From: Daniel Engel <g...@danielengel.com>
gcc/libgcc/ChangeLog:
2021-01-07 Daniel Engel <g...@danielengel.com>
* config/arm/eabi/idiv.S: New file for __udivsi3() and __divsi3().
* config/arm/lib1funcs.S: #include eabi/idiv.S (v6m only).
---
libgcc/config/arm/eabi/idiv.S | 299 ++++++++++++++++++++++++++++++++++
libgcc/config/arm/lib1funcs.S | 19 ++-
2 files changed, 317 insertions(+), 1 deletion(-)
create mode 100644 libgcc/config/arm/eabi/idiv.S
diff --git a/libgcc/config/arm/eabi/idiv.S b/libgcc/config/arm/eabi/idiv.S
new file mode 100644
index 00000000000..7381e8f57a3
--- /dev/null
+++ b/libgcc/config/arm/eabi/idiv.S
@@ -0,0 +1,299 @@
+/* div.S: Thumb-1 size-optimized 32-bit integer division
+
+ Copyright (C) 2018-2021 Free Software Foundation, Inc.
+ Contributed by Daniel Engel, Senva Inc (g...@danielengel.com)
+
+ This file is free software; you can redistribute it and/or modify it
+ under the terms of the GNU General Public License as published by the
+ Free Software Foundation; either version 3, or (at your option) any
+ later version.
+
+ This file is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ General Public License for more details.
+
+ Under Section 7 of GPL version 3, you are granted additional
+ permissions described in the GCC Runtime Library Exception, version
+ 3.1, as published by the Free Software Foundation.
+
+ You should have received a copy of the GNU General Public License and
+ a copy of the GCC Runtime Library Exception along with this program;
+ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+ <http://www.gnu.org/licenses/>. */
+
+
+#ifndef __GNUC__
+
+// int __aeabi_idiv0(int)
+// Helper function for division by 0.
+WEAK_START_SECTION aeabi_idiv0 .text.sorted.libgcc.idiv.idiv0
+FUNC_ALIAS cm0_idiv0 aeabi_idiv0
+ CFI_START_FUNCTION
+
+ #if defined(TRAP_EXCEPTIONS) && TRAP_EXCEPTIONS
+ svc #(SVC_DIVISION_BY_ZERO)
+ #endif
+
+ RET
+
+ CFI_END_FUNCTION
+FUNC_END cm0_idiv0
+FUNC_END aeabi_idiv0
+
+#endif /* !__GNUC__ */
+
+
+#ifdef L_divsi3
+
+// int __aeabi_idiv(int, int)
+// idiv_return __aeabi_idivmod(int, int)
+// Returns signed $r0 after division by $r1.
+// Also returns the signed remainder in $r1.
+// Same parent section as __divsi3() to keep branches within range.
+FUNC_START_SECTION divsi3 .text.sorted.libgcc.idiv.divsi3
+
+#ifndef __symbian__
+ FUNC_ALIAS aeabi_idiv divsi3
+ FUNC_ALIAS aeabi_idivmod divsi3
+#endif
+
+ CFI_START_FUNCTION
+
+ // Extend signs.
+ asrs r2, r0, #31
+ asrs r3, r1, #31
+
+ // Absolute value of the denominator, abort on division by zero.
+ eors r1, r3
+ subs r1, r3
+ #if defined(PEDANTIC_DIV0) && PEDANTIC_DIV0
+ beq LLSYM(__idivmod_zero)
+ #else
+ beq SYM(__uidivmod_zero)
+ #endif
+
+ // Absolute value of the numerator.
+ eors r0, r2
+ subs r0, r2
+
+ // Keep the sign of the numerator in bit[31] (for the remainder).
+ // Save the XOR of the signs in bits[15:0] (for the quotient).
+ push { rT, lr }
+ .cfi_remember_state
+ .cfi_adjust_cfa_offset 8
+ .cfi_rel_offset rT, 0
+ .cfi_rel_offset lr, 4
+
+ lsrs rT, r3, #16
+ eors rT, r2
+
+ // Handle division as unsigned.
+ bl SYM(__uidivmod_nonzero) __PLT__
+
+ // Set the sign of the remainder.
+ asrs r2, rT, #31
+ eors r1, r2
+ subs r1, r2
+
+ // Set the sign of the quotient.
