This patch proposes adding run-time library support for bit reversal,
by adding a __bitrevsi2 function to libgcc. Thoughts/opinions?
I'm also tempted to add __popcount[qh]i2 and __parity[qh]i2 to libgcc,
to allow the RTL optimizers to perform narrowing operations, but I'm
curious to hear whether QImode and HImode support, though more efficient,
is frowned by the libgcc maintainers/philosophy.
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32} and
on nvptx-none, with no new regressions. Ok for mainline?
2023-05-06 Roger Sayle <[email protected]>
gcc/ChangeLog
* doc/libgcc.texi (__bitrevqi2): Document bit reversal run-time
functions; __bitrevqi2, __bitrevhi2, __bitrevsi2 and __bitrevdi2.
libgcc/ChangeLog
* Makfile.in (lib2funcs): Add __bitrev[qhsd]i2.
* libgcc-std.ver.in (GCC_14.0.0): Add __bitrev[qhsd]i2.
* libgcc2.c (__bitrevqi2): New function.
(__bitrevhi2): Likewise.
(__bitrevsi2): Likewise.
(__bitrevdi2): Likewise.
* libgcc2.h (__bitrevqi2): Prototype here.
(__bitrevhi2): Likewise.
(__bitrevsi2): Likewise.
(__bitrevdi2): Likewise.
Thanks in advance,
Roger
--
diff --git a/gcc/doc/libgcc.texi b/gcc/doc/libgcc.texi
index 73aa803..7611347 100644
--- a/gcc/doc/libgcc.texi
+++ b/gcc/doc/libgcc.texi
@@ -218,6 +218,13 @@ These functions return the number of bits set in @var{a}.
These functions return the @var{a} byteswapped.
@end deftypefn
+@deftypefn {Runtime Function} int8_t __bitrevqi2 (int8_t @var{a})
+@deftypefnx {Runtime Function} int16_t __bitrevhi2 (int16_t @var{a})
+@deftypefnx {Runtime Function} int32_t __bitrevsi2 (int32_t @var{a})
+@deftypefnx {Runtime Function} int64_t __bitrevdi2 (int64_t @var{a})
+These functions return the bit reversed @var{a}.
