[Mono-dev] Some strange behavior of optimization options for JIT

[Sergey Tikhonov]

Hello,

I am experiencing some strange problems when run mini tests with
--optimize=all option. Here is example:
method to IR System.Collections.ArrayList:Add (object)
converting (in B2: stack: 0) IL_0000: ldarg.0
converting (in B2: stack: 1) IL_0001: ldfld     0x04000412
converting (in B2: stack: 1) IL_0006: ldlen
converting (in B2: stack: 1) IL_0007: conv.i4
converting (in B2: stack: 1) IL_0008: ldarg.0
converting (in B2: stack: 2) IL_0009: ldfld     0x04000411
converting (in B2: stack: 2) IL_000e: bgt       IL_0021
converting (in B5: stack: 0) IL_0013: ldarg.0
converting (in B5: stack: 1) IL_0014: ldarg.0
converting (in B5: stack: 2) IL_0015: ldfld     0x04000411
converting (in B5: stack: 2) IL_001a: ldc.i4.1
converting (in B5: stack: 3) IL_001b: add
converting (in B5: stack: 2) IL_001c: call      0x06001445
mono_arch_get_inst_for_method: EnsureCapacity
ALPHA: Will call Managed method with 1(1) params. RetType:
MONO_TYPE_VOID(0x1)
ALPHA: Param[0] - simple
ALPHA: Param[1] - simple
converting (in B4: stack: 0) IL_0021: ldarg.0
converting (in B4: stack: 1) IL_0022: ldfld     0x04000412

Here is IR before optimizations:

SSAPRE STARTS PROCESSING METHOD System.Collections.ArrayList:Add
(object)
BEFORE SSAPRE START
CODE BLOCK 3 (nesting 0):
 (stind.i4 local[2] iconst[0])
 (bgt[B6B5] (compare (long_conv_to_i4 (ldlen (ldind.ref (long_add
(ldind.i arg[0]) iconst[24])))) (ldind.i4 (long_add (ldind.i arg[0])
iconst[16]))))
CODE BLOCK 5 (nesting 0):
 (outarg_reg (add (ldind.i4 (long_add (ldind.i arg[0]) iconst[16]))
iconst[1]))
 (outarg_reg (ldind.i arg[0]))
 voidcall[EnsureCapacity]
 br[B4]
CODE BLOCK 4 (nesting 0):

Here is after optimizations:
SSAPRE ENDS PROCESSING METHOD System.Collections.ArrayList:Add (object)
remove_block_if_useless System.Collections.ArrayList:Add (object),
removed BB6
br removal triggered 5 -> 4
BEFORE DECOMPSE START
CODE BLOCK 3 (nesting 0):
 (stind.i4 local[2] iconst[0])
 (stind.i local[9] (long_add (ldind.i arg[0]) iconst[16]))
 (stind.i local[8] (long_add (ldind.i arg[0]) iconst[24]))
 (bgt[B4B5] (compare (long_conv_to_i4 (ldlen (ldind.ref (ldind.i
local[8])))) (ldind.i4 (ldind.i local[9]))))
CODE BLOCK 5 (nesting 0):
 (outarg_reg (add (ldind.i4 (ldind.i local[9])) iconst[1]))
 (outarg_reg (ldind.i arg[0]))
 voidcall[EnsureCapacity]
 nop
CODE BLOCK 4 (nesting 0):

As we see two locals were introduced to hold "sum" results. In
"mono_arch_allocate_vars" the "mono_allocate_stack_slots_full" is called
to allocate locals and calculate offsets for them. Somehow it doesn't do
it:
ALPHA: Locals start offset is 16(10)
ALPHA: Locals size is 24(18)
ALPHA: allocated local 2 to  regoffset[0x1c(alpha_r15)]
ALPHA: allocated local 3 to  regoffset[0x18(alpha_r15)]
ALPHA: allocated local 4 to  regoffset[0x10(alpha_r15)]
ALPHA: allocated local 8 to  regoffset[0x20(alpha_r15)]
ALPHA: allocated local 9 to  regoffset[0x20(alpha_r15)]
ALPHA: allocated local 11 to  regoffset[0x20(alpha_r15)]
ALPHA: reg_save_area_offset at 40(28)
ALPHA: args_save_area_offset at 40(28)
ALPHA: Stack size is 56(38)
DUMP BLOCK 0:
DUMP BLOCK 3:
 (stind.i4 regoffset[0x1c(alpha_r15)] iconst[0])
 (stind.i regoffset[0x20(alpha_r15)] (long_add (ldind.i
regoffset[0x28(alpha_r15)]) iconst[16]))
 (stind.i regoffset[0x20(alpha_r15)] (long_add (ldind.i
regoffset[0x28(alpha_r15)]) iconst[24]))
 (bgt[B4B5] (compare (long_conv_to_i4 (ldlen (ldind.ref (ldind.i
regoffset[0x20(alpha_r15)])))) (ldind.i4 (ldind.i
regoffset[0x20(alpha_r15)]))))
DUMP BLOCK 5:

The local vars 8,9,11 are in the list of local vars, but assigned
offsets are the same. And size allocated for locals is less than
needed. :(

I checked the other arch sources and don't see any magic I have to do.
Any hints? I guess it should allocate it.

Thank you,

Sergey Tikhonov

Head, R&D department
Solvo Ltd.
Saint-Petersburg, Russia
http://www.solvo.ru
tsv at solvo.ru