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LAST BUILD ON BRANCH skaplun/lj-1057-arm64-stp-fusing-across-tbar
branch: skaplun/lj-1057-arm64-stp-fusing-across-tbar
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coverage: 93.064% (+0.04%) from 93.02%
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Buristan 
ARM64: Prevent STP fusion for conditional code emitted by TBAR.

Thanks to Peter Cawley.

(cherry picked from commit 7cc53f0b8)

Assume we have a trace for the several `setmetatable()` calls to the
same table. This trace contains the following IR:
| 0011          p64 FREF   0003  tab.meta
| ...
| 0018 x0    >  tab TNEW   0    0
| 0019          tab TBAR   0003
| 0020          tab FSTORE 0011  0018

The expected mcode to be emitted for the last two IRs is the following:
| 55626cffb0  ldrb  w30, [x19, 8] ; tab->marked
| 55626cffb4  tst   w30, 0x4      ; Is black?
| 55626cffb8  beq   0x626cffd0     ; Skip marking.
| 55626cffbc  ldr   x27, [x20, 128]
| 55626cffc0  and   w30, w30, 0xfffffffb
| 55626cffc4  str   x19, [x20, 128]
| 55626cffcc  strb  w30, [x19, 8]  ; tab->marked
| 55626cffc8  str   x27, [x19, 24] ; tab->gclist
| 55626cffd0  str   x0,  [x19, 32] ; tab->metatable

But the last 2 instructions are fused into the following `stp`:
| 55581dffd0  stp   x27, x0, [x19, 48]
Hence, the GC propagation frontier back is done partially, since
`str x27, [x19, 24]` is not skipped despite TBAR semantics. This leads
to the incorrect value in the `gclist` and the segmentation fault during
its traversal on GC step.

This patch prevents this fusion via switching instruction for
`tab->gclist` and `tab->marked` storing.

Sergey Kaplun:
* added the description and the test for the problem

Part of tarantool/tarantool#11691

5713 of 6047 branches covered (94.48%)

Branch coverage included in aggregate %.

21793 of 23509 relevant lines covered (92.7%)

3874273.86 hits per line

Relevant lines Covered
23509 RELEVANT LINES 21793 COVERED LINES
3874273.86 HITS PER LINE
Source Files on skaplun/lj-1057-arm64-stp-fusing-across-tbar

Recent builds

Builds Branch Commit Type Ran Committer Via Coverage
17261935064 skaplun/lj-1057-arm64-stp-fusing-across-tbar ARM64: Prevent STP fusion for conditional code emitted by TBAR. Thanks to Peter Cawley. (cherry picked from commit 7cc53f0b8) Assume we have a trace for the several `setmetatable()` calls to the same table. This t... push Buristan github
93.06
16491528542 skaplun/lj-1057-arm64-stp-fusing-across-tbar ARM64: Prevent STP fusion for conditional code emitted by TBAR. Thanks to Peter Cawley. (cherry picked from commit 7cc53f0b8) Assume we have a trace for the several `setmetatable()` calls to the same table. This t... push Buristan github
93.02
16467146389 skaplun/lj-1057-arm64-stp-fusing-across-tbar ARM64: Prevent STP fusion for conditional code emitted by TBAR. Thanks to Peter Cawley. (cherry picked from commit 7cc53f0b8) Assume we have a trace for the several `setmetatable()` calls to the same table. This t... push Buristan github
93.06
16223466479 skaplun/lj-1057-arm64-stp-fusing-across-tbar ARM64: Prevent STP fusion for conditional code emitted by TBAR. Thanks to Peter Cawley. (cherry picked from commit 7cc53f0b8) Assume we have a trace for the several `setmetatable()` calls to the same table. This t... push Buristan github
93.06
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