PR modula2/110125 variables reported as uninitialized when set inside WITH

The modula-2 static analysis incorrectly identifies variables as
uninitialized if they are initialized within a WITH statement.  This bug
fix re-implements the variable static analysis and will detect simple
pointer record fields being accessed before being initialized.
The static analysis is limited to the first basic block in a procedure.
It does not check variant records, arrays or sets.  A new option
-Wuninit-variable-checking will turn on the new semantic checking
(-Wall also enables the new checking).

gcc/ChangeLog:

	PR modula2/110125
	* doc/gm2.texi (Semantic checking): Include examples using
	-Wuninit-variable-checking.

gcc/m2/ChangeLog:

	PR modula2/110125
	* Make-lang.in (GM2-COMP-BOOT-DEFS): Add M2SymInit.def.
	(GM2-COMP-BOOT-MODS): Add M2SymInit.mod.
	* gm2-compiler/M2BasicBlock.mod: Formatting changes.
	* gm2-compiler/M2Code.mod: Remove import of VariableAnalysis from
	M2Quads.  Import VariableAnalysis from M2SymInit.mod.
	* gm2-compiler/M2GCCDeclare.mod (PrintVerboseFromList):
	Add debugging print for a component.
	(TypeConstFullyDeclared): Call RememberType for every type.
	* gm2-compiler/M2GenGCC.mod (CodeReturnValue): Add parameter to
	GetQuadOtok.
	(CodeBecomes): Add parameter to GetQuadOtok.
	(CodeXIndr): Add parameter to GetQuadOtok.
	* gm2-compiler/M2Optimize.mod (ReduceBranch): Reformat and
	preserve operand token positions when reducing the branch
	quadruples.
	(ReduceGoto): Reformat.
	(FoldMultipleGoto): Reformat.
	(KnownReachable): Reformat.
	* gm2-compiler/M2Options.def (UninitVariableChecking): New
	variable declared and exported.
	(SetUninitVariableChecking): New procedure.
	* gm2-compiler/M2Options.mod (SetWall): Set
	UninitVariableChecking.
	(SetUninitVariableChecking): New procedure.
	* gm2-compiler/M2Quads.def (PutQuadOtok): Exported and declared.
	(VariableAnalysis): Removed.
	* gm2-compiler/M2Quads.mod (PutQuadOtok): New procedure.
	(doVal): Reformatted.
	(MarkAsWrite): Reformatted.
	(MarkArrayAsWritten): Reformatted.
	(doIndrX): Use PutQuadOtok.
	(MakeRightValue): Use GenQuadOtok.
	(MakeLeftValue): Use GenQuadOtok.
	(CheckReadBeforeInitialized): Remove.
	(IsNeverAltered): Reformat.
	(DebugLocation): New procedure.
	(BuildDesignatorPointer): Use GenQuadO to preserve operand token
	position.
	(BuildRelOp): Use GenQuadOtok ditto.
	* gm2-compiler/SymbolTable.def (VarCheckReadInit): New procedure.
	(VarInitState): New procedure.
	(PutVarInitialized): New procedure.
	(PutVarFieldInitialized): New procedure function.
	(GetVarFieldInitialized): New procedure function.
	(PrintInitialized): New procedure.
	* gm2-compiler/SymbolTable.mod (VarCheckReadInit): New procedure.
	(VarInitState): New procedure.
	(PutVarInitialized): New procedure.
	(PutVarFieldInitialized): New procedure function.
	(GetVarFieldInitialized): New procedure function.
	(PrintInitialized): New procedure.
	(LRInitDesc): New type.
	(SymVar): InitState new field.
	(MakeVar): Initialize InitState.
	* gm2-gcc/m2options.h (M2Options_SetUninitVariableChecking):
	New function declaration.
	* gm2-lang.cc (gm2_langhook_handle_option): Detect
	OPT_Wuninit_variable_checking and call SetUninitVariableChecking.
	* lang.opt: Add Wuninit-variable-checking.
	* gm2-compiler/M2SymInit.def: New file.
	* gm2-compiler/M2SymInit.mod: New file.

gcc/testsuite/ChangeLog:

	PR modula2/110125
	* gm2/switches/uninit-variable-checking/fail/testinit.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testlarge.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testlarge2.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testrecinit.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testrecinit2.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testrecinit5.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testsmallrec.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testsmallrec2.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testsmallvec.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testvarinit.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testwithnoptr.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testwithptr.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testwithptr2.mod: New test.
	* gm2/switches/uninit-variable-checking/fail/testwithptr3.mod: New test.
	* gm2/switches/uninit-variable-checking/pass/testrecinit3.mod: New test.
	* gm2/switches/uninit-variable-checking/pass/testrecinit5.mod: New test.
	* gm2/switches/uninit-variable-checking/pass/testsmallrec.mod: New test.
	* gm2/switches/uninit-variable-checking/pass/testsmallrec2.mod: New test.
	* gm2/switches/uninit-variable-checking/pass/testvarinit.mod: New test.
	* gm2/switches/uninit-variable-checking/pass/testwithptr.mod: New test.
	* gm2/switches/uninit-variable-checking/pass/testwithptr2.mod: New test.
	* gm2/switches/uninit-variable-checking/pass/testwithptr3.mod: New test.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>

