne SYM(__internal_ctzsi2)
+
+ // Test the upper word.
+ movs r2, #(65 - CTZ_RESULT_OFFSET)
+ movs r0, r1
+ bne SYM(__internal_ctzsi2)
+
+ #endif /* !__ARMEB__ */
+
+ // Upper and lower words are both zero.
+ RET
+
+ CFI_END_FUNCTION
+FUNC_END ffsdi2
+
+#endif /* L_ffsdi2 */
+
+
+#ifdef L_ffssi2
+
+// int __ffssi2(int)
+// Return the index of the least significant 1-bit in $r0,
+// or zero if $r0 is zero. The least significant bit is index 1.
+// Returns the result in $r0.
+// Uses $r2 and possibly $r3 as scratch space.
+// Same section as __ctzsi2() for sake of the tail call branches.
+FUNC_START_SECTION ffssi2 .text.sorted.libgcc.ctz2.ffssi2
+ CFI_START_FUNCTION
+
+ // Simplify branching by assuming a non-zero argument.
+ // For all such, ffssi2(x) == ctzsi2(x) + 1.
+ movs r2, #(33 - CTZ_RESULT_OFFSET)
+
+ // Test for zero, return unmodified.
+ cmp r0, #0
+ bne SYM(__internal_ctzsi2)
+ RET
+
+ CFI_END_FUNCTION
+FUNC_END ffssi2
+
+#endif /* L_ffssi2 */
+
diff --git a/libgcc/config/arm/t-elf b/libgcc/config/arm/t-elf
index 89071cebe45..346fc766f17 100644
--- a/libgcc/config/arm/t-elf
+++ b/libgcc/config/arm/t-elf
@@ -35,6 +35,8 @@ LIB1ASMFUNCS += \
_clrsbdi2 \
_clzdi2 \
_ctzdi2 \
+ _ffssi2 \
+ _ffsdi2 \
_dvmd_tls \
_divsi3 \
_modsi3 \
--
2.34.1
next prev parent reply other threads:[~2022-10-31 15:47 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-31 15:44 [PATCH v7 00/34] libgcc: Thumb-1 Floating-Point Assembly for Cortex M0 Daniel Engel
2022-10-31 15:44 ` [PATCH v7 01/34] Add and restructure function declaration macros Daniel Engel
2022-10-31 15:44 ` [PATCH v7 02/34] Rename THUMB_FUNC_START to THUMB_FUNC_ENTRY Daniel Engel
2022-10-31 15:44 ` [PATCH v7 03/34] Fix syntax warnings on conditional instructions Daniel Engel
2022-10-31 15:44 ` [PATCH v7 04/34] Reorganize LIB1ASMFUNCS object wrapper macros Daniel Engel
2022-10-31 15:45 ` [PATCH v7 05/34] Add the __HAVE_FEATURE_IT and IT() macros Daniel Engel
2022-10-31 15:45 ` [PATCH v7 06/34] Refactor 'clz' functions into a new file Daniel Engel
2022-10-31 15:45 ` [PATCH v7 07/34] Refactor 'ctz' " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 08/34] Refactor 64-bit shift " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 09/34] Import 'clz' functions from the CM0 library Daniel Engel
2022-10-31 15:45 ` [PATCH v7 10/34] Import 'ctz' " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 11/34] Import 64-bit shift " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 12/34] Import 'clrsb' " Daniel Engel
2022-10-31 15:45 ` Daniel Engel [this message]
2022-10-31 15:45 ` [PATCH v7 14/34] Import 'parity' " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 15/34] Import 'popcnt' " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 16/34] Refactor Thumb-1 64-bit comparison into a new file Daniel Engel
2022-10-31 15:45 ` [PATCH v7 17/34] Import 64-bit comparison from CM0 library Daniel Engel
2022-10-31 15:45 ` [PATCH v7 18/34] Merge Thumb-2 optimizations for 64-bit comparison Daniel Engel
2022-10-31 15:45 ` [PATCH v7 19/34] Import 32-bit division from the CM0 library Daniel Engel
2022-10-31 15:45 ` [PATCH v7 20/34] Refactor Thumb-1 64-bit division into a new file Daniel Engel
2022-10-31 15:45 ` [PATCH v7 21/34] Import 64-bit division from the CM0 library Daniel Engel
2022-10-31 15:45 ` [PATCH v7 22/34] Import integer multiplication " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 23/34] Refactor Thumb-1 float comparison into a new file Daniel Engel
2022-10-31 15:45 ` [PATCH v7 24/34] Import float comparison from the CM0 library Daniel Engel
2022-10-31 15:45 ` [PATCH v7 25/34] Refactor Thumb-1 float subtraction into a new file Daniel Engel
2022-10-31 15:45 ` [PATCH v7 26/34] Import float addition and subtraction from the CM0 library Daniel Engel
2022-10-31 15:45 ` [PATCH v7 27/34] Import float multiplication " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 28/34] Import float division " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 29/34] Import integer-to-float conversion " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 30/34] Import float-to-integer " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 31/34] Import float<->double " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 32/34] Import float<->__fp16 " Daniel Engel
2022-10-31 15:45 ` [PATCH v7 33/34] Drop single-precision Thumb-1 soft-float functions Daniel Engel
2022-10-31 15:45 ` [PATCH v7 34/34] Add -mpure-code support to the CM0 functions Daniel Engel
2022-11-15 15:27 ` [PING] Re: [PATCH v7 00/34] libgcc: Thumb-1 Floating-Point Assembly for Cortex M0 Daniel Engel
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