Dead-field warning in structs at LTO-time

This commit includes the following components:

  Type-based escape analysis to determine structs that can be modified at
  link-time.
  Field access analysis to determine which fields are never read.

The type-based escape analysis provides a list of types, that are not
visible outside of the current linking unit (e.g. parameter types of external
functions).

The field access analyses non-escaping structs for fields that
are not used in the linking unit and thus can be removed.

1 files changed, 21 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/ipa/ipa-structreorg-04-layout-compile-0.c b/gcc/testsuite/gcc.dg/ipa/ipa-structreorg-04-layout-compile-0.c
new file mode 100644
index 00000000000..0424f4cb6ea
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/ipa-structreorg-04-layout-compile-0.c
@@ -0,0 +1,21 @@
+/* { dg-do run } */
+/* { dg-options  "-flto -fipa-type-escape-analysis -fdump-ipa-type-escape-analysis" } */
+
+#include <stddef.h>
+#include <assert.h>
+
+int
+main (int argc, char **argv)
+{
+  struct astruct_s
+  {
+    int a;
+    int b;
+    int c;
+  };
+  struct astruct_s astruct;
+  int *c = &astruct.c;
+  int *a = &astruct.a;
+  ptrdiff_t d = c - a;
+  assert (d == 1);
+}