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Re: [PING] Re: Add const char* constructors for exception classes in <stdexcept>

From: Oleg Endo <oleg dot endo at t-online dot de>
To: Jonathan Wakely <jwakely dot gcc at gmail dot com>
Cc: "libstdc++ at gcc dot gnu dot org" <libstdc++ at gcc dot gnu dot org>, gcc-patches <gcc-patches at gcc dot gnu dot org>
Date: Wed, 29 Jan 2014 23:45:18 +0100
Subject: Re: [PING] Re: Add const char* constructors for exception classes in <stdexcept>
Authentication-results: sourceware.org; auth=none
References: <1387411826 dot 2455 dot 325 dot camel at yam-132-YW-E178-FTW> <CAH6eHdTK93RwatvT+m_1TLv7Ni=yQ=wDi6v7Hq=jT=O=ZSffzw at mail dot gmail dot com> <1387466908 dot 2455 dot 355 dot camel at yam-132-YW-E178-FTW> <1390745736 dot 22215 dot 207 dot camel at yam-132-YW-E178-FTW> <20140129152136 dot GA21735 at redhat dot com> <1391030247 dot 13654 dot 9 dot camel at yam-132-YW-E178-FTW> <CAH6eHdQXvD27Y83cpEtoJRH7=3mAfujzd4=GKDBiT-G08SK-pg at mail dot gmail dot com>

On Wed, 2014-01-29 at 21:38 +0000, Jonathan Wakely wrote:
> On 29 January 2014 21:17, Oleg Endo wrote:
> > My original intention was to eliminate code bloat when doing something
> > like  throw std::logic_error ("cold coffee");
> > If the const char* overloads are inlined it will emit code to construct
> > an std::string from const char* in user code where the exception is
> > being constructed over and over again.  The idea was to move that code
> > into the std library.
> 
> That's exactly what happens today with the constructors that only take
> a std::string, so it wouldn't be any worse than what we have now,
> would it?

Sorry, I'm not sure I understand your question.  Maybe you meant "any
better than what we have"?  Anyway, I've attached two outputs that show
what I mean.  The version with the const char* ctor overloads
implemented in the library is significantly shorter in the throwing path
(5x function call vs. 7x function call + other inlined std::string ctor
code).

> 
> > BTW the original patch was posted during Stage 3 (19.12.2013).  I don't
> > mind waiting until Stage 1 if adding exports now is a problem.
> 
> OK, let's wait and decide how we want to do it properly in stage 1.

Sure.  Actually I've missed some of the other exception types in
system_error, which should be added, too.  That would eliminate the
   TODO: Add const char* ctors to all exceptions.

I'd also propose moving the system_error ctor implementations into the
library as well, for the same reasons as above.

> 
> (If we're going to make various changes that impact the ABI during the
> next stage 1 we might even want to consider changing the
> std::exception base class to store something like a
> std::shared_ptr<std::string> so that copying an exception object will
> never throw an exception, which is something I've been thinking about
> recently.)

Wouldn't using std::shared_ptr<std::string> introduce an additional heap
allocation when creating the exception, though?
How about storing the exception message in a plain zero terminated
string instead?  This would require only one heap allocation if the
string data is prefixed with a refcount variable.  Basically,
std::make_shared re-invented because it doesn't work with arrays.
Or maybe implement N3640 + N3641 first (even if for library internal use
only as a start)...

