Docs, OpenMP: Correct internal documentation of OMP_FOR.

gcc/ChangeLog:

	* doc/generic.texi (OpenMP): Document OMP_SIMD, OMP_DISTRIBUTE,
	OMP_TASKLOOP, and OMP_LOOP with OMP_FOR.  Document how collapsed
	loops are represented and which fields are vectors.  Add
	documentation for OMP_FOR_PRE_BODY field.  Document internal
	form of non-rectangular loops and OMP_FOR_NON_RECTANGULAR.

	* tree.def (OMP_FOR): Make documentation consistent with the
	Texinfo manual, to fill some gaps and correct errors.

1 files changed, 54 insertions, 16 deletions

diff --git a/gcc/doc/generic.texi b/gcc/doc/generic.texi
index ad1270f..2c14b7a 100644
--- a/gcc/doc/generic.texi
+++ b/gcc/doc/generic.texi
@@ -2253,6 +2253,10 @@ edge.  Rethrowing the exception is represented using @code{RESX_EXPR}.
 @subsection OpenMP
 @tindex OMP_PARALLEL
 @tindex OMP_FOR
+@tindex OMP_SIMD
+@tindex OMP_DISTRIBUTE
+@tindex OMP_TASKLOOP
+@tindex OMP_LOOP
 @tindex OMP_SECTIONS
 @tindex OMP_SINGLE
 @tindex OMP_SECTION
@@ -2294,37 +2298,71 @@ the @code{VAR_DECL} that contains all the shared values and
 variables.
 
 @item OMP_FOR
+@itemx OMP_SIMD
+@itemx OMP_DISTRIBUTE
+@itemx OMP_TASKLOOP
+@itemx OMP_LOOP
 
-Represents @code{#pragma omp for [clause1 @dots{} clauseN]}.  It has
-six operands:
+Represents @code{#pragma omp for [clause1 @dots{} clauseN]} and
+related loop constructs (respectively).
+
+A single @code{OMP_FOR} node represents an entire nest of collapsed
+loops; as noted below, some of its arguments are vectors of length
+equal to the collapse depth, and the corresponding elements holding
+data specific to a particular loop in the nest.  These vectors are
+numbered from the outside in so that the outermost loop is element 0.
+
+These constructs have seven operands:
 
 Operand @code{OMP_FOR_BODY} contains the loop body.
 
 Operand @code{OMP_FOR_CLAUSES} is the list of clauses
 associated with the directive.
 
-Operand @code{OMP_FOR_INIT} is the loop initialization code of
-the form @code{VAR = N1}.
+Operand @code{OMP_FOR_INIT} is a vector containing iteration
+variable initializations of the form @code{VAR = N1}.
 
-Operand @code{OMP_FOR_COND} is the loop conditional expression
-of the form @code{VAR @{<,>,<=,>=@} N2}.
+Operand @code{OMP_FOR_COND} is vector containing loop
+conditional expressions of the form @code{VAR @{<,>,<=,>=@} N2}.
 
-Operand @code{OMP_FOR_INCR} is the loop index increment of the
-form @code{VAR @{+=,-=@} INCR}.
+Operand @code{OMP_FOR_INCR} is a vector containing loop index
+increment expressions of the form @code{VAR @{+=,-=@} INCR}.
 
 Operand @code{OMP_FOR_PRE_BODY} contains side effect code from
 operands @code{OMP_FOR_INIT}, @code{OMP_FOR_COND} and
-@code{OMP_FOR_INC}.  These side effects are part of the
+@code{OMP_FOR_INCR}.  These side effects are part of the
 @code{OMP_FOR} block but must be evaluated before the start of
-loop body.
+loop body.  @code{OMP_FOR_PRE_BODY} specifically
+includes @code{DECL_EXPR}s for iteration variables that are
+declared in the nested @code{for} loops.
+Note this field is not a vector; it may be null, but otherwise is
+usually a statement list collecting the side effect code from all
+the collapsed loops.
+
+Operand @code{OMP_FOR_ORIG_DECLS} holds @code{VAR_DECLS} for the
+original user-specified iterator variables in the source code.
+In some cases, like C++ class iterators or range @code{for} with
+decomposition, the @code{for} loop is rewritten by the front end to
+use a temporary iteration variable.  The purpose of this field is to
+make the original variables available to the gimplifier so it can
+adjust their data-sharing attributes and diagnose errors.
+@code{OMP_FOR_ORIG_DECLS} is a vector field, with each element holding
+a list of @code{VAR_DECLS} for the corresponding collapse level.
 
 The loop index variable @code{VAR} must be a signed integer variable,
-which is implicitly private to each thread.  Bounds
-@code{N1} and @code{N2} and the increment expression
-@code{INCR} are required to be loop invariant integer
-expressions that are evaluated without any synchronization. The
-evaluation order, frequency of evaluation and side effects are
-unspecified by the standard.
+which is implicitly private to each thread.  For rectangular loops,
+the bounds @code{N1} and @code{N2} and the increment expression
+@code{INCR} are required to be loop-invariant integer expressions
+that are evaluated without any synchronization.  The evaluation order,
+frequency of evaluation and side effects are otherwise unspecified
+by the standard.
+
+For non-rectangular loops, in which the bounds of an inner loop depend
+on the index of an outer loop, the bit @code{OMP_FOR_NON_RECTANGULAR}
+must be set.  In this case @code{N1} and @code{N2} are not ordinary
+expressions, but instead a @code{TREE_VEC} with three elements:
+the @code{DECL} for the outer loop variable, a multiplication
+factor, and an offset.
 
 @item OMP_SECTIONS