[PATCH v7 17/34] Import 64-bit comparison from CM0 library

[Daniel Engel <gnu@danielengel.com>]

These are 2-5 instructions smaller and just as fast.  Branches are
minimized, which will allow easier adaptation to Thumb-2/ARM mode.

gcc/libgcc/ChangeLog:
2022-10-09 Daniel Engel <gnu@danielengel.com>

	* config/arm/eabi/lcmp.S (__aeabi_lcmp, __aeabi_ulcmp): Replaced;
	add macro configuration to build __cmpdi2() and __ucmpdi2().
	* config/arm/t-elf (LIB1ASMFUNCS): Added _cmpdi2 and _ucmpdi2.
---
 libgcc/config/arm/eabi/lcmp.S | 151 +++++++++++++++++++++++++---------
 libgcc/config/arm/t-elf       |   2 +
 2 files changed, 112 insertions(+), 41 deletions(-)

diff --git a/libgcc/config/arm/eabi/lcmp.S b/libgcc/config/arm/eabi/lcmp.S
index 336db1d398c..99c7970ecba 100644
--- a/libgcc/config/arm/eabi/lcmp.S
+++ b/libgcc/config/arm/eabi/lcmp.S
@@ -1,8 +1,7 @@
-/* Miscellaneous BPABI functions.  Thumb-1 implementation, suitable for ARMv4T,
-   ARMv6-M and ARMv8-M Baseline like ISA variants.
+/* lcmp.S: Thumb-1 optimized 64-bit integer comparison
 
-   Copyright (C) 2006-2020 Free Software Foundation, Inc.
-   Contributed by CodeSourcery.
+   Copyright (C) 2018-2022 Free Software Foundation, Inc.
+   Contributed by Daniel Engel, Senva Inc (gnu@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
@@ -24,50 +23,120 @@
    <http://www.gnu.org/licenses/>.  */
 
 
+#if defined(L_aeabi_lcmp) || defined(L_cmpdi2)
+
 #ifdef L_aeabi_lcmp
+  #define LCMP_NAME aeabi_lcmp
+  #define LCMP_SECTION .text.sorted.libgcc.lcmp
+#else
+  #define LCMP_NAME cmpdi2
+  #define LCMP_SECTION .text.sorted.libgcc.cmpdi2
+#endif
+
+// int __aeabi_lcmp(long long, long long)
+// int __cmpdi2(long long, long long)
+// Compares the 64 bit signed values in $r1:$r0 and $r3:$r2.
+// lcmp() returns $r0 = { -1, 0, +1 } for orderings { <, ==, > } respectively.
+// cmpdi2() returns $r0 = { 0, 1, 2 } for orderings { <, ==, > } respectively.
+// Object file duplication assumes typical programs follow one runtime ABI.
+FUNC_START_SECTION LCMP_NAME LCMP_SECTION
+    CFI_START_FUNCTION
+
+        // Calculate the difference $r1:$r0 - $r3:$r2.
+        subs    xxl,    yyl
+        sbcs    xxh,    yyh
+
+        // With $r2 free, create a known offset value without affecting
+        //  the N or Z flags.
+        // BUG? The originally unified instruction for v6m was 'mov r2, r3'.
+        //  However, this resulted in a compile error with -mthumb:
+        //    "MOV Rd, Rs with two low registers not permitted".
+        // Since unified syntax deprecates the "cpy" instruction, shouldn't
+        //  there be a backwards-compatible tranlation available?
+        cpy     r2,     r3
+
+        // Evaluate the comparison result.
+        blt     LLSYM(__lcmp_lt)
+
+        // The reference offset ($r2 - $r3) will be +2 iff the first
+        //  argument is larger, otherwise the offset value remains 0.
+        adds    r2,     #2
+
+        // Check for zero (equality in 64 bits).
+        // It doesn't matter which register was originally "hi".
+        orrs    r0,    r1
+
+        // The result is already 0 on equality.
+        beq     LLSYM(__lcmp_return)
+
+    LLSYM(__lcmp_lt):
+        // Create +1 or -1 from the offset value defined earlier.
+        adds    r3,     #1
+        subs    r0,     r2,     r3
+
+    LLSYM(__lcmp_return):
+      #ifdef L_cmpdi2
+        // Offset to the correct output specification.
+        adds    r0,     #1
+      #endif
 
