[gcc r14-10166] [PATCH] PR modula2/114929 for loop fails to iterate down to zero

Gaius Mulley gaius@gcc.gnu.org
Fri May 3 21:59:13 GMT 2024


https://gcc.gnu.org/g:d811080341adf9d805e3f79a8fd9be2e13bd9848

commit r14-10166-gd811080341adf9d805e3f79a8fd9be2e13bd9848
Author: Gaius Mulley <gaiusmod2@gmail.com>
Date:   Fri May 3 22:58:11 2024 +0100

    [PATCH] PR modula2/114929 for loop fails to iterate down to zero
    
    There is a bug in the for loop control code which is exposed when an
    unsigned type is used in the iterator variable.  See
    gm2/pim/run/pass/testforloopzero[234].mod.  The bug is in the
    calculation of the last iterator value.  The bug fix is to avoid using
    negative expressions when calculating the last iterator value with a
    negative step value.  This patch detects if e1, e2, step value are all
    constant, in which case the ztype is used internally and there is no
    overflow.  If the last iterator value is held in a variable then it
    uses a different method to calculate the last iterator depending upon
    the sign of the step value.
    
    gcc/m2/ChangeLog:
    
            PR modula2/114929
            * gm2-compiler/M2Quads.mod (ForLoopLastIteratorVariable): New
            procedure.
            (ForLoopLastIteratorConstant): Ditto.
            (ForLoopLastIterator): Ditto.
            (BuildForToByDo): Remove LastIterator calculation and call
            ForLoopLastIterator instead.
            (FinalValue): Replace with ...
            (LastIterator): ... this.
    
    gcc/testsuite/ChangeLog:
    
            PR modula2/114929
            * gm2/pim/run/pass/testforloopzero.mod: New test.
            * gm2/pim/run/pass/testforloopzero2.mod: New test.
            * gm2/pim/run/pass/testforloopzero3.mod: New test.
            * gm2/pim/run/pass/testforloopzero4.mod: New test.
    
    (cherry picked from commit a561dc0f6c7085e102fe9e9b6abd7f2138512576)
    
    Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>

Diff:
---
 gcc/m2/gm2-compiler/M2Quads.mod                    | 191 +++++++++++++++++----
 gcc/testsuite/gm2/pim/run/pass/testforloopzero.mod |  33 ++++
 .../gm2/pim/run/pass/testforloopzero2.mod          |  35 ++++
 .../gm2/pim/run/pass/testforloopzero3.mod          |  32 ++++
 .../gm2/pim/run/pass/testforloopzero4.mod          |  32 ++++
 5 files changed, 289 insertions(+), 34 deletions(-)

diff --git a/gcc/m2/gm2-compiler/M2Quads.mod b/gcc/m2/gm2-compiler/M2Quads.mod
index 8a9a23013b2..3f414e186b2 100644
--- a/gcc/m2/gm2-compiler/M2Quads.mod
+++ b/gcc/m2/gm2-compiler/M2Quads.mod
@@ -4583,6 +4583,144 @@ BEGIN
 END BuildForLoopToRangeCheck ;
 