Cheers,
Oleg

	.file	"sh_tmp.cpp"
	.text
	.little
	.section	.rodata.str1.4,"aMS",@progbits,1
	.align 2
.LC0:
	.string	"multiplication by zero"
	.text
	.align 1
	.align 2
	.global	__Z6test03ii
	.type	__Z6test03ii, @function
__Z6test03ii:
.LFB746:
	.cfi_startproc
	.cfi_personality 0,___gxx_personality_v0
	.cfi_lsda 0xb,.LLSDA746
	mov.l	r8,@-r15	! 183	movsi_ie/9	[length = 2]
	.cfi_def_cfa_offset 4
	.cfi_offset 8, -4
	mov.l	r9,@-r15	! 184	movsi_ie/9	[length = 2]
	.cfi_def_cfa_offset 8
	.cfi_offset 9, -8
	sts.l	pr,@-r15	! 185	movsi_ie/11	[length = 2]
	.cfi_def_cfa_offset 12
	.cfi_offset 17, -12
	add	#-8,r15	! 186	*addsi3_compact	[length = 2]
	.cfi_def_cfa_offset 20
	tst	r5,r5	! 7	cmpeqsi_t/1	[length = 2]
	bt/s	.L19	! 8	*cbranch_t	[length = 2]
	mul.l	r5,r4	! 68	mul_l	[length = 2]
	sts	macl,r0	! 116	movsi_ie/7	[length = 2]
	add	#8,r15	! 191	*addsi3_compact	[length = 2]
	.cfi_remember_state
	.cfi_def_cfa_offset 12
	lds.l	@r15+,pr	! 193	movsi_ie/15	[length = 2]
	.cfi_restore 17
	.cfi_def_cfa_offset 8
	mov.l	@r15+,r9	! 194	movsi_ie/6	[length = 2]
	.cfi_restore 9
	.cfi_def_cfa_offset 4
	rts		! 197	*return_i	[length = 2]
	mov.l	@r15+,r8	! 195	movsi_ie/6	[length = 2]
	.cfi_def_cfa_offset 0
	.cfi_restore 8
	.align 1
.L19:
	.cfi_restore_state
	mov.l	.L21,r0	! 171	movsi_ie/1	[length = 2]
	jsr	@r0	! 12	call_valuei	[length = 2]
	mov	#8,r4	! 11	movsi_ie/3	[length = 2]
	mov.l	.L22,r1	! 170	movsi_ie/1	[length = 2]
	mov	r15,r4	! 174	movsi_ie/2	[length = 2]
	mov	r15,r6	! 175	movsi_ie/2	[length = 2]
	mov	r0,r9	! 13	movsi_ie/2	[length = 2]
	add	#4,r4	! 19	*addsi3_compact	[length = 2]
	mov.l	.L23,r5	! 20	movsi_ie/1	[length = 2]
.LEHB0:
	jsr	@r1	! 22	calli	[length = 2]
	add	#2,r6	! 21	*addsi3_compact	[length = 2]
.LEHE0:
	mov.l	.L24,r1	! 169	movsi_ie/1	[length = 2]
	mov	r15,r5	! 176	movsi_ie/2	[length = 2]
	mov	r9,r4	! 26	movsi_ie/2	[length = 2]
.LEHB1:
	jsr	@r1	! 28	calli	[length = 2]
	add	#4,r5	! 27	*addsi3_compact	[length = 2]
.LEHE1:
	mov.l	@(4,r15),r1	! 32	movsi_ie/6	[length = 2]
	mov.l	.L33,r2	! 34	movsi_ie/1	[length = 2]
	mov	r1,r4	! 177	movsi_ie/2	[length = 2]
	add	#-12,r4	! 33	*addsi3_compact	[length = 2]
	cmp/eq	r2,r4	! 35	cmpeqsi_t/3	[length = 2]
	bf/s	.L20	! 36	*cbranch_t	[length = 2]
	add	#-64,r1	! 42	*addsi3_compact	[length = 2]
.L4:
	mov.l	.L26,r1	! 167	movsi_ie/1	[length = 2]
	mov.l	.L27,r5	! 62	movsi_ie/1	[length = 2]
	mov.l	.L28,r6	! 63	movsi_ie/1	[length = 2]
.LEHB2:
	jsr	@r1	! 64	calli	[length = 2]
	mov	r9,r4	! 61	movsi_ie/2	[length = 2]
	.align 1
.L11:
	mov	r4,r8	! 123	movsi_ie/2	[length = 2]
.L17:
	mov.l	.L34,r1	! 147	movsi_ie/1	[length = 2]
	lds.l	@r1+,fpscr	! 207	fpu_switch/2	[length = 2]
