Re: [PATCH, OpenACC 2.7] Connect readonly modifier to points-to analysis

[Chung-Lin Tang <cltang@pllab.cs.nthu.edu.tw>]

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Hi Richard, Thomas,

On 2023/10/30 8:46 PM, Richard Biener wrote:
>>
>> What Chung-Lin's first patch does is mark the OMP clause for 'x' (not the
>> 'x' decl itself!) as 'readonly', via a new 'OMP_CLAUSE_MAP_READONLY'
>> flag.
>>
>> The actual optimization then is done in this second patch.  Chung-Lin
>> found that he could use 'SSA_NAME_POINTS_TO_READONLY_MEMORY' for that.
>> I don't have much experience with most of the following generic code, so
>> would appreciate a helping hand, whether that conceptually makes sense as
>> well as from the implementation point of view:

First of all, I have removed all of the gimplify-stage scanning and setting of
DECL_POINTS_TO_READONLY and SSA_NAME_POINTS_TO_READONLY_MEMORY (so no changes to
gimplify.cc now)

I remember this code was an artifact of earlier attempts to allow struct-member
pointer mappings to also work (e.g. map(readonly:rec.ptr[:N])), but failed anyways.
I think the omp_data_* member accesses when building child function side
receiver_refs is blocking points-to analysis from working (didn't try digging deeper)

Also during gimplify, VAR_DECLs appeared to be reused (at least in some cases) for map
clause decl reference building, so hoping that the variables "happen to be" single-use and
DECL_POINTS_TO_READONLY relaying into SSA_NAME_POINTS_TO_READONLY_MEMORY does appear to be
a little risky.

However, for firstprivate pointers processed during omp-low, it appears to be somewhat different.
(see below description)

> No, I don't think you can use that flag on non-default-defs, nor
> preserve it on copying.  So
> it also doesn't nicely extend to DECLs as done by the patch.  We
> currently _only_ use it
> for incoming parameters.  When used on arbitrary code you can get to for example
> 
> ptr1(points-to-readony-memory) = &p->x;
> ... access via ptr1 ...
> ptr2 = &p->x;
> ... access via ptr2 ...
> 
> where both are your OMP regions differently constrained (the constrain is on the
> code in the region, _not_ on the actual protections of the pointed to
> data, much like
> for the fortran case).  But now CSE comes along and happily replaces all ptr2
> with ptr2 in the second region and ... oops!

Richard, I assume what you meant was "happily replaces all ptr2 with ptr1 in the second region"?

That doesn't happen, because during omp-lower/expand, OMP target regions (which is all that
this applies currently) is separated into different individual child functions.

(Currently, the only "effective" use of DECL_POINTS_TO_READONLY is during omp-lower, when
for firstprivate pointers (i.e. 'a' here) we set this bit when constructing the first load
of this pointer)

  #pragma acc parallel copyin(readonly: a[:32]) copyout(r)
  {
    foo (a, a[8]);
    r = a[8];
  }
  #pragma acc parallel copyin(readonly: a[:32]) copyout(r)
  {
    foo (a, a[12]);
    r = a[12];
  }

After omp-expand (before SSA):

__attribute__((oacc parallel, omp target entrypoint, noclone))
void main._omp_fn.1 (const struct .omp_data_t.3 & restrict .omp_data_i)
{
 ...
  <bb 5> :
  D.2962 = .omp_data_i->D.2947;
  a.8 = D.2962;
  r.1 = (*a.8)[12];
  foo (a.8, r.1);
  r.1 = (*a.8)[12];
  D.2965 = .omp_data_i->r;
  *D.2965 = r.1;
  return;
}

__attribute__((oacc parallel, omp target entrypoint, noclone))
void main._omp_fn.0 (const struct .omp_data_t.2 & restrict .omp_data_i)
{
  ...
  <bb 3> :
  D.2968 = .omp_data_i->D.2939;
  a.4 = D.2968;
  r.0 = (*a.4)[8];
  foo (a.4, r.0);
  r.0 = (*a.4)[8];
  D.2971 = .omp_data_i->r;
  *D.2971 = r.0;
  return;
}

So actually, the creating of DECL_POINTS_TO_READONLY and its relaying to
SSA_NAME_POINTS_TO_READONLY_MEMORY here, is actually quite similar to a default-def
for an PARM_DECL, at least conceptually.

