[llvm-bugs] [Bug 44518] New: very slow compilation at -O2 and -O3

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44518

            Bug ID: 44518
           Summary: very slow compilation at -O2 and -O3
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: hehaochen13 at nudt.edu.cn
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Created attachment 23010
  --> https://bugs.llvm.org/attachment.cgi?id=23010&action=edit
Test case for linux

clang 3.4.2:
  g++ -O0 -c t2.cc  1.1s
  g++ -O1 -c t2.cc  5.0s
  g++ -O2 -c t2.cc 1m 21s
  g++ -O3 -c t2.cc 1m 25s

---User Time---  --System Time--  --User+System--  ---Wall Time---  --- Name
---
42.2165 ( 51.7%) 2.5971 ( 48.9%)  44.8135 (51.6%)  44.8155 (51.6%) Value
Propagation
27.8303 ( 34.1%) 1.8011 ( 33.9%)  29.6314 (34.1%)  29.6327 (34.1%) Value
Propagation


apple clang 11.0:
  g++ -O0 -c t2.cc  1.0s
  g++ -O1 -c t2.cc  2.9s
  g++ -O2 -c t2.cc 36.5s
  g++ -O3 -c t2.cc 35.8s
---User Time--- --System Time-- --User+System-- ---Wall Time---  --- Name ---
23.6581 (64.7%) 0.1341 (19.8%)  23.7922 (63.9%) 23.9388 (64.0%) Global Value
Numbering
5.8555 (16.0%)  0.0067 ( 1.0%)   5.8622 (15.7%)  5.8636 (15.7%) Hot Cold
Splitting


But in gcc-4.8.5:
  g++ -O0 -c t2.cc  1.7s
  g++ -O1 -c t2.cc  3.0s
  g++ -O2 -c t2.cc  3.8s
  g++ -O3 -c t2.cc  3.9s

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