lang.opt: Add -Wdo-subscript.

2017-09-25  Thomas Koenig  <tkoenig@gcc.gnu.org>

	* lang.opt:  Add -Wdo-subscript.
	* frontend-passes.c (do_t): New type.
	(doloop_list): Use variable of do_type.
	(if_level): Variable to track if levels.
	(select_level): Variable to track select levels.
	(gfc_run_passes): Initialize i_level and select_level.
	(doloop_code): Record current level of if + select
	level in doloop_list.  Add seen_goto if there could
	be a branch outside the loop. Use different type for
	doloop_list.
	(doloop_function): Call do_intent and do_subscript; move
	functionality of checking INTENT to do_intent.
	(insert_index_t): New type, for callback_insert_index.
	(callback_insert_index): New function.
	(insert_index): New function.
	(do_subscript): New function.
	(do_intent): New function.
	(gfc_code_walker): Keep track of if_level and select_level.
	* invoke.texi: Document -Wdo-subscript.

2017-09-25  Thomas Koenig  <tkoenig@gcc.gnu.org>

	* gfortran.dg/do_subscript_1.f90: New test.
	* gfortran.dg/do_subscript_2.f90: New test.
	* gfortran.dg/gomp/associate1.f90: Add out of bounds warning.
	* gfortran.dg/predcom-1.f: Adjust loop bounds.
	* gfortran.dg/unconstrained_commons.f: Add out of bounds warning.

From-SVN: r253156

gcc/fortran/ChangeLog

+2017-09-25  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	* lang.opt:  Add -Wdo-subscript.
+	* frontend-passes.c (do_t): New type.
+	(doloop_list): Use variable of do_type.
+	(if_level): Variable to track if levels.
+	(select_level): Variable to track select levels.
+	(gfc_run_passes): Initialize i_level and select_level.
+	(doloop_code): Record current level of if + select
+	level in doloop_list.  Add seen_goto if there could
+	be a branch outside the loop. Use different type for
+	doloop_list.
+	(doloop_function): Call do_intent and do_subscript; move
+	functionality of checking INTENT to do_intent.
+	(insert_index_t): New type, for callback_insert_index.
+	(callback_insert_index): New function.
+	(insert_index): New function.
+	(do_subscript): New function.
+	(do_intent): New function.
+	(gfc_code_walker): Keep track of if_level and select_level.
+	* invoke.texi: Document -Wdo-subscript.
+
 2017-09-25  Janne Blomqvist  <jb@gcc.gnu.org>
 
 	* trans.c (gfc_unlikely): Remove unnecessary fold_convert.

gcc/fortran/invoke.texi

@@ -145,8 +145,8 @@ by type.  Explanations are in the following sections.
 @xref{Error and Warning Options,,Options to request or suppress errors
 and warnings}.
 @gccoptlist{-Waliasing -Wall -Wampersand -Wargument-mismatch -Warray-bounds
--Wc-binding-type -Wcharacter-truncation @gol
--Wconversion -Wfunction-elimination -Wimplicit-interface @gol
+-Wc-binding-type -Wcharacter-truncation -Wconversion @gol
+-Wdo-subscript -Wfunction-elimination -Wimplicit-interface @gol
 -Wimplicit-procedure -Wintrinsic-shadow -Wuse-without-only -Wintrinsics-std @gol
 -Wline-truncation -Wno-align-commons -Wno-tabs -Wreal-q-constant @gol
 -Wsurprising -Wunderflow -Wunused-parameter -Wrealloc-lhs -Wrealloc-lhs-all @gol
@@ -907,8 +907,8 @@ option does @emph{not} imply @option{-Wconversion}.
 @cindex extra warnings
 @cindex warnings, extra
 Enables some warning options for usages of language features which
-may be problematic. This currently includes @option{-Wcompare-reals}
-and @option{-Wunused-parameter}.
+may be problematic. This currently includes @option{-Wcompare-reals},
+@option{-Wunused-parameter} and @option{-Wdo-subscript}.
 
 @item -Wimplicit-interface
 @opindex @code{Wimplicit-interface}
@@ -1080,6 +1080,21 @@ target. This option is implied by @option{-Wall}.
 Warn if a @code{DO} loop is known to execute zero times at compile
 time.  This option is implied by @option{-Wall}.
 
+@item -Wdo-subscript
+@opindex @code{Wdo-subscript}
+Warn if an array subscript inside a DO loop could lead to an
+out-of-bounds access even if the compiler can not prove that the
+statement is actually executed, in cases like
+@smallexample
+  real a(3)
+  do i=1,4
+    if (condition(i)) then
+      a(i) = 1.2
+    end if
+  end do
+@end smallexample
+This option is implied by @option{-Wextra}.
+
 @item -Werror
 @opindex @code{Werror}
 @cindex warnings, to errors

gcc/fortran/lang.opt

@@ -237,6 +237,10 @@ Wconversion-extra
 Fortran Var(warn_conversion_extra) Warning
 Warn about most implicit conversions.
 
