[llvm-bugs] [Bug 37762] New: [X86] Use SelectionDAG::computeOverflowKind to relax ADD/SUB S/US nodes to generic ADD/SUB

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37762

            Bug ID: 37762
           Summary: [X86] Use SelectionDAG::computeOverflowKind to relax
                    ADD/SUB S/US nodes to generic ADD/SUB
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: craig.topper at gmail.com, deadalnix at gmail.com,
                    lebedev.ri at gmail.com, llvm-bugs at lists.llvm.org,
                    spatel+llvm at rotateright.com

If the saturated nodes are guaranteed not to overflow then they should become
generic ADD/SUB nodes. As a stretch goal the HADDS/HSUBS cases could be handled
as well.

Many CPUs can perform the saturated forms only on some ports, or at a lower
perf.

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