(If offloading was structured significantly differently, say if child functions
were separated much earlier before omp-lowering, than this readonly-modifier might
possibly be a direct application of 'r' in the "fn spec" attribute)

Other changes since first version of patch include:
1) update of C/C++ FE changes to new style in c-family/c-omp.cc
2) merging of two if cases in fortran/trans-openmp.cc like Thomas suggested
3) Update of readonly-2.c testcase to scan before/after "fre1" pass, to verify removal of a MEM load, also as Thomas suggested.

I have re-tested this patch using mainline, with no regressions. Is this okay for mainline?

Thanks,
Chung-Lin

2024-04-03  Chung-Lin Tang  <cltang@baylibre.com>

gcc/c-family/ChangeLog:

	* c-omp.cc (c_omp_address_inspector::expand_array_base):
	Set OMP_CLAUSE_MAP_POINTS_TO_READONLY on pointer clause.
	(c_omp_address_inspector::expand_component_selector): Likewise.

gcc/fortran/ChangeLog:

	* trans-openmp.cc (gfc_trans_omp_array_section):
	Set OMP_CLAUSE_MAP_POINTS_TO_READONLY on pointer clause.

gcc/ChangeLog:

	* gimple-expr.cc (copy_var_decl): Copy DECL_POINTS_TO_READONLY
	for VAR_DECLs.
	* omp-low.cc (lower_omp_target): Set DECL_POINTS_TO_READONLY for
	variables of receiver refs.
	* tree-pretty-print.cc (dump_omp_clause):
	Print OMP_CLAUSE_MAP_POINTS_TO_READONLY.
	(dump_generic_node): Print SSA_NAME_POINTS_TO_READONLY_MEMORY.
	* tree-ssanames.cc (make_ssa_name_fn): Set
	SSA_NAME_POINTS_TO_READONLY_MEMORY if DECL_POINTS_TO_READONLY is set.
	* tree.h (DECL_POINTS_TO_READONLY): New macro.
	(OMP_CLAUSE_MAP_POINTS_TO_READONLY): New macro.

gcc/testsuite/ChangeLog:

	* c-c++-common/goacc/readonly-1.c: Adjust testcase.
	* c-c++-common/goacc/readonly-2.c: New testcase.
	* gfortran.dg/goacc/readonly-1.f90: Adjust testcase.










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diff --git a/gcc/c-family/c-omp.cc b/gcc/c-family/c-omp.cc
index c0e02aa422f..458df1434ed 100644
--- a/gcc/c-family/c-omp.cc
+++ b/gcc/c-family/c-omp.cc
@@ -3907,6 +3907,8 @@ c_omp_address_inspector::expand_array_base (tree c,
     }
   else if (c2)
     {
+      if (OMP_CLAUSE_MAP_READONLY (c))
+	OMP_CLAUSE_MAP_POINTS_TO_READONLY (c2) = 1;
       OMP_CLAUSE_CHAIN (c2) = OMP_CLAUSE_CHAIN (c);
       OMP_CLAUSE_CHAIN (c) = c2;
       if (implicit_p)
@@ -4051,6 +4053,8 @@ c_omp_address_inspector::expand_component_selector (tree c,
     }
   else if (c2)
     {
+      if (OMP_CLAUSE_MAP_READONLY (c))
+	OMP_CLAUSE_MAP_POINTS_TO_READONLY (c2) = 1;
       OMP_CLAUSE_CHAIN (c2) = OMP_CLAUSE_CHAIN (c);
       OMP_CLAUSE_CHAIN (c) = c2;
       c = c2;
diff --git a/gcc/fortran/trans-openmp.cc b/gcc/fortran/trans-openmp.cc
index f867e2240bf..1b4bdb90cb6 100644
--- a/gcc/fortran/trans-openmp.cc
+++ b/gcc/fortran/trans-openmp.cc
@@ -2561,6 +2561,8 @@ gfc_trans_omp_array_section (stmtblock_t *block, gfc_exec_op op,
   ptr2 = fold_convert (ptrdiff_type_node, ptr2);
   OMP_CLAUSE_SIZE (node3) = fold_build2 (MINUS_EXPR, ptrdiff_type_node,
 					 ptr, ptr2);
+  if (n->u.map.readonly)
+    OMP_CLAUSE_MAP_POINTS_TO_READONLY (node3) = 1;
 }
 
