[llvm-branch-commits] [flang] [flang] Do not branch to a FORMAT statement from an assigned GO TO (PR #217220)

[Kareem Ergawy via llvm-branch-commits]

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@@ -0,0 +1,75 @@
+! RUN: bbc -emit-fir -o - %s | FileCheck %s
+
+! A FORMAT statement is not a branch target.  Branching to a label that was
+! ASSIGN'd from one is not conforming, and the program is meant to reach the
+! run-time error rather than jump into the FORMAT statement.
+
+! The only label assigned to j is a FORMAT, so no target survives and no
+! branch is generated at all.
+! CHECK-LABEL: func.func @_QPfmt_only(
+! CHECK:         %[[J:.*]] = fir.declare %arg0
+! CHECK:         fir.store %c1{{.*}} to %[[J]]
+! CHECK-NOT:     fir.select
+! CHECK-NOT:     ^bb
+! CHECK:         fir.call @_FortranAReportFatalUserError
+! CHECK-NEXT:    fir.unreachable
+subroutine fmt_only(j)
+  integer :: j
+  assign 1 to j
+  go to j
+1 format("fmt")
+end subroutine
+
+! Both labels are assigned to j, but only 20 is a branch target.  The select
+! carries exactly one case, for 20; label 1 does not appear.
+! CHECK-LABEL: func.func @_QPfmt_and_real(
+! CHECK:         %[[J:.*]] = fir.declare %arg0
+! CHECK:         fir.store %c1{{.*}} to %[[J]]
+! CHECK:         fir.store %c20{{.*}} to %[[J]]
+! CHECK:         %[[V:.*]] = fir.load %[[J]]
+! CHECK:         fir.select %[[V]] : i32 [20, ^bb[[TGT:[0-9]+]], unit, ^bb[[ERR:[0-9]+]]]
+!
+! The default destination reports the error and terminates.
+! CHECK:       ^bb[[ERR]]:
+! CHECK:         fir.call @_FortranAReportFatalUserError
+! CHECK-NEXT:    fir.unreachable
+!
+! The one real target is the PRINT at label 20, which returns normally.
+! CHECK:       ^bb[[TGT]]:
+! CHECK:         fir.call @_FortranAioBeginExternalListOutput
+! CHECK:         return
+subroutine fmt_and_real(j)
+  integer :: j
+  assign 1 to j
+  assign 20 to j
+  go to j
+1 format("fmt")
+20 print *, "twenty"
+end subroutine
+
+! FORMAT is the only labelled statement that can be assigned and then reach the
+! GO TO without being a branch target; every other kind is rejected by semantic
+! analysis at the ASSIGN.  The labels below are branch targets of four different
+! kinds -- an action statement, the statement that begins an IF construct, the
+! statement that begins a DO construct, and the END statement of the subroutine
+! -- so every one of them survives and appears as a case of the select.  Each is
+! branched to from the same inclusive scope, and the two construct labels name
+! the statement that begins the construct rather than the one that ends it, so
+! control enters the construct normally instead of jumping into its interior.
+! CHECK-LABEL: func.func @_QPbranch_target_kinds(
+! CHECK:         fir.select %{{.*}} : i32 [10, ^bb{{[0-9]+}}, 20, ^bb{{[0-9]+}}, 30, ^bb{{[0-9]+}}, 40, ^bb{{[0-9]+}}, unit, ^bb{{[0-9]+}}]
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ergawy wrote:

Done in 6d3274b48ed580f1a759895bfea11694af4cb719.

https://github.com/llvm/llvm-project/pull/217220