 
+(*
+   ForLoopLastIteratorVariable - assigns the last value of the index variable to
+                                 symbol LastIterator.
+                                 The For Loop is regarded:
+
+                                 For ident := e1 To e2 By BySym Do
+
+                                 End
+*)
+
+PROCEDURE ForLoopLastIteratorVariable (LastIterator, e1, e2, BySym, ByType: CARDINAL ;
+                                       e1tok, e2tok, bytok: CARDINAL) ;
+VAR
+   PBType,
+   PositiveBy,
+   ElseQuad,
+   t, f      : CARDINAL ;
+BEGIN
+   Assert (IsVar (LastIterator)) ;
+   (* If By > 0 then.  *)
+   (* q+1 if >=      by        0  q+3.  *)
+   (* q+2 GotoOp                  q+else.   *)
+   PushTFtok (BySym, ByType, bytok) ;  (* BuildRelOp  1st parameter *)
+   PushT (GreaterEqualTok) ;           (*             2nd parameter *)
+                                       (* 3rd parameter *)
+   PushZero (bytok, ByType) ;
+   BuildRelOp (e2tok) ;       (* Choose final expression position.  *)
+   PopBool (t, f) ;
+   BackPatch (t, NextQuad) ;
+
+   (* LastIterator := ((e2-e1) DIV By) * By + e1.  *)
+   PushTF (LastIterator, GetSType (LastIterator)) ;
+   PushTFtok (e2, GetSType (e2), e2tok) ;
+   PushT (MinusTok) ;
+   PushTFtok (e1, GetSType (e1), e1tok) ;
+   doBuildBinaryOp (TRUE, FALSE) ;
+   PushT (DivideTok) ;
+   PushTFtok (BySym, ByType, bytok) ;
+   doBuildBinaryOp (FALSE, FALSE) ;
+   PushT (TimesTok) ;
+   PushTFtok (BySym, ByType, bytok) ;
+   doBuildBinaryOp (FALSE, FALSE) ;
+   PushT (ArithPlusTok) ;
+   PushTFtok (e1, GetSType (e1), e1tok) ;
+   doBuildBinaryOp (FALSE, FALSE) ;
+   BuildForLoopToRangeCheck ;
+   BuildAssignmentWithoutBounds (e1tok, FALSE, FALSE) ;
+   GenQuad (GotoOp, NulSym, NulSym, 0) ;
+   ElseQuad := NextQuad-1 ;
+
+   (* Else.  *)
+
+   BackPatch (f, NextQuad) ;
+
+   PushTtok (MinusTok, bytok) ;
+   PushTFtok (BySym, ByType, bytok) ;
+   BuildUnaryOp ;
+   PopTF (PositiveBy, PBType) ;  (* PositiveBy := - BySym.  *)
+
+   (* LastIterator := e1 - ((e1-e2) DIV PositiveBy) * PositiveBy.  *)
+   PushTF (LastIterator, GetSType (LastIterator)) ;
+   PushTFtok (e1, GetSType (e1), e1tok) ;
+   PushT (MinusTok) ;
+   PushTFtok (e1, GetSType (e1), e1tok) ;
+   PushT (MinusTok) ;
+   PushTFtok (e2, GetSType (e2), e2tok) ;
+   doBuildBinaryOp (TRUE, FALSE) ;
+   PushT (DivideTok) ;
+   PushTFtok (PositiveBy, ByType, bytok) ;
+   doBuildBinaryOp (FALSE, FALSE) ;
+   PushT (TimesTok) ;
+   PushTFtok (PositiveBy, ByType, bytok) ;
+   doBuildBinaryOp (FALSE, FALSE) ;
+   doBuildBinaryOp (FALSE, FALSE) ;
+   BuildForLoopToRangeCheck ;
+   BuildAssignmentWithoutBounds (e1tok, FALSE, FALSE) ;
+   BackPatch (ElseQuad, NextQuad) ;
+
+   (* End.  *)
+END ForLoopLastIteratorVariable ;
+
+
+(*
+   ForLoopLastIteratorConstant - assigns the last value of the index variable to
+                                 symbol LastIterator.
+                                 The For Loop is regarded:
+
+                                 For ident := e1 To e2 By BySym Do
+
+                                 End
+*)
+
+PROCEDURE ForLoopLastIteratorConstant (LastIterator, e1, e2, BySym, ByType: CARDINAL;
+                                       e1tok, e2tok, bytok: CARDINAL) ;
+BEGIN
+   Assert (IsConst (LastIterator)) ;
+   (* LastIterator := VAL (GetType (LastIterator), ((e2-e1) DIV By) * By + e1)  *)
+   PushTF (LastIterator, GetSType (LastIterator)) ;
+   PushTFtok (e2, GetSType (e2), e2tok) ;
+   PushT (MinusTok) ;
+   PushTFtok (e1, GetSType (e1), e1tok) ;
+   doBuildBinaryOp (TRUE, FALSE) ;
+   PushT (DivideTok) ;
+   PushTFtok (BySym, ByType, bytok) ;
+   doBuildBinaryOp (FALSE, FALSE) ;
+   PushT (TimesTok) ;
+   PushTFtok (BySym, ByType, bytok) ;
+   doBuildBinaryOp (FALSE, FALSE) ;
+   PushT (ArithPlusTok) ;
+   PushTFtok (e1, GetSType (e1), e1tok) ;
+   doBuildBinaryOp (FALSE, FALSE) ;
+   BuildForLoopToRangeCheck ;
+   BuildAssignmentWithoutBounds (e1tok, FALSE, FALSE)
+END ForLoopLastIteratorConstant ;
+
+
+(*
+   ForLoopLastIterator - calculate the last iterator value but avoid setting
+                         LastIterator twice if it is a constant (in the quads).
+                         In the ForLoopLastIteratorVariable case only one
+                         path will be chosen but at the time of quadruple
+                         generation we do not know the value of BySym.
+*)
+
+PROCEDURE ForLoopLastIterator (LastIterator, e1, e2, BySym, ByType: CARDINAL ;
+                               e1tok, e2tok, bytok: CARDINAL) ;
+BEGIN
+   IF IsVar (LastIterator)
+   THEN
+      ForLoopLastIteratorVariable (LastIterator, e1, e2, BySym, ByType,
+                                   e1tok, e2tok, bytok)
+   ELSE
+      ForLoopLastIteratorConstant (LastIterator, e1, e2, BySym, ByType,
+                                   e1tok, e2tok, bytok)
+   END
+END ForLoopLastIterator ;
+
+
 (*
    BuildForToByDo - Builds the For To By Do part of the For statement
                     from the quad stack.
@@ -4659,7 +4797,7 @@ VAR
    e2tok,
    idtok,
    bytok     : CARDINAL ;
-   FinalValue,
+   LastIterator,
    exit1,
    IdSym,
    BySym,
@@ -4686,55 +4824,40 @@ BEGIN
    BuildAssignmentWithoutBounds (idtok, TRUE, TRUE) ;
 