+ sxth r3, rT
+ eors r0, r3
+ subs r0, r3
+
+ LLSYM(__idivmod_return):
+ pop { rT, pc }
+ .cfi_restore_state
+
+ #if defined(PEDANTIC_DIV0) && PEDANTIC_DIV0
+ LLSYM(__idivmod_zero):
+ // Set up the *div0() parameter specified in the ARM runtime ABI:
+ // * 0 if the numerator is 0,
+ // * Or, the largest value of the type manipulated by the calling
+ // division function if the numerator is positive,
+ // * Or, the least value of the type manipulated by the calling
+ // division function if the numerator is negative.
+ subs r1, r0
+ orrs r0, r1
+ asrs r0, #31
+ lsrs r0, #1
+ eors r0, r2
+
+ // At least the __aeabi_idiv0() call is common.
+ b SYM(__uidivmod_zero2)
+ #endif /* PEDANTIC_DIV0 */
+
+ CFI_END_FUNCTION
+FUNC_END divsi3
+
+#ifndef __symbian__
+ FUNC_END aeabi_idiv
+ FUNC_END aeabi_idivmod
+#endif
+
+#endif /* L_divsi3 */
+
+
+#ifdef L_udivsi3
+
+// int __aeabi_uidiv(unsigned int, unsigned int)
+// idiv_return __aeabi_uidivmod(unsigned int, unsigned int)
+// Returns unsigned $r0 after division by $r1.
+// Also returns the remainder in $r1.
+FUNC_START_SECTION udivsi3 .text.sorted.libgcc.idiv.udivsi3
+
+#ifndef __symbian__
+ FUNC_ALIAS aeabi_uidiv udivsi3
+ FUNC_ALIAS aeabi_uidivmod udivsi3
+#endif
+
+ CFI_START_FUNCTION
+
+ // Abort on division by zero.
+ tst r1, r1
+ #if defined(PEDANTIC_DIV0) && PEDANTIC_DIV0
+ beq LLSYM(__uidivmod_zero)
+ #else
+ beq SYM(__uidivmod_zero)
+ #endif
+
+ #if defined(OPTIMIZE_SPEED) && OPTIMIZE_SPEED
+ // MAYBE: Optimize division by a power of 2
+ #endif
+
+ // Public symbol for the sake of divsi3().
+ FUNC_ENTRY uidivmod_nonzero
+ // Pre division: Shift the denominator as far as possible left
+ // without making it larger than the numerator.
+ // The loop is destructive, save a copy of the numerator.
+ mov ip, r0
+
+ // Set up binary search.
+ movs r3, #16
+ movs r2, #1
+
+ LLSYM(__uidivmod_align):
+ // Prefer dividing the numerator to multipying the denominator
+ // (multiplying the denominator may result in overflow).
+ lsrs r0, r3
+ cmp r0, r1
+ blo LLSYM(__uidivmod_skip)
+
+ // Multiply the denominator and the result together.
+ lsls r1, r3
+ lsls r2, r3
+
+ LLSYM(__uidivmod_skip):
+ // Restore the numerator, and iterate until search goes to 0.
+ mov r0, ip
+ lsrs r3, #1
+ bne LLSYM(__uidivmod_align)
+
+ // In The result $r3 has been conveniently initialized to 0.
+ b LLSYM(__uidivmod_entry)
+
+ LLSYM(__uidivmod_loop):
+ // Scale the denominator and the quotient together.
+ lsrs r1, #1
+ lsrs r2, #1
+ beq LLSYM(__uidivmod_return)
+
+ LLSYM(__uidivmod_entry):
+ // Test if the denominator is smaller than the numerator.
+ cmp r0, r1
+ blo LLSYM(__uidivmod_loop)
+
+ // If the denominator is smaller, the next bit of the result is '1'.
+ // If the new remainder goes to 0, exit early.
+ adds r3, r2
+ subs r0, r1
+ bne LLSYM(__uidivmod_loop)
+
+ LLSYM(__uidivmod_return):
+ mov r1, r0
+ mov r0, r3
+ RET
+
+ #if defined(PEDANTIC_DIV0) && PEDANTIC_DIV0
+ LLSYM(__uidivmod_zero):
+ // Set up the *div0() parameter specified in the ARM runtime ABI:
+ // * 0 if the numerator is 0,
+ // * Or, the largest value of the type manipulated by the calling
+ // division function if the numerator is positive.