+@end deftypefn
+
@node Soft float library routines
@section Routines for floating point emulation
@cindex soft float library
diff --git a/libgcc/Makefile.in b/libgcc/Makefile.in
index 6c4dc79..67c54df 100644
--- a/libgcc/Makefile.in
+++ b/libgcc/Makefile.in
@@ -446,7 +446,7 @@ lib2funcs = _muldi3 _negdi2 _lshrdi3 _ashldi3 _ashrdi3
_cmpdi2 _ucmpdi2 \
_paritysi2 _paritydi2 _powisf2 _powidf2 _powixf2 _powitf2 \
_mulhc3 _mulsc3 _muldc3 _mulxc3 _multc3 _divhc3 _divsc3 \
_divdc3 _divxc3 _divtc3 _bswapsi2 _bswapdi2 _clrsbsi2 \
- _clrsbdi2
+ _clrsbdi2 _bitrevqi2 _bitrevhi2 _bitrevsi2 _bitrevdi2
# The floating-point conversion routines that involve a single-word integer.
# XX stands for the integer mode.
diff --git a/libgcc/libgcc-std.ver.in b/libgcc/libgcc-std.ver.in
index c4f87a5..2198b0e 100644
--- a/libgcc/libgcc-std.ver.in
+++ b/libgcc/libgcc-std.ver.in
@@ -1944,3 +1944,12 @@ GCC_7.0.0 {
__PFX__divmoddi4
__PFX__divmodti4
}
+
+%inherit GCC_14.0.0 GCC_7.0.0
+GCC_14.0.0 {
+ # bit reversal functions
+ __PFX__bitrevqi2
+ __PFX__bitrevhi2
+ __PFX__bitrevsi2
+ __PFX__bitrevdi2
+}
diff --git a/libgcc/libgcc2.c b/libgcc/libgcc2.c
index e0017d1..2bef2a1 100644
--- a/libgcc/libgcc2.c
+++ b/libgcc/libgcc2.c
@@ -488,6 +488,54 @@ __bswapdi2 (DItype u)
| (((u) & 0x00000000000000ffull) << 56));
}
#endif
+
+#ifdef L_bitrevqi2
+QItype
+__bitrevqi2 (QItype x)
+{
+ UQItype u = x;
+ u = (((u) >> 1) & 0x55) | (((u) & 0x55) << 1);
+ u = (((u) >> 2) & 0x33) | (((u) & 0x33) << 2);
+ return ((u) >> 4) | ((u) << 4);
+}
+#endif
+#ifdef L_bitrevhi2
+HItype
+__bitrevhi2 (HItype x)
+{
+ UHItype u = x;
+ u = (((u) >> 1) & 0x5555) | (((u) & 0x5555) << 1);
+ u = (((u) >> 2) & 0x3333) | (((u) & 0x3333) << 2);
+ u = (((u) >> 4) & 0x0f0f) | (((u) & 0x0f0f) << 4);
+ return ((u) >> 8) | ((u) << 8);
+}
+#endif
+#ifdef L_bitrevsi2
+SItype
+__bitrevsi2 (SItype x)
+{
+ USItype u = x;
+ u = (((u) >> 1) & 0x55555555) | (((u) & 0x55555555) << 1);
+ u = (((u) >> 2) & 0x33333333) | (((u) & 0x33333333) << 2);
+ u = (((u) >> 4) & 0x0f0f0f0f) | (((u) & 0x0f0f0f0f) << 4);
+ return __bswapsi2 (u);
+}
+#endif
+#ifdef L_bitrevdi2
+DItype
+__bitrevdi2 (DItype x)
+{
+ UDItype u = x;
+ u = (((u) >> 1) & 0x5555555555555555ll)
+ | (((u) & 0x5555555555555555ll) << 1);
+ u = (((u) >> 2) & 0x3333333333333333ll)
+ | (((u) & 0x3333333333333333ll) << 2);
+ u = (((u) >> 4) & 0x0f0f0f0f0f0f0f0fll)
+ | (((u) & 0x0f0f0f0f0f0f0f0fll) << 4);
+ return __bswapdi2 (u);
+}
+#endif
+
#ifdef L_ffssi2
#undef int
int
diff --git a/libgcc/libgcc2.h b/libgcc/libgcc2.h
index 3ec9bbd..e1abc0d 100644
--- a/libgcc/libgcc2.h
+++ b/libgcc/libgcc2.h
@@ -338,6 +338,10 @@ typedef int shift_count_type __attribute__((mode
(__libgcc_shift_count__)));
#define __udiv_w_sdiv __N(udiv_w_sdiv)
#define __clear_cache __N(clear_cache)
#define __enable_execute_stack __N(enable_execute_stack)
+#define __bitrevqi2 __N(bitrevqi2)
+#define __bitrevhi2 __N(bitrevhi2)
+#define __bitrevsi2 __N(bitrevsi2)
+#define __bitrevdi2 __N(bitrevdi2)
#ifndef __powisf2
#define __powisf2 __N(powisf2)
@@ -426,6 +430,15 @@ extern DWtype __subvDI3 (DWtype, DWtype);
extern DWtype __mulvDI3 (DWtype, DWtype);
extern DWtype __negvDI2 (DWtype);
+extern QItype __bitrevqi2 (QItype);
+extern HItype __bitrevhi2 (HItype);
+#if MIN_UNITS_PER_WORD > 1
+extern SItype __bitrevsi2 (SItype);
+#endif
+#if __SIZEOF_LONG_LONG__ > 4
+extern DItype __bitrevdi2 (DItype);
+#endif
+
#ifdef COMPAT_SIMODE_TRAPPING_ARITHMETIC
#define __absvsi2 __N(absvsi2)
#define __negvsi2 __N(negvsi2)
