Re: c++/9786: [3.2/3.3/3.4 regression] Ice in fixup_abnormal_edges with -fnon-call-exceptions -O2

[Jason Merrill <jason at redhat dot com>]

	`Jason Merrill' changed the state to `analyzed'.


State-Changed-From-To: open-analyzed
State-Changed-By: jason
State-Changed-When: Thu Mar 13 18:24:37 2003
State-Changed-Why:
To compute 0.299*l, gcc generates this code to load l:

(insn 63 62 64 (nil) (set (reg:SF 74)
        (mem/s:SF (reg/v/f:SI 69 [ this ]) [13 <variable>.l+0 S4 A32])) -1 (nil)
    (nil))

(insn 64 63 65 (nil) (set (reg:DF 73)
        (float_extend:DF (reg:SF 74))) -1 (nil)
    (nil))

Both of these are deemed to possibly trap, since they involve floating
point math, so they go in separate basic blocks.  By .32.bbro, we have

(insn 63 216 167 2 0x402a2a24 (set (reg:SF 8 st(0) [orig:74 <variable>.l ] [74])
        (mem/s:SF (reg/v/u/f:SI 0 eax [orig:59 mi ] [59]) [13 <variable>.l+0 S4 A32])) 62 {*movsf_1} (insn_list 216 (nil))
    (expr_list:REG_DEAD (reg/v/u/f:SI 0 eax [orig:59 mi ] [59])
        (expr_list:REG_EH_REGION (const_int 2 [0x2])
            (nil))))
;; End of basic block 2, registers live:
 1 [dx] 6 [bp] 7 [sp] 8 [st] 16 [] 20 [frame]

;; Start of basic block 3, registers live: 1 [dx] 6 [bp] 7 [sp] 8 [st] 16 [] 20 [frame]
(note 167 63 64 3 [bb 3] NOTE_INSN_BASIC_BLOCK)

(insn 64 167 168 3 0x402a2a24 (set (reg:DF 8 st(0) [73])
        (float_extend:DF (reg:SF 8 st(0) [orig:74 <variable>.l ] [74]))) 93 {*extendsfdf2_1} (nil)
    (expr_list:REG_EH_REGION (const_int 2 [0x2])
        (nil)))
;; End of basic block 3, registers live:
 1 [dx] 6 [bp] 7 [sp] 8 [st] 16 [] 20 [frame]

Next, the reg-stack pass decides that insn 64 is a no-op and deletes it.
But that leaves bb3 as an empty basic block with an EH edge, which doesn't
make any sense, and fixup_abnormal_edges aborts.

Is it actually possible for a float_extend to trap?  If not, the simple fix
is to teach may_trap_p about that.  Otherwise, we need to delete the edge
somewhere along the way.