Message ID | 50EAA074.3050402@mentor.com |
---|---|
State | New |
Headers | show |
On 01/07/2013 02:16 AM, Tom de Vries wrote: > - /* If MODE is no wider than a single word, we return a paradoxical > - SUBREG. */ > + /* If MODE is no wider than a single word, we return a > + lowpart or paradoxical SUBREG. */ > if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD) > - return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0); > + { > + if (GET_MODE_SIZE (mode) < GET_MODE_SIZE (GET_MODE (op))) > + return gen_lowpart_SUBREG (mode, op); > + else > + return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0); > + } Is there any good reason we're using gen_rtx_SUBREG directly here? Seems like this sort of logic would be present in plain gen_lowpart, generating the paradoxical subreg that we want. r~
Index: gcc/optabs.c =================================================================== --- gcc/optabs.c (revision 194898) +++ gcc/optabs.c (working copy) @@ -329,7 +329,8 @@ widen_operand (rtx op, enum machine_mode /* If MODE is no wider than a single word, we return a paradoxical SUBREG. */ - if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD) + if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD + && GET_MODE_SIZE (mode) > GET_MODE_SIZE (GET_MODE (op))) return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0); /* Otherwise, get an object of MODE, clobber it, and set the low-order
[with CC to gcc-patches] -------- Original Message -------- Subject: [PATCH] Fix PR55876 - Make generation of paradoxical subreg in widen_operand more robust Date: Mon, 07 Jan 2013 11:13:49 +0100 From: Tom de Vries <Tom_deVries@mentor.com> To: Richard Henderson <rth@redhat.com> CC: Steve Ellcey <sellcey@mips.com>, Andrew Pinski <pinskia@gmail.com> Richard, Consider test-case test.c: ... static inline unsigned char bar (const char *b) { unsigned char used = 0; int i; for (i = 0; i < 4; ++i) if (b[i] != 'F') used = 1; return used; } static char buffer[8]; unsigned char foo (void) { return bar (buffer) ? 0 : 1; } ... When compiling test.c with a mips compiler, this ICE triggers: ... $ ./install/bin/mips-linux-gnu-gcc -O3 test.c -S -mabi=64 -march=mips64 test.c: In function 'foo': test.c:19:3: internal compiler error: in gen_rtx_SUBREG, at emit-rtl.c:776 return bar (buffer) ? 0 : 1; ... The ICE is introduced by revision r193539 discussed at http://gcc.gnu.org/ml/gcc-patches/2012-11/msg01148.html . The representation of foo just before expand is this: ... foo () { unsigned charD.13 usedD.1407; charD.2 _7; unsigned charD.13 _13; charD.2 _19; charD.2 _28; charD.2 _37; ;; basic block 2, loop depth 0 ;; pred: ENTRY # VUSE <.MEM_1(D)> _19 = MEM[(const charD.2 *)&bufferD.1387]; used_20 = _19 != 70 ? 1 : 0; # VUSE <.MEM_1(D)> _28 = MEM[(const charD.2 *)&bufferD.1387 + 1B]; used_29 = _28 == 70 ? used_20 : 1; # VUSE <.MEM_1(D)> _37 = MEM[(const charD.2 *)&bufferD.1387 + 2B]; used_38 = _37 == 70 ? used_29 : 1; # VUSE <.MEM_1(D)> _7 = MEM[(const charD.2 *)&bufferD.1387 + 3B]; used_10 = _7 == 70 ? used_38 : 1; _13 = used_10 ^ 1; # VUSE <.MEM_1(D)> return _13; ;; succ: EXIT } ... The used_10 operand is in a DImode reg because r193539 allows it to be promoted while expanding used_10 = _7 == 70 ? used_38 : 1 in expand_cond_expr_using_cmove. The ICE happens during expansion of _13 = used_10 ^ 1 when trying to widen the DIMode reg for use_10 from QImode to SImode: ... #6 0x085d7da5 in widen_operand (op=0xf7cd2ec0, mode=SImode, oldmode=QImode, unsignedp=1, no_extend=1) at /home/vries/local/mips/upstream/src/gcc-mainline/gcc/optabs.c:333 333 return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0); (gdb) call debug_rtx (op) (reg:DI 222 [ used+-7 ]) ... And although the comment in widen_operand states that we're generating a paradoxical subreg: ... /* If MODE is no wider than a single word, we return a paradoxical SUBREG. */ if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD) return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0); ... it's not because mode == SImode and GET_MODE (op) == DImode. Then validate_subreg triggers the ICE in gen_rtx_SUBREG by returning false here: ... /* For pseudo registers, we want most of the same checks. Namely: If the register no larger than a word, the subreg must be lowpart. If the register is larger than a word, the subreg must be the lowpart of a subword. A subreg does *not* perform arbitrary bit extraction. Given that we've already checked mode/offset alignment, we only have to check subword subregs here. */ if (osize < UNITS_PER_WORD && ! (lra_in_progress && (FLOAT_MODE_P (imode) || FLOAT_MODE_P (omode)))) { enum machine_mode wmode = isize > UNITS_PER_WORD ? word_mode : imode; unsigned int low_off = subreg_lowpart_offset (omode, wmode); if (offset % UNITS_PER_WORD != low_off) return false; } ... For a valid pseudo subreg with outer mode SImode and inner mode DImode we need the offset corresponding to the lowpart, which is 4 for -EB. But since we were trying to generate a paradoxical subreg, the offset is 0. This explains why the assert doesn't trigger with -EL. Attached patch (build and tested for target mips-linux-gnu) prevents the ICE by checking in widen_operand whether the result of the gen_rtx_SUBREG call would indeed be a paradoxical subreg. As a consequence, it handles this case now here: ... /* Otherwise, get an object of MODE, clobber it, and set the low-order part to OP. */ result = gen_reg_rtx (mode); emit_clobber (result); emit_move_insn (gen_lowpart (GET_MODE (op), result), op); return result; ... So the generated code is this: ... (insn 34 33 35 2 (clobber (reg:SI 228)) -1 (nil)) (insn 35 34 36 2 (set (subreg:DI (reg:SI 228) 0) (reg:DI 222 [ usedD.1407+-7 ])) -1 (nil)) (insn 36 35 37 2 (set (reg:SI 229) (xor:SI (reg:SI 228) (const_int 1 [0x1]))) -1 ... which is correct. I've just realized that this is probably a too conservative fix. Using this patch: ... ... we generate this instead: ... (insn 34 33 35 2 (set (reg:SI 228) (xor:SI (subreg:SI (reg:DI 222 [ usedD.1407+-7 ]) 4) (const_int 1 [0x1]))) -1 ... which is similar to what we generate with trunk for -EL. So, is the attached patch ok for trunk? Or should I test the more optimal patch listed above? Or should this be fixed somewhere else? Thanks, - Tom 2013-01-07 Tom de Vries <tom@codesourcery.com> PR target/55876 * optabs.c (optabs.c): Add condition to ensure that subreg will be paradoxical.