1 files changed, 126 insertions, 0 deletions

diff --git a/gcc/doc/gm2.texi b/gcc/doc/gm2.texi
index 3e531a8..ae87434 100644
--- a/gcc/doc/gm2.texi
+++ b/gcc/doc/gm2.texi
@@ -659,6 +659,11 @@ zero.
 @item -fwholevalue
 generate code to detect whole number overflow and underflow.
 
+@item -Wuninit-variable-checking
+issue a warning if a variable is used before it is initialized.
+The checking only occurs in the first basic block in each procedure.
+It does not check parameters, array types or set types.
+
 @c the following warning options are complete but need to be
 @c regression tested against all other front ends
 @c to ensure the options do not conflict.
@@ -1452,6 +1457,127 @@ with @samp{-fsoft-check-all} so that the compiler is able to run the
 optimizer and perform variable and flow analysis before the semantic
 plugin is invoked.
 
+The @samp{-Wuninit-variable-checking} can be used to identify
+uninitialized variables within the first basic block in a procedure.
+The checking is limited to variables so long as they are
+not an array or set or a variant record.
+
+The following example detects whether a sub component within a record
+is uninitialized.
+
+@example
+MODULE testlarge2 ;
+
+TYPE
+   color = RECORD
+              r, g, b: CARDINAL ;
+           END ;
+
+   pixel = RECORD
+              fg, bg: color ;
+           END ;
+
+PROCEDURE test ;
+VAR
+   p: pixel ;
+BEGIN
+   p.fg.r := 1 ;
+   p.fg.g := 2 ;
+   p.fg.g := 3 ;   (* Deliberate typo should be p.fg.b.  *)
+   p.bg := p.fg ;  (* Accessing an uninitialized field.  *)
+END test ;
+
+BEGIN
+   test
+END testlarge2.
+@end example
+
+@example
+$ gm2 -c -Wuninit-variable-checking testlarge2.mod
+testlarge2.mod:19:13: warning: In procedure ‘test’: attempting to
+access expression before it has been initialized
+   19 |    p.bg := p.fg ;  (* Accessing an uninitialized field.  *)
+      |            ~^~~
+@end example
+
+The following example detects if an individual field is uninitialized.
+
+@example
+MODULE testwithnoptr ;
+
+TYPE
+   Vec =  RECORD
+             x, y: CARDINAL ;
+          END ;
+
+PROCEDURE test ;
+VAR
+   p: Vec ;
+BEGIN
+   WITH p DO
+      x := 1 ;
+      x := 2   (* Deliberate typo, user meant y.  *)
+   END ;
+   IF p.y = 2
+   THEN
+   END
+END test ;
+
+BEGIN
+   test
+END testwithnoptr.
+@end example
+
+The following example detects a record is uninitialized via a
+pointer variable in a @samp{WITH} block.
+
+@example
+$ gm2 -g -c -Wuninit-variable-checking testwithnoptr.mod
+testwithnoptr.mod:21:8: warning: In procedure ‘test’: attempting to
+access expression before it has been initialized
+   21 |    IF p.y = 2
+      |       ~^~
+@end example
+
+@example
+MODULE testwithptr ;
+
+FROM SYSTEM IMPORT ADR ;
+
+TYPE
+   PtrToVec = POINTER TO Vec ;
+   Vec = RECORD
+            x, y: CARDINAL ;
+         END ;
+
+PROCEDURE test ;
+VAR
+   p: PtrToVec ;
+   v: Vec ;
+BEGIN
+   p := ADR (v) ;
+   WITH p^ DO
+      x := 1 ;
+      x := 2   (* Deliberate typo, user meant y.  *)
+   END ;
+   IF p^.y = 2
+   THEN
+   END
+END test ;
+
+BEGIN
+   test
+END testwithptr.
+@end example
+
+@example
+gm2 -c -Wuninit-variable-checking testwithptr.mod
+testwithptr.mod:26:9: warning: In procedure ‘test’: attempting to
+access expression before it has been initialized
+   26 |    IF p^.y = 2
+      |       ~~^~
+@end example
+
 @node Extensions, Type compatibility, Semantic checking, Using
 @section GNU Modula-2 language extensions