+ subs r1, r0
+ orrs r0, r1
+ asrs r0, #31
+
+ FUNC_ENTRY uidivmod_zero2
+ #if defined(DOUBLE_ALIGN_STACK) && DOUBLE_ALIGN_STACK
+ push { rT, lr }
+ .cfi_remember_state
+ .cfi_adjust_cfa_offset 8
+ .cfi_rel_offset rT, 0
+ .cfi_rel_offset lr, 4
+ #else
+ push { lr }
+ .cfi_remember_state
+ .cfi_adjust_cfa_offset 4
+ .cfi_rel_offset lr, 0
+ #endif
+
+ // Since GCC implements __aeabi_idiv0() as a weak overridable function,
+ // this call must be prepared for a jump beyond +/- 2 KB.
+ // NOTE: __aeabi_idiv0() can't be implemented as a tail call, since any
+ // non-trivial override will (likely) corrupt a remainder in $r1.
+ bl SYM(__aeabi_idiv0) __PLT__
+
+ // Since the input to __aeabi_idiv0() was INF, there really isn't any
+ // choice in which of the recommended *divmod() patterns to follow.
+ // Clear the remainder to complete {INF, 0}.
+ eors r1, r1
+
+ #if defined(DOUBLE_ALIGN_STACK) && DOUBLE_ALIGN_STACK
+ pop { rT, pc }
+ .cfi_restore_state
+ #else
+ pop { pc }
+ .cfi_restore_state
+ #endif
+
+ #else /* !PEDANTIC_DIV0 */
+ FUNC_ENTRY uidivmod_zero
+ // NOTE: The following code sets up a return pair of {0, numerator},
+ // the second preference given by the ARM runtime ABI specification.
+ // The pedantic version is 18 bytes larger between __aeabi_idiv() and
+ // __aeabi_uidiv(). However, this version does not conform to the
+ // out-of-line parameter requirements given for __aeabi_idiv0(), and
+ // also does not pass 'gcc/testsuite/gcc.target/arm/divzero.c'.
+
+ // Since the numerator may be overwritten by __aeabi_idiv0(), save now.
+ // Afterwards, it can be restored directly as the remainder.
+ push { r0, lr }
+ .cfi_remember_state
+ .cfi_adjust_cfa_offset 8
+ .cfi_rel_offset r0, 0
+ .cfi_rel_offset lr, 4
+
+ // Set up the quotient (not ABI compliant).
+ eors r0, r0
+
+ // Since GCC implements div0() as a weak overridable function,
+ // this call must be prepared for a jump beyond +/- 2 KB.
+ bl SYM(__aeabi_idiv0) __PLT__
+
+ // Restore the remainder and return.
+ pop { r1, pc }
+ .cfi_restore_state
+
+ #endif /* !PEDANTIC_DIV0 */
+
+ CFI_END_FUNCTION
+FUNC_END udivsi3
+
+#ifndef __symbian__
+ FUNC_END aeabi_uidiv
+ FUNC_END aeabi_uidivmod
+#endif
+
+#endif /* L_udivsi3 */
+
diff --git a/libgcc/config/arm/lib1funcs.S b/libgcc/config/arm/lib1funcs.S
index 6aed09f4930..6657f3b5749 100644
--- a/libgcc/config/arm/lib1funcs.S
+++ b/libgcc/config/arm/lib1funcs.S
@@ -1090,6 +1090,10 @@ LSYM(Ldivbyzero_negative):
/* ------------------------------------------------------------------------ */
/* Start of the Real Functions */
/* ------------------------------------------------------------------------ */
+
+/* Disable these on v6m in favor of 'eabi/idiv.S', below. */
+#ifndef NOT_ISA_TARGET_32BIT
+
#ifdef L_udivsi3
#if defined(__prefer_thumb__)
@@ -1495,6 +1499,18 @@ LSYM(Lover12):
DIV_FUNC_END modsi3 signed
#endif /* L_modsi3 */
+
+#else /* NOT_ISA_TARGET_32BIT */
+/* Temp registers. */
+#define rP r4
+#define rQ r5
+#define rS r6
+#define rT r7
+
+#define PEDANTIC_DIV0 (1)
+#include "eabi/idiv.S"
+#endif /* NOT_ISA_TARGET_32BIT */
+
/* ------------------------------------------------------------------------ */
#ifdef L_dvmd_tls
@@ -1512,7 +1528,8 @@ LSYM(Lover12):
FUNC_END div0
#endif
-#endif /* L_divmodsi_tools */
+#endif /* L_div_tls */
+
/* ------------------------------------------------------------------------ */
#ifdef L_dvmd_lnx
@ GNU/Linux division-by zero handler. Used in place of L_dvmd_tls
--
2.25.1
