rtl: Try to remove EH edges after {pro,epi}logue generation [PR90259]

rtl: Try to remove EH edges after {pro,epi}logue generation [PR90259]

After prologue and epilogue generation, the judgement on whether
one memory access onto stack frame may trap or not could change,
since we get more exact stack information by now.

As PR90259 shows, some memory access becomes impossible to trap
any more after prologue and epilogue generation, it can make
subsequent optimization be able to remove it if safe, but it
results in unexpected control flow status due to REG_EH_REGION
note missing.

This patch proposes to try to remove EH edges with function
purge_all_dead_edges after prologue and epilogue generation,
it simplifies CFG as early as we can and don't need any fixup
in downstream passes.

CFG simplification result with PR90259's case as example:

*before*

   18: %1:TF=call [`__gcc_qdiv'] argc:0
      REG_EH_REGION 0x2
   77: NOTE_INSN_BASIC_BLOCK 3
   19: NOTE_INSN_DELETED
   20: NOTE_INSN_DELETED
  110: [%31:SI+0x20]=%1:DF
      REG_EH_REGION 0x2
  116: NOTE_INSN_BASIC_BLOCK 4
  111: [%31:SI+0x28]=%2:DF
      REG_EH_REGION 0x2
   22: NOTE_INSN_BASIC_BLOCK 5
  108: %0:DF=[%31:SI+0x20]
      REG_EH_REGION 0x2
  117: NOTE_INSN_BASIC_BLOCK 6
  109: %1:DF=[%31:SI+0x28]
      REG_EH_REGION 0x2
   79: NOTE_INSN_BASIC_BLOCK 7
   26: [%31:SI+0x18]=%0:DF
  104: pc=L69
  105: barrier

*after*

   18: %1:TF=call [`__gcc_qdiv'] argc:0
      REG_EH_REGION 0x2
   77: NOTE_INSN_BASIC_BLOCK 3
   19: NOTE_INSN_DELETED
   20: NOTE_INSN_DELETED
  110: [%31:SI+0x20]=%1:DF
  111: [%31:SI+0x28]=%2:DF
  108: %0:DF=[%31:SI+0x20]
  109: %1:DF=[%31:SI+0x28]
   26: [%31:SI+0x18]=%0:DF
  104: pc=L69
  105: barrier

	PR rtl-optimization/90259

gcc/ChangeLog:

	* function.cc (rest_of_handle_thread_prologue_and_epilogue): Add
	parameter fun, and call function purge_all_dead_edges.
	(pass_thread_prologue_and_epilogue::execute): Name unamed parameter
	as fun, and use it for rest_of_handle_thread_prologue_and_epilogue.

gcc/testsuite/ChangeLog:

	* g++.target/powerpc/pr90259.C: New.