[gcc/devel/ranger] c: Fix ICE with cast to VLA [93576]

[Aldy Hernandez]

https://gcc.gnu.org/g:bacdd5e978dad84e9c547b0d5c7fed14b8d75157

commit bacdd5e978dad84e9c547b0d5c7fed14b8d75157
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Feb 13 21:00:09 2020 +0100

    c: Fix ICE with cast to VLA [93576]
    
    The following testcase ICEs, because the PR84305 changes try to evaluate
    the size earlier.  If size has side-effects, that is desirable, and the
    side-effects will actually be wrapped in a SAVE_EXPR.  The problem on this
    testcase is that there are no side-effects, and c_fully_fold doesn't fold
    those COMPOUND_EXPRs to constant, and while before gimplification we unshare
    trees found in the expressions, the unsharing doesn't involve TYPE_SIZE etc.
    of used types.  Gimplification is destructive though, so when we gimplify
    the two nested COMPOUND_EXPRs and then try to gimplify it the second time
    for the TYPE_SIZEs, we ICE.
    Now, we could use unshare_expr in what we push to *expr, SAVE_EXPRs and
    their operands in there aren't unshared, but I really don't see a point of
    evaluating expressions that don't have side-effects before, so instead
    this just pushes there expressions that do have side-effects.
    
    2020-02-13  Jakub Jelinek  <jakub@redhat.com>
    
            PR c/93576
            * c-decl.c (grokdeclarator): If this_size_varies, only push size into
            *expr if it has side effects.
    
            * gcc.dg/pr93576.c: New test.

Diff:
---
 gcc/c/ChangeLog                |  6 ++++++
 gcc/c/c-decl.c                 | 13 ++++++++-----
 gcc/testsuite/ChangeLog        |  5 +++++
 gcc/testsuite/gcc.dg/pr93576.c | 10 ++++++++++
 4 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 995f315a803..e88337b18a0 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,9 @@
+2020-02-13  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/93576
+	* c-decl.c (grokdeclarator): If this_size_varies, only push size into
+	*expr if it has side effects.
+
 2020-01-30  Jeff Law  <law@redhat.com>
 
 	PR c/88660
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index 8281af7307a..1aa410db6e4 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -6512,11 +6512,14 @@ grokdeclarator (const struct c_declarator *declarator,
 		  }
 		if (this_size_varies)
 		  {
-		    if (*expr)
-		      *expr = build2 (COMPOUND_EXPR, TREE_TYPE (size),
-				      *expr, size);
-		    else
-		      *expr = size;
+		    if (TREE_SIDE_EFFECTS (size))
+		      {
+			if (*expr)
+			  *expr = build2 (COMPOUND_EXPR, TREE_TYPE (size),
+					  *expr, size);
+			else
+			  *expr = size;
+		      }
 		    *expr_const_operands &= size_maybe_const;
 		  }
 	      }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 560187c701a..a262bdde886 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-02-13  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/93576
+	* gcc.dg/pr93576.c: New test.
+
 2020-02-13  Sandra Loosemore  <sandra@codesourcery.com>
 
 	* g++.dg/cpp0x/constexpr-static13.C:
diff --git a/gcc/testsuite/gcc.dg/pr93576.c b/gcc/testsuite/gcc.dg/pr93576.c
new file mode 100644
index 00000000000..13c34f3771f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr93576.c
@@ -0,0 +1,10 @@
+/* PR c/93576 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+void
+foo (void)
+{
+  int b[] = { 0 };
+  (char (*)[(1, 7, 2)]) 0;
+}