Re: [patch RFC] SH: PR target/22553

[Joern RENNECKE <joern dot rennecke at st dot com>]

Kaz Kojima wrote:

> Hi,
>
> It seems that target/22553 is one of the 4.1 regressions which
> is critial for sh4-*-linux-gnu.  It causes the build failure
> during libstdc++ build on some systems, though my nightly builds
> on this target couldn't catch it because I'm using slightly
> different libc headers with those of the reporter of that PR.
> The reduced testcase in #2 of the audit trail of the PR fails
> even with the 4.0 compiler.
> Taking a look at it, it seems to be the problem of the first
> scheduling pass in PIC case
:REVIEWMAIL:

No.  With mainline, I see a return value copy torn away from a function
call.
The first step happens very early, more or less during rtl generation:
because the call might trap, it ends a basic block, and the return value
copy is being put in at the start of the following block.

(call_insn 52 49 66 8 (parallel [
           (set (reg:SI 0 r0)
               (call (mem:SI (symbol_ref:SI ("_Z3foov") [flags 0x41] 
<function_decl 0xb5950400 foo>) [0 S4 A32])
                   (const_int 0 [0x0])))
           (use (reg:PSI 151 ))
           (use (reg:SI 12 r12))
           (clobber (reg:SI 146 pr))
           (clobber (scratch:SI))
       ]) 229 {call_value_pcrel} (nil)
   (expr_list:REG_EH_REGION (const_int 1 [0x1])
       (nil))
   (nil))

(note 66 52 53 9 [bb 9] NOTE_INSN_BASIC_BLOCK)

(insn 53 66 54 9 (set (reg/v:SI 159 [ j ])
       (reg:SI 0 r0)) 172 {movsi_ie} (nil)
   (nil))

(jump_insn 54 53 55 9 (set (pc)
       (label_ref 11)) 218 {jump_compact} (nil)
   (nil))

(barrier 55 54 58)

(note 58 55 63 NOTE_INSN_FUNCTION_END)

The second step happens during try_optimize_cfg, called from cleanup_cfg,
called from rest_of_handle_jump2.  The return value copy ends up far in 
front
of the call, near the start of the function.

(barrier 10 9 84)

(code_label 84 10 66 9 28 "" [1 uses])

(note 66 84 53 9 [bb 9] NOTE_INSN_BASIC_BLOCK)

(insn 53 66 15 9 (set (reg/v:SI 159 [ j ])
       (reg:SI 0 r0)) 172 {movsi_ie} (nil)
   (nil))

(insn 15 53 16 9 (set (reg/f:SI 164)
       (const:SI (unspec [
                   (symbol_ref:SI ("k") <var_decl 0xb58bd1b8 k>)
               ] 7))) 172 {movsi_ie} (nil)
   (nil))

.... lots of blocks...

(call_insn 52 49 83 8 (parallel [
           (set (reg:SI 0 r0)
               (call (mem:SI (symbol_ref:SI ("_Z3foov") [flags 0x41] 
<function_decl 0xb5950400 foo>) [0 S4 A32])
                   (const_int 0 [0x0])))
           (use (reg:PSI 151 ))
           (use (reg:SI 12 r12))
           (clobber (reg:SI 146 pr))
           (clobber (scratch:SI))
       ]) 229 {call_value_pcrel} (nil)
   (expr_list:REG_EH_REGION (const_int 1 [0x1])
       (nil))
   (nil))

(note 83 52 85 11 [bb 11] NOTE_INSN_BASIC_BLOCK)

(jump_insn 85 83 86 11 (set (pc)
       (label_ref 84)) -1 (nil)
   (nil))

(barrier 86 85 58)

(note 58 86 63 NOTE_INSN_FUNCTION_END)

(code_label 63 58 68 10 25 "" [2 uses])

(note 68 63 0 10 [bb 10] NOTE_INSN_BASIC_BLOCK)