-FUNC_START aeabi_lcmp
-        cmp     xxh, yyh
-        beq     1f
-        bgt     2f
-        movs    r0, #1
-        negs    r0, r0
-        RET
-2:
-        movs    r0, #1
-        RET
-1:
-        subs    r0, xxl, yyl
-        beq     1f
-        bhi     2f
-        movs    r0, #1
-        negs    r0, r0
-        RET
-2:
-        movs    r0, #1
-1:
         RET
-        FUNC_END aeabi_lcmp
 
-#endif /* L_aeabi_lcmp */
+    CFI_END_FUNCTION
+FUNC_END LCMP_NAME
+
+#endif /* L_aeabi_lcmp || L_cmpdi2 */
+
+
+#if defined(L_aeabi_ulcmp) || defined(L_ucmpdi2)
 
 #ifdef L_aeabi_ulcmp
+  #define ULCMP_NAME aeabi_ulcmp
+  #define ULCMP_SECTION .text.sorted.libgcc.ulcmp
+#else
+  #define ULCMP_NAME ucmpdi2
+  #define ULCMP_SECTION .text.sorted.libgcc.ucmpdi2
+#endif
+
+// int __aeabi_ulcmp(unsigned long long, unsigned long long)
+// int __ucmpdi2(unsigned long long, unsigned long long)
+// Compares the 64 bit unsigned values in $r1:$r0 and $r3:$r2.
+// ulcmp() returns $r0 = { -1, 0, +1 } for orderings { <, ==, > } respectively.
+// ucmpdi2() returns $r0 = { 0, 1, 2 } for orderings { <, ==, > } respectively.
+// Object file duplication assumes typical programs follow one runtime ABI.
+FUNC_START_SECTION ULCMP_NAME ULCMP_SECTION
+    CFI_START_FUNCTION
+
+        // Calculate the 'C' flag.
+        subs    xxl,    yyl
+        sbcs    xxh,    yyh
+
+        // Capture the carry flg.
+        // $r2 will contain -1 if the first value is smaller,
+        //  0 if the first value is larger or equal.
+        sbcs    r2,     r2
+
+        // Check for zero (equality in 64 bits).
+        // It doesn't matter which register was originally "hi".
+        orrs    r0,     r1
+
+        // The result is already 0 on equality.
+        beq     LLSYM(__ulcmp_return)
+
+        // Assume +1.  If -1 is correct, $r2 will override.
+        movs    r0,     #1
+        orrs    r0,     r2
+
+    LLSYM(__ulcmp_return):
+      #ifdef L_ucmpdi2
+        // Offset to the correct output specification.
+        adds    r0,     #1
+      #endif
 
-FUNC_START aeabi_ulcmp
-        cmp     xxh, yyh
-        bne     1f
-        subs    r0, xxl, yyl
-        beq     2f
-1:
-        bcs     1f
-        movs    r0, #1
-        negs    r0, r0
-        RET
-1:
-        movs    r0, #1
-2:
         RET
-        FUNC_END aeabi_ulcmp
 
-#endif /* L_aeabi_ulcmp */
+    CFI_END_FUNCTION
+FUNC_END ULCMP_NAME
+
+#endif /* L_aeabi_ulcmp || L_ucmpdi2 */
 
diff --git a/libgcc/config/arm/t-elf b/libgcc/config/arm/t-elf
index 2e3f04aa2f0..83325410097 100644
--- a/libgcc/config/arm/t-elf
+++ b/libgcc/config/arm/t-elf
@@ -41,6 +41,8 @@ LIB1ASMFUNCS += \
 	_ffsdi2 \
 	_paritydi2 \
 	_popcountdi2 \
+	_cmpdi2 \
+	_ucmpdi2 \
 	_dvmd_tls \
 	_divsi3 \
 	_modsi3 \
-- 
2.34.1