[llvm-bugs] [Bug 34245] New: In case of -ffast-math, the Loop Vectorizer can generate mis-optimized code

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=34245

            Bug ID: 34245
           Summary: In case of  -ffast-math, the Loop Vectorizer can
                    generate mis-optimized code
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: gareevroman at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 19009
  --> https://bugs.llvm.org/attachment.cgi?id=19009&action=edit
Code generated using the -ffast-math option.

In case of  -ffast-math, the Loop Vectorizer can generate mis-optimized code.

For example, in case of "opt without-ffast-math.ll -loop-vectorize -S", I get
without-ffast-math-result.ll, which contains 478 lines of code.

However,, if I run "opt with-ffast-math.ll -loop-vectorize -S", I get
with-ffast-math-result.ll, which contains 1432 lines of code and leads to
execution time regression.

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