    UseLineNote (l2) ;
-   FinalValue := MakeTemporary (e2tok,
-                                AreConstant (IsConst (e1) AND IsConst (e2) AND
-                                            IsConst (BySym))) ;
-   PutVar (FinalValue, GetSType (IdSym)) ;
+   LastIterator := MakeTemporary (e2tok,
+                                  AreConstant (IsConst (e1) AND IsConst (e2) AND
+                                               IsConst (BySym))) ;
+   PutVar (LastIterator, GetSType (IdSym)) ;
    etype := MixTypes (GetSType (e1), GetSType (e2), e2tok) ;
    e1 := doConvert (etype, e1) ;
    e2 := doConvert (etype, e2) ;
 
-   PushTF (FinalValue, GetSType(FinalValue)) ;
-   PushTFtok (e2, GetSType(e2), e2tok) ;  (* FinalValue := ((e1-e2) DIV By) * By + e1 *)
-   PushT (MinusTok) ;
-   PushTFtok (e1, GetSType(e1), e1tok) ;
-   doBuildBinaryOp (TRUE, FALSE) ;
-   PushT (DivideTok) ;
-   PushTFtok (BySym, ByType, bytok) ;
-   doBuildBinaryOp (FALSE, FALSE) ;
-   PushT (TimesTok) ;
-   PushTFtok (BySym, ByType, bytok) ;
-   doBuildBinaryOp (FALSE, FALSE) ;
-   PushT (ArithPlusTok) ;
-   PushTFtok (e1, GetSType (e1), e1tok) ;
-   doBuildBinaryOp (FALSE, FALSE) ;
-   BuildForLoopToRangeCheck ;
-   BuildAssignmentWithoutBounds (e1tok, FALSE, FALSE) ;
+   ForLoopLastIterator (LastIterator, e1, e2, BySym, ByType, e1tok, e2tok, bytok) ;
 
