gimple-low: Fix up handling of volatile automatic vars in assume attribute [PR110754]

As the following testcases show, the gimple-low outlining of assume
magic functions handled volatile automatic vars (including
parameters/results) like non-volatile ones except it copied volatile
to the new PARM_DECL, which has the undesirable effect that a load
from the volatile var is passed to IFN_ASSUME and so there is a
side-effect there even when side-effects of the assume attribute
shouldn't be evaluated.

The following patch fixes that by passing address of the volatile
variables/parameters/results instead and doing loads or stores from it
or to it where it was originally accessed in the assume attribute
expression.

2024-02-10  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/110754
	* gimple-low.cc (assumption_copy_decl): For TREE_THIS_VOLATILE
	decls create PARM_DECL with pointer to original type, set
	TREE_READONLY and keep TREE_THIS_VOLATILE, TREE_ADDRESSABLE,
	DECL_NOT_GIMPLE_REG_P and DECL_BY_REFERENCE cleared.
	(adjust_assumption_stmt_op): For remapped TREE_THIS_VOLATILE decls
	wrap PARM_DECL into a simple TREE_THIS_NO_TRAP MEM_REF.
	(lower_assumption): For TREE_THIS_VOLATILE vars pass ADDR_EXPR
	of the var as argument.

	* gcc.dg/attr-assume-6.c: New test.
	* g++.dg/cpp23/attr-assume12.C: New test.

3 files changed, 50 insertions, 5 deletions

diff --git a/gcc/gimple-low.cc b/gcc/gimple-low.cc
index e19fc2c..e037198 100644
--- a/gcc/gimple-low.cc
+++ b/gcc/gimple-low.cc
@@ -374,15 +374,22 @@ assumption_copy_decl (tree decl, copy_body_data *id)
   gcc_assert (VAR_P (decl)
 	      || TREE_CODE (decl) == PARM_DECL
 	      || TREE_CODE (decl) == RESULT_DECL);
+  if (TREE_THIS_VOLATILE (decl))
+    type = build_pointer_type (type);
   tree copy = build_decl (DECL_SOURCE_LOCATION (decl),
 			  PARM_DECL, DECL_NAME (decl), type);
   if (DECL_PT_UID_SET_P (decl))
     SET_DECL_PT_UID (copy, DECL_PT_UID (decl));
-  TREE_ADDRESSABLE (copy) = TREE_ADDRESSABLE (decl);
-  TREE_READONLY (copy) = TREE_READONLY (decl);
-  TREE_THIS_VOLATILE (copy) = TREE_THIS_VOLATILE (decl);
-  DECL_NOT_GIMPLE_REG_P (copy) = DECL_NOT_GIMPLE_REG_P (decl);
-  DECL_BY_REFERENCE (copy) = DECL_BY_REFERENCE (decl);
+  TREE_THIS_VOLATILE (copy) = 0;
+  if (TREE_THIS_VOLATILE (decl))
+    TREE_READONLY (copy) = 1;
+  else
+    {
+      TREE_ADDRESSABLE (copy) = TREE_ADDRESSABLE (decl);
+      TREE_READONLY (copy) = TREE_READONLY (decl);
+      DECL_NOT_GIMPLE_REG_P (copy) = DECL_NOT_GIMPLE_REG_P (decl);
+      DECL_BY_REFERENCE (copy) = DECL_BY_REFERENCE (decl);
+    }
   DECL_ARG_TYPE (copy) = type;
   ((lower_assumption_data *) id)->decls.safe_push (decl);
   return copy_decl_for_dup_finish (id, decl, copy);
@@ -466,6 +473,11 @@ adjust_assumption_stmt_op (tree *tp, int *, void *datap)
     case PARM_DECL:
     case RESULT_DECL:
       *tp = remap_decl (t, &data->id);
+      if (TREE_THIS_VOLATILE (t) && *tp != t)
+	{
+	  *tp = build_simple_mem_ref (*tp);
+	  TREE_THIS_NOTRAP (*tp) = 1;
+	}
       break;
     default:
       break;
@@ -600,6 +612,11 @@ lower_assumption (gimple_stmt_iterator *gsi, struct lower_data *data)
       /* Remaining arguments will be the variables/parameters
 	 mentioned in the condition.  */
       vargs[i - sz] = lad.decls[i - 1];
+      if (TREE_THIS_VOLATILE (lad.decls[i - 1]))
+	{
+	  TREE_ADDRESSABLE (lad.decls[i - 1]) = 1;
+	  vargs[i - sz] = build_fold_addr_expr (lad.decls[i - 1]);
+	}
       /* If they have gimple types, we might need to regimplify
 	 them to make the IFN_ASSUME call valid.  */
       if (is_gimple_reg_type (TREE_TYPE (vargs[i - sz]))
diff --git a/gcc/testsuite/g++.dg/cpp23/attr-assume12.C b/gcc/testsuite/g++.dg/cpp23/attr-assume12.C
new file mode 100644
index 0000000..c955cd1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/attr-assume12.C
@@ -0,0 +1,14 @@
+// PR middle-end/110754
+// { dg-do compile { target c++11 } }
+// { dg-options "-O2 -fdump-tree-optimized" }
+// { dg-final { scan-tree-dump-times "a ={v} x" 1 "optimized" } }
+// { dg-final { scan-tree-dump-not "={v} a" "optimized" } }
+// { dg-final { scan-tree-dump-times "return 0;" 1 "optimized" } }
+
+int
+foo (int x)
+{
+  volatile int a = x;
+  [[gnu::assume (x == (a & 0))]];
+  return x;
+}
diff --git a/gcc/testsuite/gcc.dg/attr-assume-6.c b/gcc/testsuite/gcc.dg/attr-assume-6.c
new file mode 100644
index 0000000..346845f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/attr-assume-6.c
@@ -0,0 +1,14 @@
+/* PR middle-end/110754 */
+/* { dg-do compile } */
+/* { dg-options "-std=c23 -O2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump-times "a ={v} x" 1 "optimized" } } */
+/* { dg-final { scan-tree-dump-not "={v} a" "optimized" } } */
+/* { dg-final { scan-tree-dump-times "return 0;" 1 "optimized" } } */
+
+int
+foo (int x)
+{
+  volatile int a = x;
+  [[gnu::assume (x == (a & 0))]];
+  return x;
+}