 static tree
diff --git a/gcc/gimple-expr.cc b/gcc/gimple-expr.cc
index f8d7185530c..35aca9dc979 100644
--- a/gcc/gimple-expr.cc
+++ b/gcc/gimple-expr.cc
@@ -385,6 +385,8 @@ copy_var_decl (tree var, tree name, tree type)
   DECL_CONTEXT (copy) = DECL_CONTEXT (var);
   TREE_USED (copy) = 1;
   DECL_SEEN_IN_BIND_EXPR_P (copy) = 1;
+  if (VAR_P (var))
+    DECL_POINTS_TO_READONLY (copy) = DECL_POINTS_TO_READONLY (var);
   DECL_ATTRIBUTES (copy) = DECL_ATTRIBUTES (var);
   if (DECL_USER_ALIGN (var))
     {
diff --git a/gcc/omp-low.cc b/gcc/omp-low.cc
index 4d003f42098..3c1024d563a 100644
--- a/gcc/omp-low.cc
+++ b/gcc/omp-low.cc
@@ -14003,6 +14003,8 @@ lower_omp_target (gimple_stmt_iterator *gsi_p, omp_context *ctx)
 		if (ref_to_array)
 		  x = fold_convert_loc (clause_loc, TREE_TYPE (new_var), x);
 		gimplify_expr (&x, &new_body, NULL, is_gimple_val, fb_rvalue);
+		if (OMP_CLAUSE_MAP_POINTS_TO_READONLY (c) && VAR_P (x))
+		  DECL_POINTS_TO_READONLY (x) = 1;
 		if ((is_ref && !ref_to_array)
 		    || ref_to_ptr)
 		  {
diff --git a/gcc/testsuite/c-c++-common/goacc/readonly-1.c b/gcc/testsuite/c-c++-common/goacc/readonly-1.c
index 300464c92e3..88b6bb9efcf 100644
--- a/gcc/testsuite/c-c++-common/goacc/readonly-1.c
+++ b/gcc/testsuite/c-c++-common/goacc/readonly-1.c
@@ -48,17 +48,17 @@ int main (void)
 
 /* { dg-final { scan-tree-dump-times "(?n)#pragma acc declare map\\(to:y\\) map\\(readonly,to:s\\) map\\(readonly,to:x\\)" 1 "original" } } */
 
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc parallel map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c } } } } */
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc kernels map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c } } } } */
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc serial map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c } } } } */
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c } } } } */
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc enter data map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc parallel map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,firstprivate:x \\\[pointer assign, bias: 0\\\]\\)" 1 "original" { target { c } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc kernels map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,firstprivate:x \\\[pointer assign, bias: 0\\\]\\)" 1 "original" { target { c } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc serial map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,firstprivate:x \\\[pointer assign, bias: 0\\\]\\)" 1 "original" { target { c } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc enter data map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(readonly,to:\\*s.ptr \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c } } } } */
 
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc parallel map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c++ } } } } */
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc kernels map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c++ } } } } */
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc serial map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c++ } } } } */
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c++ } } } } */
-/* { dg-final { scan-tree-dump-times "(?n)#pragma acc enter data map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c++ } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc parallel map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,firstprivate:x \\\[pointer assign, bias: 0\\\]\\)" 1 "original" { target { c++ } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc kernels map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,firstprivate:x \\\[pointer assign, bias: 0\\\]\\)" 1 "original" { target { c++ } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc serial map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) .+ map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,firstprivate:x \\\[pointer assign, bias: 0\\\]\\)" 1 "original" { target { c++ } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c++ } } } } */
+/* { dg-final { scan-tree-dump-times "(?n)#pragma acc enter data map\\(to:y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\) map\\(readonly,to:\\*NON_LVALUE_EXPR <s.ptr> \\\[len: \[0-9\]+\\\]\\) map\\(pt_readonly,attach_detach:s.ptr \\\[bias: 0\\\]\\) map\\(readonly,to:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\)" 1 "original" { target { c++ } } } } */
 