    (* q+1 if >=      by        0  q+..2 *)
    (* q+2 GotoOp                  q+3   *)
-   PushTFtok (BySym, ByType, bytok) ;  (* BuildRelOp  1st parameter *)
-   PushT (GreaterEqualTok) ;           (*             2nd parameter *)
-                                       (* 3rd parameter *)
+   PushTFtok (BySym, ByType, bytok) ;  (* BuildRelOp  1st parameter.  *)
+   PushT (GreaterEqualTok) ;           (*             2nd parameter.  *)
+                                       (* 3rd parameter.  *)
    PushZero (bytok, ByType) ;
 
-   BuildRelOp (e2tok) ;       (* choose final expression position.  *)
-   PopBool(t, f) ;
-   BackPatch(f, NextQuad) ;
+   BuildRelOp (e2tok) ;           (* Choose final expression position.  *)
+   PopBool (t, f) ;
+   BackPatch (f, NextQuad) ;
    (* q+3 If >=       e1  e2      q+5  *)
    (* q+4 GotoOp                  Exit *)
    PushTFtok (e1, GetSType (e1), e1tok) ;  (* BuildRelOp  1st parameter *)
    PushT (GreaterEqualTok) ;               (*             2nd parameter *)
    PushTFtok (e2, GetSType (e2), e2tok) ;  (*             3rd parameter *)
-   BuildRelOp (e2tok) ;           (* choose final expression position.  *)
+   BuildRelOp (e2tok) ;           (* Choose final expression position.  *)
    PopBool (t1, exit1) ;
    BackPatch (t1, NextQuad) ;
-   PushFor (Merge (PopFor(), exit1)) ;    (* merge exit1 *)
+   PushFor (Merge (PopFor (), exit1)) ;    (* Merge exit1.  *)
 
    GenQuad (GotoOp, NulSym, NulSym, 0) ;
    ForLoop := NextQuad-1 ;
 
-   (* ELSE *)
+   (* ELSE.  *)
 
    BackPatch (t, NextQuad) ;
    PushTFtok (e2, GetSType(e2), e2tok) ; (* BuildRelOp  1st parameter *)
@@ -4743,16 +4866,16 @@ BEGIN
    BuildRelOp (e2tok) ;
    PopBool (t1, exit1) ;
    BackPatch (t1, NextQuad) ;
-   PushFor (Merge (PopFor (), exit1)) ;       (* merge exit1 *)
+   PushFor (Merge (PopFor (), exit1)) ;       (* Merge exit1.  *)
 
-   BackPatch(ForLoop, NextQuad) ; (* fixes the start of the for loop *)
+   BackPatch(ForLoop, NextQuad) ; (* Fixes the start of the for loop.  *)
    ForLoop := NextQuad ;
 
-   (* and set up the stack *)
+   (* And set up the stack.  *)
 
