[Flang] Dumping 'flang' type causes a crash

[erichkeane]

See below: I've provided enough backtrace I think to figure out what is going on here, but I'm trying to figure out the type of loweredExpr, but it causes a crash in the getContext.

Args:

(gdb) show args
Argument list to give program being debugged when it is started is "-fc1 -fopenacc flang_parallel_self.f90 -emit-fir -o -".

Soruce of that file is:
https://godbolt.org/z/aaEd4oxWj

(gdb) p loweredExpr.getType().dump()

Program received signal SIGSEGV, Segmentation fault.
mlir::Dialect::getContext (this=0x7fffffff18a8cc) at /local/home/ekeane/llvm-project/flang/../mlir/include/mlir/IR/Dialect.h:52
52        MLIRContext *getContext() const { return context; }   
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on".
Evaluation of the expression containing the function
(mlir::Type::dump() const) will be abandoned.
When the function is done executing, GDB will silently stop.
(gdb) bt
#0  mlir::Dialect::getContext (this=0x7fffffff18a8cc) at /local/home/ekeane/llvm-project/flang/../mlir/include/mlir/IR/Dialect.h:52
#1  0x0000000022628cad in mlir::Type::getContext (this=0x7fffffff17e0) at /local/home/ekeane/llvm-project/mlir/lib/IR/Types.cpp:35
#2  0x00000000223dff6b in mlir::Type::print (this=0x7fffffff17e0, os=...) at /local/home/ekeane/llvm-project/mlir/lib/IR/AsmPrinter.cpp:3968
#3  0x00000000223e0055 in mlir::Type::dump (this=0x7fffffff17e0) at /local/home/ekeane/llvm-project/mlir/lib/IR/AsmPrinter.cpp:3976
#4  <function called from gdb>
#5  Fortran::lower::convertExprToValue (loc=..., converter=..., expr=..., symMap=..., stmtCtx=...) at /local/home/ekeane/llvm-project/flang/lib/Lower/ConvertExprToHLFIR.cpp:2086
#6  0x00000000175fcca7 in (anonymous namespace)::FirConverter::genExprValue (this=0x7fffffff4070, expr=..., context=..., locPtr=0x7fffffff1af8) at /local/home/ekeane/llvm-project/flang/lib/Lower/Bridge.cpp:664
#7  0x000000001817780a in genIfClause (converter=..., clauseLocation=..., ifClause=0x23109b20, ifCond=..., stmtCtx=...) at /local/home/ekeane/llvm-project/flang/lib/Lower/OpenACC.cpp:1690

[llvmbot]

@llvm/issue-subscribers-flang-ir

Author: Erich Keane (erichkeane)

See below: I've provided enough backtrace I think to figure out what is going on here, but I'm trying to figure out the type of `loweredExpr`, but it causes a crash in the `getContext`.

Args:

(gdb) show args
Argument list to give program being debugged when it is started is "-fc1 -fopenacc flang_parallel_self.f90 -emit-fir -o -".

Soruce of that file is:
https://godbolt.org/z/aaEd4oxWj

(gdb) p loweredExpr.getType().dump()

Program received signal SIGSEGV, Segmentation fault.
mlir::Dialect::getContext (this=0x7fffffff18a8cc) at /local/home/ekeane/llvm-project/flang/../mlir/include/mlir/IR/Dialect.h:52
52        MLIRContext *getContext() const { return context; }   
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on".
Evaluation of the expression containing the function
(mlir::Type::dump() const) will be abandoned.
When the function is done executing, GDB will silently stop.
(gdb) bt
#<!-- -->0  mlir::Dialect::getContext (this=0x7fffffff18a8cc) at /local/home/ekeane/llvm-project/flang/../mlir/include/mlir/IR/Dialect.h:52
#<!-- -->1  0x0000000022628cad in mlir::Type::getContext (this=0x7fffffff17e0) at /local/home/ekeane/llvm-project/mlir/lib/IR/Types.cpp:35
#<!-- -->2  0x00000000223dff6b in mlir::Type::print (this=0x7fffffff17e0, os=...) at /local/home/ekeane/llvm-project/mlir/lib/IR/AsmPrinter.cpp:3968
#<!-- -->3  0x00000000223e0055 in mlir::Type::dump (this=0x7fffffff17e0) at /local/home/ekeane/llvm-project/mlir/lib/IR/AsmPrinter.cpp:3976
#<!-- -->4  &lt;function called from gdb&gt;
#<!-- -->5  Fortran::lower::convertExprToValue (loc=..., converter=..., expr=..., symMap=..., stmtCtx=...) at /local/home/ekeane/llvm-project/flang/lib/Lower/ConvertExprToHLFIR.cpp:2086
#<!-- -->6  0x00000000175fcca7 in (anonymous namespace)::FirConverter::genExprValue (this=0x7fffffff4070, expr=..., context=..., locPtr=0x7fffffff1af8) at /local/home/ekeane/llvm-project/flang/lib/Lower/Bridge.cpp:664
#<!-- -->7  0x000000001817780a in genIfClause (converter=..., clauseLocation=..., ifClause=0x23109b20, ifCond=..., stmtCtx=...) at /local/home/ekeane/llvm-project/flang/lib/Lower/OpenACC.cpp:1690

[Leporacanthicus]

Can you check if you do p loweredExpr.getType() that this type isn't nullptr or some similar "this is not valid"?

If it is valid, then there's a real bug, but printing invalid things (e.g. null pointer values) is not expected to work.

[erichkeane]

(gdb) p loweredExpr
$105 = {<hlfir::Entity> = {<mlir::Value> = {impl = 0x231f3240}, <No data fields>}, <No data fields>}
(gdb) p loweredExpr.getType()
$106 = {impl = 0x7fffffff1870}
(gdb) p loweredExpr.dump()
%3:2 = "hlfir.declare"(%arg0, %0) <{fortran_attrs = #fir.var_attrs<intent_in>, operandSegmentSizes = array<i32: 1, 0, 0, 1>, uniq_name = "_QFsquareEx"}> : (!fir.ref<i64>, !fir.dscope) -> (!fir.ref<i64>, !fir.ref<i64>)
$107 = void
(gdb) 

Yep, its valid, see above.

[Leporacanthicus]

Yep, its valid, see above.

Cool, just checking.

Do you have a sample Fortran code and a suitable place for a breakpoint, to reproduce?

[erichkeane]

This was the code I was working through IIRC:

! Type your code here, or load an example.
      integer function square(x)
        implicit none
        integer(8), intent(in) :: x
        !$acc parallel if(x)
        !$acc end parallel
        square = x * x
      end function square

The breakpoint I had was;
Breakpoint 3, genIfClause (converter=..., clauseLocation=..., ifClause=0x23109bc0, ifCond=..., stmtCtx=...) at /local/home/ekeane/llvm-project/flang/lib/Lower/OpenACC.cpp:1689

Which I then stepped into: line 1691 *Fortran::semantics::GetExpr(ifClause->v), stmtCtx, &clauseLocation))

HOWEVER, if you skip to 1692, you can do p cond.getType().dump() to reproduce.