[gcc r11-8712] ipa-sra: Fix thinko when overriding safe_to_import_accesses (PR 101066)

[gcc r11-8712] ipa-sra: Fix thinko when overriding safe_to_import_accesses (PR 101066)

[Martin Jambor]

https://gcc.gnu.org/g:6745246120d18db857344894967f2dc9c586fd0a

commit r11-8712-g6745246120d18db857344894967f2dc9c586fd0a
Author: Martin Jambor <mjambor@suse.cz>
Date:   Fri Jul 9 16:09:53 2021 +0200

    ipa-sra: Fix thinko when overriding safe_to_import_accesses (PR 101066)
    
    The "new" IPA-SRA has a more difficult job than the previous
    not-truly-IPA version when identifying situations in which a parameter
    passed by reference can be passed into a third function and only thee
    converted to one passed by value (and possibly "split" at the same
    time).
    
    In order to allow this, two conditions must be fulfilled.  First the
    call to the third function must happen before any modifications of
    memory, because it could change the value passed by reference.
    Second, in order to make sure we do not introduce new (invalid)
    dereferences, the call must postdominate the entry BB.
    
    The second condition is actually not necessary if the caller function
    is also certain to dereference the pointer but the first one must
    still hold.  Unfortunately, the code making this overriding decision
    also happen to trigger when the first condition is not fulfilled.
    This is fixed in the following patch.
    
    gcc/ChangeLog:
    
    2021-06-16  Martin Jambor  <mjambor@suse.cz>
    
            PR ipa/101066
            * ipa-sra.c (class isra_call_summary): New member
            m_before_any_store, initialize it in the constructor.
            (isra_call_summary::dump): Dump the new field.
            (ipa_sra_call_summaries::duplicate): Copy it.
            (process_scan_results): Set it.
            (isra_write_edge_summary): Stream it.
            (isra_read_edge_summary): Likewise.
            (param_splitting_across_edge): Only override
            safe_to_import_accesses if m_before_any_store is set.
    
    gcc/testsuite/ChangeLog:
    
    2021-06-16  Martin Jambor  <mjambor@suse.cz>
    
            PR ipa/101066
            * gcc.dg/ipa/pr101066.c: New test.
    
    (cherry picked from commit 763121ccd908f52bc666f277ea2cf42110b3aad9)

Diff:
---
 gcc/ipa-sra.c                       | 15 +++++++++++++--
 gcc/testsuite/gcc.dg/ipa/pr101066.c | 20 ++++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/gcc/ipa-sra.c b/gcc/ipa-sra.c
index 1571921cb48..7f77cb957ee 100644
--- a/gcc/ipa-sra.c
+++ b/gcc/ipa-sra.c
@@ -343,7 +343,7 @@ class isra_call_summary
 public:
   isra_call_summary ()
     : m_arg_flow (), m_return_ignored (false), m_return_returned (false),
-      m_bit_aligned_arg (false)
+      m_bit_aligned_arg (false), m_before_any_store (false)
   {}
 
   void init_inputs (unsigned arg_count);
@@ -362,6 +362,10 @@ public:
 
   /* Set when any of the call arguments are not byte-aligned.  */
   unsigned m_bit_aligned_arg : 1;
+
+  /* Set to true if the call happend before any (other) store to memory in the
+     caller.  */
+  unsigned m_before_any_store : 1;
 };
 
 /* Class to manage function summaries.  */
@@ -491,6 +495,8 @@ isra_call_summary::dump (FILE *f)
     fprintf (f, "    return value ignored\n");
   if (m_return_returned)
     fprintf (f, "    return value used only to compute caller return value\n");
+  if (m_before_any_store)
+    fprintf (f, "    happens before any store to memory\n");
   for (unsigned i = 0; i < m_arg_flow.length (); i++)
     {
       fprintf (f, "    Parameter %u:\n", i);
@@ -535,6 +541,7 @@ ipa_sra_call_summaries::duplicate (cgraph_edge *, cgraph_edge *,
   new_sum->m_return_ignored = old_sum->m_return_ignored;
   new_sum->m_return_returned = old_sum->m_return_returned;
   new_sum->m_bit_aligned_arg = old_sum->m_bit_aligned_arg;
+  new_sum->m_before_any_store = old_sum->m_before_any_store;
 }
 
 
@@ -2374,6 +2381,7 @@ process_scan_results (cgraph_node *node, struct function *fun,
 	unsigned count = gimple_call_num_args (call_stmt);
 	isra_call_summary *csum = call_sums->get_create (cs);
 	csum->init_inputs (count);
+	csum->m_before_any_store = uses_memory_as_obtained;
 	for (unsigned argidx = 0; argidx < count; argidx++)
 	  {
 	    if (!csum->m_arg_flow[argidx].pointer_pass_through)
@@ -2547,6 +2555,7 @@ isra_write_edge_summary (output_block *ob, cgraph_edge *e)
   bp_pack_value (&bp, csum->m_return_ignored, 1);
   bp_pack_value (&bp, csum->m_return_returned, 1);
   bp_pack_value (&bp, csum->m_bit_aligned_arg, 1);
+  bp_pack_value (&bp, csum->m_before_any_store, 1);
   streamer_write_bitpack (&bp);
 }
 
@@ -2665,6 +2674,7 @@ isra_read_edge_summary (struct lto_input_block *ib, cgraph_edge *cs)
   csum->m_return_ignored = bp_unpack_value (&bp, 1);
   csum->m_return_returned = bp_unpack_value (&bp, 1);
   csum->m_bit_aligned_arg = bp_unpack_value (&bp, 1);
+  csum->m_before_any_store = bp_unpack_value (&bp, 1);
 }
 
 /* Read intraprocedural analysis information about NODE and all of its outgoing
@@ -3421,7 +3431,8 @@ param_splitting_across_edge (cgraph_edge *cs)
 	    }
 	  else if (!ipf->safe_to_import_accesses)
 	    {
-	      if (!all_callee_accesses_present_p (param_desc, arg_desc))
+	      if (!csum->m_before_any_store
+		  || !all_callee_accesses_present_p (param_desc, arg_desc))
 		{
 		  if (dump_file && (dump_flags & TDF_DETAILS))
 		    fprintf (dump_file, "  %u->%u: cannot import accesses.\n",
diff --git a/gcc/testsuite/gcc.dg/ipa/pr101066.c b/gcc/testsuite/gcc.dg/ipa/pr101066.c
new file mode 100644
index 00000000000..1ceb6e43136
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/pr101066.c
@@ -0,0 +1,20 @@
+/* { dg-do run } */
+/* { dg-options "-Os -fno-ipa-cp -fno-inline" } */
+
+int a = 1, c, d, e;
+int *b = &a;
+static int g(int *h) {
+  c = *h;
+  return d;
+}
+static void f(int *h) {
+  e = *h;
+  *b = 0;
+  g(h);
+}
+int main() {
+  f(b);
+  if (c)
+    __builtin_abort();
+  return 0;
+}