    PushTFtok (IdSym, GetSym (IdSym), idtok) ;
    PushTFtok (BySym, ByType, bytok) ;
-   PushTFtok (FinalValue, GetSType (FinalValue), e2tok) ;
+   PushTFtok (LastIterator, GetSType (LastIterator), e2tok) ;
    PushT (ForLoop) ;
    PushT (RangeId)
 END BuildForToByDo ;
diff --git a/gcc/testsuite/gm2/pim/run/pass/testforloopzero.mod b/gcc/testsuite/gm2/pim/run/pass/testforloopzero.mod
new file mode 100644
index 00000000000..5f00c6c6c9e
--- /dev/null
+++ b/gcc/testsuite/gm2/pim/run/pass/testforloopzero.mod
@@ -0,0 +1,33 @@
+MODULE testforloopzero ;
+
+FROM libc IMPORT printf, exit ;
+
+
+(*
+   test -
+*)
+
+PROCEDURE test ;
+VAR
+   i, n,
+   count: CARDINAL ;
+BEGIN
+   n := 5 ;
+   count := 0 ;
+   FOR i := n TO 0 BY -1 DO
+      printf ("i = %d, count = %d\n", i, count);
+      INC (count)
+   END ;
+   IF count = 6
+   THEN
+      printf ("for loop counting down passed\n")
+   ELSE
+      printf ("for loop counting down failed\n") ;
+      exit (1)
+   END
+END test ;
+
+
+BEGIN
+   test
+END testforloopzero.
diff --git a/gcc/testsuite/gm2/pim/run/pass/testforloopzero2.mod b/gcc/testsuite/gm2/pim/run/pass/testforloopzero2.mod
new file mode 100644
index 00000000000..bf826221d4a
--- /dev/null
+++ b/gcc/testsuite/gm2/pim/run/pass/testforloopzero2.mod
@@ -0,0 +1,35 @@
+MODULE testforloopzero2 ;
+
+FROM libc IMPORT printf, exit ;
+
+
+(*
+   test -
+*)
+
+PROCEDURE test ;
+VAR
+   i, n,
+   zero,
+   count: CARDINAL ;
+BEGIN
+   n := 5 ;
+   count := 0 ;
+   zero := 0 ;
+   FOR i := n TO zero BY -1 DO
+      printf ("i = %d, count = %d\n", i, count);
+      INC (count)
+   END ;
+   IF count = 6
+   THEN
+      printf ("for loop counting down passed\n")
+   ELSE
+      printf ("for loop counting down failed\n") ;
+      exit (1)
+   END
+END test ;
+
+
+BEGIN
+   test
+END testforloopzero2.
diff --git a/gcc/testsuite/gm2/pim/run/pass/testforloopzero3.mod b/gcc/testsuite/gm2/pim/run/pass/testforloopzero3.mod
new file mode 100644
index 00000000000..16a899d1328
--- /dev/null
+++ b/gcc/testsuite/gm2/pim/run/pass/testforloopzero3.mod
@@ -0,0 +1,32 @@
+MODULE testforloopzero3 ;
+
+FROM libc IMPORT printf, exit ;
+
+
+(*
+   test -
+*)
+
+PROCEDURE test ;
+VAR
+   i,
+   count: CARDINAL ;
+BEGIN
+   count := 0 ;
+   FOR i := 5 TO 0 BY -1 DO
+      printf ("i = %d, count = %d\n", i, count);
+      INC (count)
+   END ;
+   IF count = 6
+   THEN
+      printf ("for loop counting down passed\n")
+   ELSE
+      printf ("for loop counting down failed\n") ;
+      exit (1)
+   END
+END test ;
+
+
+BEGIN
+   test
+END testforloopzero3.
diff --git a/gcc/testsuite/gm2/pim/run/pass/testforloopzero4.mod b/gcc/testsuite/gm2/pim/run/pass/testforloopzero4.mod
new file mode 100644
index 00000000000..b969d55bfea
--- /dev/null
+++ b/gcc/testsuite/gm2/pim/run/pass/testforloopzero4.mod
@@ -0,0 +1,32 @@
+MODULE testforloopzero4 ;
+
+FROM libc IMPORT printf, exit ;
+
+
+(*
+   test -
+*)
+
+PROCEDURE test ;
+VAR
+   i,
+   count: INTEGER ;
+BEGIN
+   count := 0 ;
+   FOR i := 5 TO -5 BY -1 DO
+      printf ("i = %d, count = %d\n", i, count);
+      INC (count)
+   END ;
+   IF count = 11
+   THEN
+      printf ("for loop counting down (%d) passed\n", count)
+   ELSE
+      printf ("for loop counting down (%d) failed\n", count) ;
+      exit (1)
+   END
+END test ;
+
+
+BEGIN
+   test
+END testforloopzero4.


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