| Issue |
55395
|
| Summary |
[IROutliner] MultiSource/Benchmarks/MiBench/network-patricia is larger with IR outliner enabled
|
| Labels |
backend:AArch64,
llvm:optimizations,
llvm:codesize
|
| Assignees |
|
| Reporter |
ornata
|
Compiling for AArch64.
-Oz = 5.86% bigger with outliner
-O2 = 6.78% bigger with outliner
(To be fair this is a tiny benchmark)
This was done by compiling the LLVM test suite using LNT and looking at the `size.__text` results.
# Reproducing
The IR for the worst size-increased file in network-patricia @ -O2 is here: https://godbolt.org/z/KGfEaMafb
Compiling this to assembly and using asm-printer remarks...
```
$ ~/llvm-project/build/bin/clang -S -O2 -Rpass-analysis=asm-printer /tmp/patricia-stripped.ll -o /dev/null
remark: <unknown>:0:0: 128 instructions in function [-Rpass-analysis=asm-printer]
$ ~/llvm-project/build/bin/clang -S -O2 -Rpass-analysis=asm-printer -mllvm -ir-outliner /tmp/patricia-stripped.ll -o /dev/null
remark: <unknown>:0:0: 144 instructions in function [-Rpass-analysis=asm-printer]
remark: <unknown>:0:0: 6 instructions in function [-Rpass-analysis=asm-printer]
remark: <unknown>:0:0: 5 instructions in function [-Rpass-analysis=asm-printer]
```
Baseline: 128 instructions
Outliner: 155 instructions
I think there are a couple issues here, one of them probably reduces down to this: https://godbolt.org/z/Pfq8oK68P
```
$ ~/llvm-project/build/bin/clang -S -O2 -Rpass-analysis=asm-printer /tmp/test.ll -o /dev/null
remark: <unknown>:0:0: 7 instructions in function [-Rpass-analysis=asm-printer]
remark: <unknown>:0:0: 7 instructions in function [-Rpass-analysis=asm-printer]
$ ~/llvm-project/build/bin/clang -S -O2 -mllvm -ir-outliner -Rpass-analysis=asm-printer /tmp/test.ll -o /dev/null
remark: <unknown>:0:0: 4 instructions in function [-Rpass-analysis=asm-printer]
remark: <unknown>:0:0: 4 instructions in function [-Rpass-analysis=asm-printer]
remark: <unknown>:0:0: 7 instructions in function [-Rpass-analysis=asm-printer]
```
Baseline: 14 instructions total
Outliner: 15 instructions total
# Analysis
Using `llvm-remark-size-diff` on network-patricia at -O2, we can see that the only difference is that main increased by 13 instructions, and two outlined functions were added.
```
++ > outlined_ir_func_0, 5 instrs, 0 stack B
++ > outlined_ir_func_1, 5 instrs, 0 stack B
== > main, 13 instrs, 0 stack B
### Summary ###
Total change:
instruction count: 23 (6.78%)
stack byte usage: None
```
Then I just recompiled with `clang -save-temps` and yoinked out the bitcode.
cc @AndrewLitteken
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