Submitted by Uros Bizjak on Sept. 27, 2012, 1:04 p.m.

Message ID | CAFULd4aSLiau+Qa9vC_eUsPrRKwvAqYt=uXxGi5Sj5GphCYMmA@mail.gmail.com |
---|---|

State | New |

Headers | show |

Uros Bizjak <ubizjak@gmail.com> writes: > On Wed, Sep 26, 2012 at 11:22 PM, Eric Botcazou <ebotcazou@adacore.com> wrote: >>> I agree (subreg:M (op:N A C) 0) to (op:M (subreg:N (A 0)) C) is >>> a good transformation, but why do we need to handle as special >>> the case where the subreg is itself the operand of a plus or minus? >>> I think it should happen regardless of where the subreg occurs. >> >> Don't we need to restrict this to the low part though? > > I have tried this approach with attached patch. Unfortunately, > although it survived bootstrap without libjava on x86_64, it failed > building libjava with: > > /home/uros/gcc-svn/trunk/libjava/classpath/javax/swing/plaf/basic/BasicSliderUI.java:1299:0: > error: insn does not satisfy its constraints: > } > ^ > (insn 237 398 399 7 (set (reg:SI 1 dx [125]) > (plus:SI (subreg:SI (mult:DI (reg:DI 1 dx [orig:72 D.78627 ] [72]) > (const_int 2 [0x2])) 0) > (reg:SI 5 di))) > /home/uros/gcc-svn/trunk/libjava/classpath/javax/swing/plaf/basic/BasicSliderUI.java:1271 > 240 {*leasi} > (expr_list:REG_DEAD (reg:DI 5 di) > (nil))) > > Original RTX was (subreg:SI (plus:DI (mult:DI (...) reg:DI))), which > is valid RTX pattern for lea insn, the above is not. > > Due to these problems, I think the safer approach is to limit the > transformation to (plus:SI (subreg:SI (plus:DI (...) 0)) RTXes, as was > the case with original patch. This approach would fix a specific > problem where simplify_plus_minus is not able to simplify the combined > RTX at combine time. Please note, that combined RTXes are always > checked for correctness at combine pass. I think instead the (subreg (plus ...)) handling should be applied to (subreg (mult ...)) too. IMO the correct form of the above address ought to be: (set (reg:SI 1 dx [125]) (plus:SI (mult:SI (reg:SI 1 dx [orig:72 D.78627 ] [72]) (const_int 2 [0x2])) (reg:SI 5 di)) Richard

Index: simplify-rtx.c =================================================================== --- simplify-rtx.c (revision 191796) +++ simplify-rtx.c (working copy) @@ -5689,6 +5688,21 @@ simplify_subreg (enum machine_mode outermode, rtx return CONST0_RTX (outermode); } + /* Simplify (subreg:SI (plus:DI ((x:DI) (y:DI)), 0) + to (plus:SI (subreg:SI (x:DI) 0) (subreg:SI (x:DI) 0)), where + the outer subreg is effectively a truncation to the original mode. */ + if ((GET_CODE (op) == PLUS + || GET_CODE (op) == MINUS) + && SCALAR_INT_MODE_P (outermode) + && SCALAR_INT_MODE_P (innermode) + && GET_MODE_PRECISION (outermode) < GET_MODE_PRECISION (innermode) + && subreg_lsb_1 (outermode, innermode, byte) == 0) + return simplify_gen_binary (GET_CODE (op), outermode, + simplify_gen_subreg (outermode, XEXP (op, 0), + innermode, 0), + simplify_gen_subreg (outermode, XEXP (op, 1), + innermode, 0)); + /* Simplify (subreg:QI (lshiftrt:SI (sign_extend:SI (x:QI)) C), 0) into to (ashiftrt:QI (x:QI) C), where C is a suitable small constant and the outer subreg is effectively a truncation to the original mode. */