.L10:
	mov.l	.L30,r1	! 165	movsi_ie/1	[length = 2]
	jsr	@r1	! 109	calli	[length = 2]
	mov	r9,r4	! 108	movsi_ie/2	[length = 2]
	mov.l	.L31,r1	! 164	movsi_ie/1	[length = 2]
	jsr	@r1	! 113	calli	[length = 2]
	mov	r8,r4	! 112	movsi_ie/2	[length = 2]
.LEHE2:
	.align 1
.L20:
	mov.l	@(60,r1),r2	! 43	movsi_ie/6	[length = 2]
	mov	r2,r3	! 178	movsi_ie/2	[length = 2]
	add	#-1,r3	! 45	*addsi3_compact	[length = 2]
	cmp/pl	r2	! 48	cmpgtsi_t/1	[length = 2]
	bt/s	.L4	! 49	*cbranch_t	[length = 2]
	mov.l	r3,@(60,r1)	! 46	movsi_ie/9	[length = 2]
	mov.l	.L35,r1	! 168	movsi_ie/1	[length = 2]
	mov	r15,r5	! 179	movsi_ie/2	[length = 2]
	jsr	@r1	! 55	calli	[length = 2]
	add	#3,r5	! 54	*addsi3_compact	[length = 2]
	bra	.L4
	nop	! 215	jump_compact	[length = 4]
	.align 1
.L12:
	mov.l	@(4,r15),r1	! 77	movsi_ie/6	[length = 2]
	mov	r4,r8	! 129	movsi_ie/2	[length = 2]
	mov.l	.L33,r2	! 79	movsi_ie/1	[length = 2]
	mov	r1,r4	! 180	movsi_ie/2	[length = 2]
	add	#-12,r4	! 78	*addsi3_compact	[length = 2]
	cmp/eq	r2,r4	! 80	cmpeqsi_t/3	[length = 2]
	bt	.L17	! 81	*cbranch_t	[length = 2]
	add	#-64,r1	! 87	*addsi3_compact	[length = 2]
	mov.l	@(60,r1),r2	! 88	movsi_ie/6	[length = 2]
	mov	r2,r3	! 181	movsi_ie/2	[length = 2]
	add	#-1,r3	! 90	*addsi3_compact	[length = 2]
	cmp/pl	r2	! 93	cmpgtsi_t/1	[length = 2]
	bt/s	.L17	! 94	*cbranch_t	[length = 2]
	mov.l	r3,@(60,r1)	! 91	movsi_ie/9	[length = 2]
	mov.l	.L34,r1	! 153	movsi_ie/1	[length = 2]
	mov	r15,r5	! 182	movsi_ie/2	[length = 2]
	lds.l	@r1+,fpscr	! 208	fpu_switch/2	[length = 2]
	mov.l	.L35,r1	! 166	movsi_ie/1	[length = 2]
	jsr	@r1	! 100	calli	[length = 2]
	add	#3,r5	! 99	*addsi3_compact	[length = 2]
	bra	.L10
	nop	! 217	jump_compact	[length = 4]
.L36:
	.align 2
.L21:
	.long	___cxa_allocate_exception
.L22:
	.long	__ZNSsC1EPKcRKSaIcE
.L23:
	.long	.LC0
.L24:
	.long	__ZNSt11logic_errorC1ERKSs
.L33:
	.long	__ZNSs4_Rep20_S_empty_rep_storageE
.L26:
	.long	___cxa_throw
.L27:
	.long	__ZTISt11logic_error
.L28:
	.long	__ZNSt11logic_errorD1Ev
.L34:
	.long	___fpscr_values+4
.L30:
	.long	___cxa_free_exception
.L31:
	.long	__Unwind_Resume
.L35:
	.long	__ZNSs4_Rep10_M_destroyERKSaIcE
	.cfi_endproc
.LFE746:
	.global	___gxx_personality_v0
	.section	.gcc_except_table,"a",@progbits
.LLSDA746:
	.byte	0xff
	.byte	0xff
	.byte	0x1
	.uleb128 .LLSDACSE746-.LLSDACSB746
.LLSDACSB746:
	.uleb128 .LEHB0-.LFB746
	.uleb128 .LEHE0-.LEHB0
	.uleb128 .L11-.LFB746
	.uleb128 0
	.uleb128 .LEHB1-.LFB746
	.uleb128 .LEHE1-.LEHB1
	.uleb128 .L12-.LFB746
	.uleb128 0
	.uleb128 .LEHB2-.LFB746
	.uleb128 .LEHE2-.LEHB2
	.uleb128 0
	.uleb128 0
.LLSDACSE746:
	.text
	.size	__Z6test03ii, .-__Z6test03ii

