Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> 于2023年7月19日周三 14:27写道: > > On Wed, 19 Jul 2023, YunQiang Su wrote: > > > PR #104914 > > > > When work with > > int val; > > ((unsigned char*)&val)[3] = *buf; > > if (val > 0) ... > > The RTX mode is obtained from REG instead of SUBREG, which make > > D<INS> is used instead of <INS>. Thus something wrong happens > > on sign-extend default architectures, like MIPS64. > > > > Let's use str_rtx and mode of str_rtx as the parameters for > > store_integral_bit_field if: > > modes of op0 and str_rtx are INT; > > length of op0 is greater than str_rtx. > > > > This patch has been tested on aarch64-linux-gnu, x86_64-linux-gnu, > > mips64el-linux-gnuabi64 without regression. > > I still think you are "fixing" this in the wrong place. The bugzilla > audit trail points to combine and later notes an eventual expansion > issue (but for another testcase/target). > > You have to explain in more detail on what is wrong with the initial > RTL on mips. >
In the first RTL file, aka xx.c.256r.expand, the zero_extract RTX is like (insn 10 9 11 2 (set (zero_extract:DI (reg/v:DI 200 [ val ]) (const_int 8 [0x8]) (const_int 0 [0])) (subreg:DI (reg:QI 202) 0)) "../xx.c":4:29 -1 (nil)) Not, all of the REG are in DImode. On MIPS64, it will expand to `DINS` instructions. While in fact here, we expect an SImode operation, due to `val` in C code is `int`. With my patch, the RTX will be like: (insn 10 9 11 2 (set (zero_extract:SI (subreg:SI (reg/v:DI 200 [ val ]) 0) (const_int 8 [0x8]) (const_int 0 [0])) (subreg:SI (reg:QI 202) 0)) "xx.c":4:29 -1 (nil)) So the operation will be SImode, aka `INS` instruction for MIPS64. The problem is based on 2 fact/root cause: 1. MIPS's `INS` instruction will be always to sign-extension, while `DINS` won't li $7, 0xff li $8, 0 ins $8,$7,24,8 # set the 24-32 bits of $8 to 0xff. The value of $8 will be 0xff ff ff ff ff 00 00 00. li $7, 0xff li $8, 0 dins $8,$7,24,8 # set the 24-32 bits of $8 to 0xff. The value of $8 will be 0x 00 00 00 00 ff 00 00 00. 2. Due to most of MIPS instructions work with 32bit value, aka instructions without `d` as its first char (in fact with few exception), are sign-extension, the MIPS backend just ignore `extendsidi2`, aka RTX (insn 14 13 15 2 (set (reg/v:DI 200 [ val ]) (sign_extend:DI (subreg:SI (reg/v:DI 200 [ val ]) 0))) "xx.c":5:29 -1 (nil)) > Richard. > > > gcc/ChangeLog: > > PR: 104914. > > * expmed.cc(store_bit_field_1): Pass str_rtx and its mode > > to store_integral_bit_field if the length of op0 is greater > > than str_rtx. > > > > gcc/testsuite/ChangeLog: > > PR: 104914. > > * gcc.target/mips/pr104914.c: New testcase. > > --- > > gcc/expmed.cc | 20 +++++++++++++++++--- > > gcc/testsuite/gcc.target/mips/pr104914.c | 17 +++++++++++++++++ > > 2 files changed, 34 insertions(+), 3 deletions(-) > > create mode 100644 gcc/testsuite/gcc.target/mips/pr104914.c > > > > diff --git a/gcc/expmed.cc b/gcc/expmed.cc > > index fbd4ce2d42f..5531c19e891 100644 > > --- a/gcc/expmed.cc > > +++ b/gcc/expmed.cc > > @@ -850,6 +850,7 @@ store_bit_field_1 (rtx str_rtx, poly_uint64 bitsize, > > poly_uint64 bitnum, > > since that case is valid for any mode. The following cases are only > > valid for integral modes. */ > > opt_scalar_int_mode op0_mode = int_mode_for_mode (GET_MODE (op0)); > > + opt_scalar_int_mode str_mode = int_mode_for_mode (GET_MODE (str_rtx)); > > scalar_int_mode imode; > > if (!op0_mode.exists (&imode) || imode != GET_MODE (op0)) > > { > > @@ -881,9 +882,22 @@ store_bit_field_1 (rtx str_rtx, poly_uint64 bitsize, > > poly_uint64 bitnum, > > op0 = gen_lowpart (op0_mode.require (), op0); > > } > > > > - return store_integral_bit_field (op0, op0_mode, ibitsize, ibitnum, > > - bitregion_start, bitregion_end, > > - fieldmode, value, reverse, fallback_p); > > + /* If MODEs of str_rtx and op0 are INT, and the length of op0 is greater > > than > > + str_rtx, it means that str_rtx has a shorter SUBREG: int32 on 64 > > mach/ABI > > + is an example. For this case, we should use the mode of SUBREG, > > otherwise > > + bad code will generate for sign-extension ports, like MIPS. */ > > + bool use_str_mode = false; > > + if (GET_MODE_CLASS (GET_MODE (str_rtx)) == MODE_INT > > + && GET_MODE_CLASS (GET_MODE (op0)) == MODE_INT > > + && known_gt (GET_MODE_SIZE (GET_MODE (op0)), > > + GET_MODE_SIZE (GET_MODE (str_rtx)))) > > + use_str_mode = true; > > + > > + return store_integral_bit_field (use_str_mode ? str_rtx : op0, > > + use_str_mode ? str_mode : op0_mode, > > + ibitsize, ibitnum, bitregion_start, > > + bitregion_end, fieldmode, value, > > + reverse, fallback_p); > > } > > > > /* Subroutine of store_bit_field_1, with the same arguments, except > > diff --git a/gcc/testsuite/gcc.target/mips/pr104914.c > > b/gcc/testsuite/gcc.target/mips/pr104914.c > > new file mode 100644 > > index 00000000000..fd6ef6af446 > > --- /dev/null > > +++ b/gcc/testsuite/gcc.target/mips/pr104914.c > > @@ -0,0 +1,17 @@ > > +/* { dg-do compile } */ > > +/* { dg-options "-march=mips64r2 -mabi=64" } */ > > + > > +/* { dg-final { scan-assembler-not "\tdins\t" } } */ > > + > > +NOMIPS16 int test (const unsigned char *buf) > > +{ > > + int val; > > + ((unsigned char*)&val)[0] = *buf++; > > + ((unsigned char*)&val)[1] = *buf++; > > + ((unsigned char*)&val)[2] = *buf++; > > + ((unsigned char*)&val)[3] = *buf++; > > + if(val > 0) > > + return 1; > > + else > > + return 0; > > +} > > > > -- > Richard Biener <rguent...@suse.de> > SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, > Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman; > HRB 36809 (AG Nuernberg) -- YunQiang Su