[llvm-bugs] [Bug 37456] New: -time-compilations=N for N > 1 drops data points randomly

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37456

            Bug ID: 37456
           Summary: -time-compilations=N for N > 1 drops data points
                    randomly
           Product: tools
           Version: trunk
          Hardware: PC
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: llc
          Assignee: unassignedbugs at nondot.org
          Reporter: rtereshin at apple.com
                CC: llvm-bugs at lists.llvm.org

-time-compilations=N for N > 1 drops data points randomly

# X86 DAG->DAG Instruction Selection, runs for about 1 ms
> for _ in (seq 20); ./bin/llc -mtriple x86_64-- -O0 ../../test/CodeGen/X86/fast-isel-x86-64.ll -o /dev/null -time-passes -time-compilations=1000 2>&1 | grep -c 'X86 DAG->DAG Instruction Selection'; end
862
885
842
864
865
846
861
874
858
840
865
847
874
853
875
873
859
869
860
876
>

# Fast Register Allocator, runs for about 0.2 ms
> for _ in (seq 20); ./bin/llc -mtriple x86_64-- -O0 ../../test/CodeGen/X86/fast-isel-x86-64.ll -o /dev/null -time-passes -time-compilations=1000 2>&1 | grep -c 'Fast Register Allocator'; end
258
255
233
251
264
254
280
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262
260
276
262
254
271
272
263
260
260
257
279
>

# Rewrite Symbols, runs for unmeasurably small amount of time
> for _ in (seq 20); ./bin/llc -mtriple x86_64-- -O0 ../../test/CodeGen/X86/fast-isel-x86-64.ll -o /dev/null -time-passes -time-compilations=1000 2>&1 | grep -c 'Rewrite Symbols'; end
900
893
884
906
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906
885
899
897
883
909
870
911
900
898
912
892
894
896
908
>

It behaves this way for any input LLVM IR I've tried, big (like sqlite3
amalgamation) and small (like shown above), for any target I've tried (x86-64
and AArch64), and any pass.
Tried on trunk llc as of time of writing (r332192) under macOS on x86-64 iMac.

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