[SR-14532] 9x regression in compilation time of large classes in Swift 5.4

[kylebshr]

Previous ID	SR-14532
Radar	rdar://problem/77217125
Original Reporter	@kylebshr
Type	Bug
Status	Resolved
Resolution	Done

Attachment: Download

Environment

Swift 5.4 / Xcode 12.5 / MacBook Pro (15-inch, 2019) 2.4 GHz 8-Core Intel Core i9

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 21019f6eabe58038bcaec8824ea2ecfb

Issue Description:

We have a generated class in our code base with over 3,000 properties, which took a long but somewhat reasonable time to compile in Swift <= 5.3.2. With the release of Swift 5.4 we noticed a huge increase in compile time for our project.

I reduced the repro case to a simple class with 3,000 Int properties, and an init that sets each of those properties, similar to our generated code. Compiling this file takes ~139s with Swift 5.3.2 and ~1278s with Swift 5.4 - nearly a 10x slow down.

➜  huge_class swiftc -v
Apple Swift version 5.3.2 (swiftlang-1200.0.45 clang-1200.0.32.28)
Target: x86_64-apple-darwin20.3.0
➜  huge_class swiftc -driver-time-compilation main.swift
===-------------------------------------------------------------------------===
                            Driver Compilation Time
===-------------------------------------------------------------------------===
  Total Execution Time: 0.0002 seconds (139.6951 wall clock)

   ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
   0.0000 ( 60.6%)   0.0000 ( 36.3%)   0.0001 ( 46.2%)  139.4823 ( 99.8%)  {compile: main-9f2913.o <= main.swift}
   0.0000 ( 39.4%)   0.0001 ( 63.7%)   0.0001 ( 53.8%)   0.2128 (  0.2%)  {link: main <= main-9f2913.o}
   0.0001 (100.0%)   0.0001 (100.0%)   0.0002 (100.0%)  139.6951 (100.0%)  Total

➜  huge_class sudo xcode-select -s /Applications/Xcode.app      
Password:
➜  huge_class swiftc -v                                 
Apple Swift version 5.4 (swiftlang-1205.0.26.9 clang-1205.0.19.55)
Target: x86_64-apple-darwin20.3.0
➜  huge_class swiftc -v
Apple Swift version 5.4 (swiftlang-1205.0.26.9 clang-1205.0.19.55)
Target: x86_64-apple-darwin20.3.0
➜  huge_class swiftc -driver-time-compilation main.swift  
===-------------------------------------------------------------------------===
                            Driver Compilation Time
===-------------------------------------------------------------------------===
  Total Execution Time: 0.0001 seconds (1278.5112 wall clock)

   ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
   0.0000 ( 74.0%)   0.0000 ( 50.8%)   0.0001 ( 61.1%)  1278.2003 (100.0%)  {compile: main-018ae1.o <= main.swift}
   0.0000 ( 26.0%)   0.0000 ( 49.2%)   0.0000 ( 38.9%)   0.3109 (  0.0%)  {link: main <= main-018ae1.o}
   0.0000 (100.0%)   0.0001 (100.0%)   0.0001 (100.0%)  1278.5112 (100.0%)  Total

[kylebshr]

I'd like to note that it seems like the slowdown is exponential as you add properties. 100 properties takes 0.24s, 200: 0.45s, 400: 2.01s and 800: 16s.

[rintaro]

@swift-ci create

[rjmccall]

There's a lot more we could do to speed up this test case, but I fixed the biggest problem in #37328

[kylebshr]

Awesome, thank you @rjmccall!