+Wdo-subscript
+Fortran Var(warn_do_subscript) Warning LangEnabledBy(Fortran,Wextra)
+Warn about possibly incorrect subscripts in do loops
+
 Wextra
 Fortran Warning
 ; Documented in common

gcc/testsuite/ChangeLog

+2017-09-25  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	* gfortran.dg/do_subscript_1.f90: New test.
+	* gfortran.dg/do_subscript_2.f90: New test.
+	* gfortran.dg/gomp/associate1.f90: Add out of bounds warning.
+	* gfortran.dg/predcom-1.f: Adjust loop bounds.
+	* gfortran.dg/unconstrained_commons.f: Add out of bounds warning.
+
 2017-09-25  Will Schmidt  <will_schmidt@vnet.ibm.com>
 
 	* gcc.target/powerpc/fold-vec-st-char.c: New.

gcc/testsuite/gfortran.dg/do_subscript_1.f90

+! { dg-do compile }
+program main
+  real, dimension(3) :: a
+  a = 42.
+  do i=-1,3,2 ! { dg-warning "out of bounds" }
+     a(i) = 0  ! { dg-warning "out of bounds \\(-1 < 1\\)" }
+  end do
+  do i=4,1,-1 ! { dg-warning "out of bounds" }
+     a(i) = 22 ! { dg-warning "out of bounds \\(4 > 3\\)" }
+  end do
+  do i=1,4 ! { dg-warning "out of bounds" }
+     a(i) = 32 ! { dg-warning "out of bounds \\(4 > 3\\)" }
+  end do
+  do i=3,0,-1 ! { dg-warning "out of bounds" }
+     a(i) = 12 ! { dg-warning "out of bounds \\(0 < 1\\)" }
+  end do
+  do i=-1,3
+     if (i>0) a(i) = a(i) + 1 ! No warning inside if
+  end do
+  do i=-1,4
+     select case(i)
+     case(1:3)
+        a(i) = -234  ! No warning inside select case
+     end select
+  end do
+  do i=1,3 ! { dg-warning "out of bounds" }
+     a(i+1) = a(i) ! { dg-warning "out of bounds \\(4 > 3\\)" }
+     a(i-1) = a(i) ! { dg-warning "out of bounds \\(0 < 1\\)" }
+  end do
+  do i=3,1,-1 ! { dg-warning "out of bounds" }
+     a(i) = a(i-1) ! { dg-warning "out of bounds \\(0 < 1\\)" }
+     a(i) = a(i+1) ! { dg-warning "out of bounds \\(4 > 3\\)" }
+  end do
+  do i=1,2 ! { dg-warning "out of bounds" }
+     a(i) = a(i*i) ! { dg-warning "out of bounds \\(4 > 3\\)" }
+  end do
+  do i=1,4,2
+     a(i) = a(i)*2 ! No error
+  end do
+  do i=1,4
+     if (i > 3) exit
+     a(i) = 33
+  end do
+  do i=0,3 ! { dg-warning "out of bounds \\(0 < 1\\)" }
+    a(i) = 13.  ! { dg-warning "out of bounds \\(0 < 1\\)" }
+    if (i < 1) exit
+  end do
+  do i=0,3
+    if (i < 1) cycle
+    a(i) = -21.
+  end do
+  do i=0,3 ! { dg-warning "out of bounds \\(0 < 1\\)" }
+    do j=1,2
+       a(i) = -123 ! { dg-warning "out of bounds \\(0 < 1\\)" }
+    end do
+  end do
+end program main

gcc/testsuite/gfortran.dg/do_subscript_2.f90

+! { dg-do compile }
+! { dg-additional-options "-Wdo-subscript" }
+program main
+  real, dimension(3) :: a
+  a = 42.
+  do i=-1,3 ! { dg-warning "out of bounds \\(-1 < 1\\)" }
+     select case(i)
+     case(1:3)
+        a(i) = -234  ! { dg-warning "out of bounds \\(-1 < 1\\)" }
+     end select
+  end do
+  do i=1,4,2
+     a(i) = a(i)*2 ! No warning - end value is 3
+  end do
+  do i=1,4  ! { dg-warning "out of bounds \\(4 > 3\\)" }
+     if (i > 3) exit
+     a(i) = 33  ! { dg-warning "out of bounds \\(4 > 3\\)" }
+  end do
+  do i=0,3  ! { dg-warning "out of bounds \\(0 < 1\\)" }
+    if (i < 1) cycle
+    a(i) = -21. ! { dg-warning "out of bounds \\(0 < 1\\)" }
+  end do
+end program main