[llvm-bugs] [Bug 44356] New: [Compile Time] 35% spent in GVN

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Dec 20 09:45:06 PST 2019


            Bug ID: 44356
           Summary: [Compile Time] 35% spent in GVN
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: paulsson at linux.vnet.ibm.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 22957
  --> https://bugs.llvm.org/attachment.cgi?id=22957&action=edit
testcases in compressed tar file

This csmith program is more than 2x compile time than gcc (even with

time gcc -O3: 25s
time clang -O3 -march=z13 crash6.i -o a.out -w -c -mllvm
-disable-phi-elim-edge-splitting -ftime-report
user    1m8.106s
Global Value Numbering 35%

I tried to reduce the test case with creduce, and got about 80% size reduction.
GVN is still dominating the compile time, which is now less than one second.

clang -O3 -march=z13 tc_GVN_CTime.i -o a.out -w -c
user    0m0.784s

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