toolchain/gcc/4.3.2/900-if-ifcvt-noce_emit_store_flag.patch

   1 Date: Mon, 29 Sep 2008 17:11:55 +0000 (UTC)
   2 From: "Joseph S dot  Myers"
   3 Subject: Fix if-conversion bug reversing conditions
   4 Message-ID: <Pine.LNX.4.64.0809291710170.16546@digraph.polyomino.org.uk>
   5
   6 This patch fixes an if-conversion problem that manifested itself in a
   7 4.3-based toolchain as execution failures on powerpc-linux-gnu
   8 -msoft-float:
   9
  10 FAIL: gcc.c-torture/execute/stdarg-3.c execution,  -O3 -fomit-frame-pointer -funroll-loops
  11 FAIL: gcc.c-torture/execute/stdarg-3.c execution,  -O3 -fomit-frame-pointer -funroll-all-loops -finline-functions
  12
  13 I don't have a testcase manifesting the bug on trunk but believe it is
  14 still present there.
  15
  16 A loop is unrolled, and an initial test for whether it has an even or
  17 an odd number of iterations gets wrongly inverted by the post-combine
  18 if-conversion pass (ce2).  After combine the relevant insns (for a
  19 reduced version of stdarg-3.c with the 4.3-based toolchain) look like:
  20
  21 (insn 144 113 145 3 (parallel [
  22             (set (reg:CC 166)
  23                 (compare:CC (zero_extract:SI (reg/v:SI 120 [ j ])
  24                         (const_int 1 [0x1])
  25                         (const_int 31 [0x1f]))
  26                     (const_int 0 [0x0])))
  27             (clobber (scratch:SI))
  28         ]) 159 {*extzvsi_internal1} (nil))
  29
  30 (jump_insn 145 144 70 3 (set (pc)
  31         (if_then_else (ne (reg:CC 166)
  32                 (const_int 0 [0x0]))
  33             (label_ref:SI 178)
  34             (pc))) 560 {*rs6000.md:13937} (expr_list:REG_DEAD (reg:CC 166)
  35         (expr_list:REG_BR_PROB (const_int 5000 [0x1388])
  36             (nil))))
  37 ;; End of basic block 3 -> ( 7 4)
  38
  39 ;; Succ edge  7 [50.0%]
  40 ;; Succ edge  4 [50.0%]  (fallthru)
  41
  42 ...
  43
  44 ;; Start of basic block ( 3) -> 7
  45
  46 ;; Pred edge  3 [50.0%]
  47 (code_label 178 81 137 7 11 "" [1 uses])
  48
  49 (note 137 178 139 7 [bb 7] NOTE_INSN_BASIC_BLOCK)
  50
  51 (insn 139 137 181 7 stdarg-3.c:13 (set (reg/v:SI 120 [ j ])
  52         (plus:SI (reg/v:SI 120 [ j ])
  53             (const_int -1 [0xffffffffffffffff]))) 79 {*addsi3_internal1} (nil))
  54
  55 (jump_insn 181 139 182 7 (set (pc)
  56         (label_ref 70)) -1 (nil))
  57 ;; End of basic block 7 -> ( 4)
  58
  59 find_if_header duly enters noce_find_if_block with then_edge being the
  60 EDGE_FALLTHRU edge (to block 4) and ELSE_EDGE being the edge to block
  61 7.  This reaches the IF-ELSE-JOIN case and sets then_else_reversed, so
  62 then_bb, insn_a as set in noce_process_if_block, is now block 7.
  63 noce_get_condition duly inverts the jump condition.  This is correct
  64 so far; if_info->cond is meant to be the condition for going to
  65 if_info->insn_b (though the comments never say so explicitly, a lot of
  66 code only makes sense that way).
  67
  68 The code in question - subtracting 1 from a REG in the insn_a case
  69 (i.e. if if_info->cond is false) - is handled by noce_try_addcc.  This
  70 reaches the
  71
  72       /* If that fails, construct conditional increment or decrement using
  73          setcc.  */
  74
  75 case and so calls noce_emit_store_flag with REVERSEP set to 1.  Thus
  76 noce_emit_store_flag knows to store the reverse of if_info->cond,
  77 which would be the right value to subtract.  However, it then runs
  78 into the case
  79
  80   /* If earliest == jump, or when the condition is complex, try to
  81      build the store_flag insn directly.  */
  82
  83 where it uses the condition from the original jump, ignoring the
  84 possibility of this condition having been reversed in order to get the
  85 correct insn_b condition.
  86
  87 This patch makes noce_emit_store_flag check the same conditions as
  88 noce_get_condition for whether to reverse the condition, when it goes
  89 back to the original jump.
  90
  91 Bootstrapped with no regressions on i686-pc-linux-gnu.  Tested with no
  92 regressions with cross to powerpc-linux-gnu -msoft-float.  OK to
  93 commit?
  94
  95 2008-09-29  Joseph Myers  <joseph@codesourcery.com>
  96
  97         * ifcvt.c (noce_emit_store_flag): If using condition from original
  98         jump, reverse it if if_info->cond was reversed.
  99
 100 Index: ifcvt.c
 101 ===================================================================
 102 --- gcc-4.3.2.old/gcc/ifcvt.c   (revision 140752)
 103 +++ gcc-4.3.2/gcc/ifcvt.c       (working copy)
 104 @@ -666,7 +666,15 @@
 105       build the store_flag insn directly.  */
 106
 107    if (cond_complex)
 108 -    cond = XEXP (SET_SRC (pc_set (if_info->jump)), 0);
 109 +    {
 110 +      rtx set = pc_set (if_info->jump);
 111 +      cond = XEXP (SET_SRC (set), 0);
 112 +      if (GET_CODE (XEXP (SET_SRC (set), 2)) == LABEL_REF
 113 +         && XEXP (XEXP (SET_SRC (set), 2), 0) == JUMP_LABEL (if_info->jump))
 114 +       reversep = !reversep;
 115 +      if (if_info->then_else_reversed)
 116 +       reversep = !reversep;
 117 +    }
 118
 119    if (reversep)
 120      code = reversed_comparison_code (cond, if_info->jump);
 121