[llvm-bugs] [Bug 35732] New: [DAGCombiner] Remove reduceBuildVecConvertToConvertBuildVec and rely on the vectorizers instead

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35732

            Bug ID: 35732
           Summary: [DAGCombiner] Remove
                    reduceBuildVecConvertToConvertBuildVec and rely on the
                    vectorizers instead
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: efriedma at codeaurora.org, hfinkel at anl.gov,
                    llvm-bugs at lists.llvm.org, michael.hliao at gmail.com,
                    spatel+llvm at rotateright.com

reduceBuildVecConvertToConvertBuildVec vectorizes int2float in the DAGCombiner,
which means that even if the LV/SLP has decided to keep scalar code, this will
override this.

While there are cases where vectorization is necessary in the DAG (mainly due
to legalization artefacts), I don't think this is the case here. I think we
should get rid of this and instead assume that the vectorizers know what they
are doing. 

SVN blame says this code was added back in 2012.

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