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
