rustc_platform_intrinsics takes LLVM lots of time to compile

[arielb1]

CPU:

model name  : Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz
stepping    : 3
microcode   : 0x12
cpu MHz     : 3392.293
cache size  : 8192 KB

with debuginfo:

time: 0.580; rss: 228MB translation
  time: 0.228; rss: 172MB       llvm function passes
  time: 48.802; rss: 287MB      llvm module passes
  time: 17.807; rss: 454MB      codegen passes
  time: 0.001; rss: 454MB       codegen passes
time: 67.451; rss: 454MB        LLVM passes

without debuginfo:

time: 0.467; rss: 221MB translation
  time: 0.179; rss: 167MB       llvm function passes
  time: 30.995; rss: 222MB      llvm module passes
  time: 10.347; rss: 342MB      codegen passes
  time: 0.000; rss: 342MB       codegen passes
time: 41.762; rss: 342MB        LLVM passes

We should either make this fast or write it to not trigger this worst-case.

cc @huonw
cc @dotdash

there was also a case of 600s compile-time on the same CPU, but I can't reproduce it.

[dotdash]

We have a winner here:

  161.8920 ( 66.8%)   0.0340 (  4.9%)  161.9260 ( 66.6%)  161.6847 ( 66.6%)  Function Integration/Inlining
   8.2570 (  3.4%)   0.0270 (  3.9%)   8.2840 (  3.4%)   8.2553 (  3.4%)  Induction Variable Simplification
   6.8030 (  2.8%)   0.0100 (  1.4%)   6.8130 (  2.8%)   6.7934 (  2.8%)  Induction Variable Users

That's pretty impressive...

[arielb1]

what command did you use?

[dotdash]

That's with -Ztime-llvm-passes

[dotdash]

Findings so far: This is caused by LLVM doing cost analysis on the caller if the caller has local linkage.

[dotdash]

Marking the three find() functions as #[inline(never)] stops us from triggering a pathological case in the inliner and reduces compile times by almost 70%.