	.file	"sh_tmp.cpp"
	.text
	.little
	.section	.rodata.str1.4,"aMS",@progbits,1
	.align 2
.LC0:
	.string	"multiplication by zero"
	.text
	.align 1
	.align 2
	.global	__Z6test03ii
	.type	__Z6test03ii, @function
__Z6test03ii:
.LFB746:
	.cfi_startproc
	.cfi_personality 0,___gxx_personality_v0
	.cfi_lsda 0xb,.LLSDA746
	tst	r5,r5	! 7	cmpeqsi_t/1	[length = 2]
	bt/s	.L9	! 8	*cbranch_t	[length = 2]
	mul.l	r5,r4	! 31	mul_l	[length = 2]
	rts		! 81	*simple_return_i	[length = 2]
	sts	macl,r0	! 47	movsi_ie/7	[length = 2]
	.align 1
.L9:
	mov.l	r8,@-r15	! 73	movsi_ie/9	[length = 2]
	.cfi_def_cfa_offset 4
	.cfi_offset 8, -4
	mov.l	r9,@-r15	! 74	movsi_ie/9	[length = 2]
	.cfi_def_cfa_offset 8
	.cfi_offset 9, -8
	sts.l	pr,@-r15	! 75	movsi_ie/11	[length = 2]
	.cfi_def_cfa_offset 12
	.cfi_offset 17, -12
	mov.l	.L10,r0	! 71	movsi_ie/1	[length = 2]
	jsr	@r0	! 12	call_valuei	[length = 2]
	mov	#8,r4	! 11	movsi_ie/3	[length = 2]
	mov.l	.L11,r1	! 70	movsi_ie/1	[length = 2]
	mov	r0,r8	! 13	movsi_ie/2	[length = 2]
	mov.l	.L12,r5	! 18	movsi_ie/1	[length = 2]
.LEHB0:
	jsr	@r1	! 19	calli	[length = 2]
	mov	r0,r4	! 17	movsi_ie/2	[length = 2]
.LEHE0:
	mov.l	.L13,r1	! 69	movsi_ie/1	[length = 2]
	mov.l	.L14,r5	! 25	movsi_ie/1	[length = 2]
	mov.l	.L15,r6	! 26	movsi_ie/1	[length = 2]
.LEHB1:
	jsr	@r1	! 27	calli	[length = 2]
	mov	r8,r4	! 24	movsi_ie/2	[length = 2]
	.align 1
.L4:
	mov.l	.L16,r1	! 64	movsi_ie/1	[length = 2]
	mov	r4,r9	! 54	movsi_ie/2	[length = 2]
	lds.l	@r1+,fpscr	! 82	fpu_switch/2	[length = 2]
	mov.l	.L17,r1	! 68	movsi_ie/1	[length = 2]
	jsr	@r1	! 40	calli	[length = 2]
	mov	r8,r4	! 39	movsi_ie/2	[length = 2]
	mov.l	.L18,r1	! 67	movsi_ie/1	[length = 2]
	jsr	@r1	! 44	calli	[length = 2]
	mov	r9,r4	! 43	movsi_ie/2	[length = 2]
.LEHE1:
.L19:
	.align 2
.L10:
	.long	___cxa_allocate_exception
.L11:
	.long	__ZNSt11logic_errorC1EPKc
.L12:
	.long	.LC0
.L13:
	.long	___cxa_throw
.L14:
	.long	__ZTISt11logic_error
.L15:
	.long	__ZNSt11logic_errorD1Ev
.L16:
	.long	___fpscr_values+4
.L17:
	.long	___cxa_free_exception
.L18:
	.long	__Unwind_Resume
	.cfi_endproc
.LFE746:
	.global	___gxx_personality_v0
	.section	.gcc_except_table,"a",@progbits
.LLSDA746:
	.byte	0xff
	.byte	0xff
	.byte	0x1
	.uleb128 .LLSDACSE746-.LLSDACSB746
.LLSDACSB746:
	.uleb128 .LEHB0-.LFB746
	.uleb128 .LEHE0-.LEHB0
	.uleb128 .L4-.LFB746
	.uleb128 0
	.uleb128 .LEHB1-.LFB746
	.uleb128 .LEHE1-.LEHB1
	.uleb128 0
	.uleb128 0
.LLSDACSE746:
	.text
	.size	__Z6test03ii, .-__Z6test03ii

References:
- [PING] Re: Add const char* constructors for exception classes in <stdexcept>
  - From: Oleg Endo
- Re: [PING] Re: Add const char* constructors for exception classes in <stdexcept>
  - From: Jonathan Wakely
- Re: [PING] Re: Add const char* constructors for exception classes in <stdexcept>
  - From: Oleg Endo
- Re: [PING] Re: Add const char* constructors for exception classes in <stdexcept>
  - From: Jonathan Wakely

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