[PATCH] D91217: [flang] Allow labels on END statements.

[Peter Klausler via Phabricator via llvm-commits]

klausler created this revision.
klausler added a reviewer: PeteSteinfeld.
klausler added a project: Flang.
Herald added subscribers: llvm-commits, jdoerfert.
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  F18 clause 5.3.3 explicitly allows labels on program unit END statements.
  Label resolution code accounts for this for singleton program units,
  but incorrectly generates an error for host subprograms with internal
  subprograms.
  
     subroutine s(n)
        call s1(n)
        if (n == 0) goto 88 ! incorrect error
        print*, 's'
     contains
        subroutine s1(n)
           if (n == 0) goto 77 ! ok
           print*, 's1'
     77 end subroutine s1
     88 end
  
  Label resolution code makes a sequential pass over an entire file to
  collect label information for all subprograms, followed by a pass through
  that information for semantics checks.  The problem is that END statements
  may be separated from prior subprogram code by internal subprogram
  definitions, so an END label can be associated with the wrong subprogram.
  
  There are several ways to fix this.  Labels are always local to a
  subprogram.  So the two separate passes over the entire file could probably
  instead be interleaved to perform analysis on a subprogram as soon as the
  end of the subprogram is reached, using a small stack.  The stack structure
  would account for the "split" code case.  This might work.
  
  It is possible that there is some not otherwise apparent advantage to
  the current full-file pass design.  The parse tree has productions that
  provide access to a subprogram END statement "in advance".  An alternative
  is to access this information to solve the problem.  This PR implements
  this latter option.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D91217

Files:
  flang/lib/Semantics/resolve-labels.cpp
  flang/test/Semantics/label15.f90
  flang/test/Semantics/label16.f90

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