[LLVMbugs] [Bug 22065] New: Optimize 0>=p-q to q >= p for char*p,*q;

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22065

            Bug ID: 22065
           Summary: Optimize   0>=p-q   to   q >= p  for char*p,*q;
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: llvmbugs at contacts.eelis.net
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

It was noticed that Boost's iterator_facade incurred a performance penalty
(while it should ideally be zero-overhead), which results from the fact that
Clang does not optimize   0>=p-q  to  q>=p  for char*p,*q;. See attachment.

Chandler was reported as saying it's a case of a missing InstCombine rule.

This probably applies to > and < and <= as well.

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