 /* { dg-final { scan-tree-dump-times "(?n)#pragma acc cache \\(readonly:x\\\[0\\\] \\\[len: \[0-9\]+\\\]\\);$" 4 "original" } } */
 /* { dg-final { scan-tree-dump-times "(?n)#pragma acc cache \\(y\\\[0\\\] \\\[len: \[0-9\]+\\\]\\);$" 4 "original" } } */
diff --git a/gcc/testsuite/c-c++-common/goacc/readonly-2.c b/gcc/testsuite/c-c++-common/goacc/readonly-2.c
new file mode 100644
index 00000000000..3f52a9f6afb
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/goacc/readonly-2.c
@@ -0,0 +1,16 @@
+/* { dg-additional-options "-O -fdump-tree-phiprop -fdump-tree-fre" } */
+
+#pragma acc routine
+extern void foo (int *ptr, int val);
+
+int main (void)
+{
+  int r, a[32];
+  #pragma acc parallel copyin(readonly: a[:32]) copyout(r)
+  {
+    foo (a, a[8]);
+    r = a[8];
+  }
+}
+/* { dg-final { scan-tree-dump-times "r\.\[_0-9\]+ = MEM\\\[\[^_\]+_\[0-9\]+\\(ptro\\)\\\]\\\[8\\\];" 2 "phiprop1" } } */
+/* { dg-final { scan-tree-dump-times "r\.\[_0-9\]+ = MEM\\\[\[^_\]+_\[0-9\]+\\(ptro\\)\\\]\\\[8\\\];" 1 "fre1" } } */
diff --git a/gcc/testsuite/gfortran.dg/goacc/readonly-1.f90 b/gcc/testsuite/gfortran.dg/goacc/readonly-1.f90
index fc1e2719e67..cad449e6d40 100644
--- a/gcc/testsuite/gfortran.dg/goacc/readonly-1.f90
+++ b/gcc/testsuite/gfortran.dg/goacc/readonly-1.f90
@@ -80,16 +80,16 @@ end program main
 ! The front end turns OpenACC 'declare' into OpenACC 'data'.
 !   { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(readonly,to:\\*b\\) map\\(alloc:b.+ map\\(to:\\*c\\) map\\(alloc:c.+" 1 "original" } }
 !   { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(readonly,to:g\\) map\\(to:h\\)" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc parallel map\\(readonly,to:\\*.+ map\\(alloc:a.+ map\\(readonly,to:\\*.+ map\\(alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc parallel map\\(readonly,to:a.+ map\\(alloc:a.+ map\\(readonly,to:b.+ map\\(alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc kernels map\\(readonly,to:\\*.+ map\\(alloc:a.+ map\\(readonly,to:\\*.+ map\\(alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc kernels map\\(readonly,to:a.+ map\\(alloc:a.+ map\\(readonly,to:b.+ map\\(alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc serial map\\(readonly,to:\\*.+ map\\(alloc:a.+ map\\(readonly,to:\\*.+ map\\(alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc serial map\\(readonly,to:a.+ map\\(alloc:a.+ map\\(readonly,to:b.+ map\\(alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(readonly,to:\\*.+ map\\(alloc:a.+ map\\(readonly,to:\\*.+ map\\(alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(readonly,to:a.+ map\\(alloc:a.+ map\\(readonly,to:b.+ map\\(alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc enter data map\\(readonly,to:\\*.+ map\\(alloc:a.+ map\\(readonly,to:\\*.+ map\\(alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
-! { dg-final { scan-tree-dump-times "(?n)#pragma acc enter data map\\(readonly,to:a.+ map\\(alloc:a.+ map\\(readonly,to:b.+ map\\(alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc parallel map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc parallel map\\(readonly,to:a.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:b.+ map\\(pt_readonly,alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc kernels map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc kernels map\\(readonly,to:a.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:b.+ map\\(pt_readonly,alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc serial map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc serial map\\(readonly,to:a.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:b.+ map\\(pt_readonly,alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc data map\\(readonly,to:a.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:b.+ map\\(pt_readonly,alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc enter data map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:\\*.+ map\\(pt_readonly,alloc:b.+ map\\(to:\\*.+ map\\(alloc:c.+" 1 "original" } }
+! { dg-final { scan-tree-dump-times "(?n)#pragma acc enter data map\\(readonly,to:a.+ map\\(pt_readonly,alloc:a.+ map\\(readonly,to:b.+ map\\(pt_readonly,alloc:b.+ map\\(to:c.+ map\\(alloc:c.+" 1 "original" } }
 
 ! { dg-final { scan-tree-dump-times "(?n)#pragma acc cache \\(readonly:\\*\\(integer\\(kind=4\\)\\\[0:\\\] \\*\\) parm.*data \\\[len: .+\\\]\\) \\(readonly:\\*\\(integer\\(kind=4\\)\\\[0:\\\] \\*\\) parm.*data \\\[len: .+\\\]\\);" 8 "original" } }
 ! { dg-final { scan-tree-dump-times "(?n)#pragma acc cache \\(\\*\\(integer\\(kind=4\\)\\\[0:\\\] \\*\\) parm.*data \\\[len: .+\\\]\\);" 8 "original" } }
diff --git a/gcc/testsuite/gfortran.dg/pr67170.f90 b/gcc/testsuite/gfortran.dg/pr67170.f90
index 80236470f42..d7c33a4c3db 100644
--- a/gcc/testsuite/gfortran.dg/pr67170.f90
+++ b/gcc/testsuite/gfortran.dg/pr67170.f90
@@ -28,4 +28,4 @@ end subroutine foo
 end module test_module
 end program
 
