[PATCH] D89476: [llc] Use -filetype=null to disable MIR printing

[Jay Foad via Phabricator via llvm-commits]

foad added inline comments.


================
Comment at: llvm/lib/CodeGen/LLVMTargetMachine.cpp:203
+  } else {
+    // The Null output is intended for use for performance analysis and testing,
+    // not real users.
----------------
MaskRay wrote:
> Just say createPrintMIRPass is redundant for null output?
> 
> How much overhead have you measured?
> How much overhead have you measured?

More than 50% in MIR printing in cases like this:

```
$ ~/llvm-release/bin/llc -march=aarch64 sqlite3.bc -filetype=null -stop-after=finalize-isel -time-passes > /dev/null
===-------------------------------------------------------------------------===
                      ... Pass execution timing report ...
===-------------------------------------------------------------------------===
  Total Execution Time: 4.7993 seconds (4.8033 wall clock)

   ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
   2.5278 ( 54.2%)   0.0577 ( 42.8%)   2.5856 ( 53.9%)   2.5887 ( 53.9%)  MIR Printing Pass
   1.3541 ( 29.0%)   0.0530 ( 39.3%)   1.4071 ( 29.3%)   1.4081 ( 29.3%)  AArch64 Instruction Selection
   0.1636 (  3.5%)   0.0024 (  1.8%)   0.1660 (  3.5%)   0.1661 (  3.5%)  CodeGen Prepare
...
```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D89476/new/

https://reviews.llvm.org/D89476