-! { dg-final { scan-tree-dump-times "= \\*arg_\[0-9\]+\\(D\\);" 1 "fre1" } }
+! { dg-final { scan-tree-dump-times "= \\*arg_\[0-9\]+\\(D\\)\\(ptro\\);" 1 "fre1" } }
diff --git a/gcc/tree-pretty-print.cc b/gcc/tree-pretty-print.cc
index 926f7e006a7..62411a97ab9 100644
--- a/gcc/tree-pretty-print.cc
+++ b/gcc/tree-pretty-print.cc
@@ -915,6 +915,8 @@ dump_omp_clause (pretty_printer *pp, tree clause, int spc, dump_flags_t flags)
       pp_string (pp, "map(");
       if (OMP_CLAUSE_MAP_READONLY (clause))
 	pp_string (pp, "readonly,");
+      if (OMP_CLAUSE_MAP_POINTS_TO_READONLY (clause))
+	pp_string (pp, "pt_readonly,");
       switch (OMP_CLAUSE_MAP_KIND (clause))
 	{
 	case GOMP_MAP_ALLOC:
@@ -3620,6 +3622,8 @@ dump_generic_node (pretty_printer *pp, tree node, int spc, dump_flags_t flags,
 	pp_string (pp, "(D)");
       if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (node))
 	pp_string (pp, "(ab)");
+      if (SSA_NAME_POINTS_TO_READONLY_MEMORY (node))
+	pp_string (pp, "(ptro)");
       break;
 
     case WITH_SIZE_EXPR:
diff --git a/gcc/tree-ssanames.cc b/gcc/tree-ssanames.cc
index 1753a421a0b..cbdf4b11769 100644
--- a/gcc/tree-ssanames.cc
+++ b/gcc/tree-ssanames.cc
@@ -402,6 +402,9 @@ make_ssa_name_fn (struct function *fn, tree var, gimple *stmt,
   else
     SSA_NAME_RANGE_INFO (t) = NULL;
 
+  if (VAR_P (var) && DECL_POINTS_TO_READONLY (var))
+    SSA_NAME_POINTS_TO_READONLY_MEMORY (t) = 1;
+
   SSA_NAME_IN_FREE_LIST (t) = 0;
   SSA_NAME_IS_DEFAULT_DEF (t) = 0;
   init_ssa_name_imm_use (t);
diff --git a/gcc/tree.h b/gcc/tree.h
index b67a37d6522..1c5b883bc82 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -1036,6 +1036,13 @@ extern void omp_clause_range_check_failed (const_tree, const char *, int,
 #define DECL_HIDDEN_STRING_LENGTH(NODE) \
   (TREE_CHECK (NODE, PARM_DECL)->decl_common.decl_nonshareable_flag)
 
+/* In a VAR_DECL, set for variables regarded as pointing to memory not written
+   to. SSA_NAME_POINTS_TO_READONLY_MEMORY gets set for SSA_NAMEs created from
+   such VAR_DECLs. Currently used by OpenACC 'readonly' modifier in copyin
+   clauses.  */
+#define DECL_POINTS_TO_READONLY(NODE) \
+  (TREE_CHECK (NODE, VAR_DECL)->decl_common.decl_not_flexarray)
+
 /* In a CALL_EXPR, means that the call is the jump from a thunk to the
    thunked-to function.  Be careful to avoid using this macro when one of the
    next two applies instead.  */
@@ -1845,6 +1852,10 @@ class auto_suppress_location_wrappers
 #define OMP_CLAUSE_MAP_READONLY(NODE) \
   TREE_READONLY (OMP_CLAUSE_SUBCODE_CHECK (NODE, OMP_CLAUSE_MAP))
 
+/* Set if 'OMP_CLAUSE_DECL (NODE)' points to read-only memory.  */
+#define OMP_CLAUSE_MAP_POINTS_TO_READONLY(NODE) \
+  TREE_CONSTANT (OMP_CLAUSE_SUBCODE_CHECK (NODE, OMP_CLAUSE_MAP))
+
 /* Same as above, for use in OpenACC cache directives.  */
 #define OMP_CLAUSE__CACHE__READONLY(NODE) \
   TREE_READONLY (OMP_CLAUSE_SUBCODE_CHECK (NODE, OMP_CLAUSE__CACHE_))