[gcc(refs/vendors/ibm/heads/perf)] sra: Avoid totally scalarizing overallping field_decls (PR 93667)

[gcc(refs/vendors/ibm/heads/perf)] sra: Avoid totally scalarizing overallping field_decls (PR 93667)

[Jiu Fu Guo]

https://gcc.gnu.org/g:665c5bad168ab63629b29ed2ce08ed042c088dc2

commit 665c5bad168ab63629b29ed2ce08ed042c088dc2
Author: Martin Jambor <mjambor@suse.cz>
Date:   Wed Feb 19 11:08:40 2020 +0100

    sra: Avoid totally scalarizing overallping field_decls (PR 93667)
    
    [[no_unique_address]] C++ attribute can cause two fields of a
    RECORD_TYPE overlap, which currently confuses the totally scalarizing
    code into creating invalid access tree.  For GCC 10, I'd like to
    simply disable total scalarization of types where this happens.
    
    For GCC 11 I'll write down a TODO item to enable total scalarization
    of cases like this where the problematic fields are basically empty -
    despite having a non-zero size - i.e. when they are just RECORD_TYPEs
    without any data fields.
    
    2020-02-19  Martin Jambor  <mjambor@suse.cz>
    
            gcc/
    
            PR tree-optimization/93667
            * tree-sra.c (scalarizable_type_p): Return false if record fields
            do not follow wach other.
    
            gcc/testsuite/
    
            PR tree-optimization/93667
            * g++.dg/tree-ssa/pr93667.C: New test.

Diff:
---
 gcc/ChangeLog                           |  6 ++++++
 gcc/testsuite/ChangeLog                 |  5 +++++
 gcc/testsuite/g++.dg/tree-ssa/pr93667.C | 11 +++++++++++
 gcc/tree-sra.c                          | 14 ++++++++++++++
 4 files changed, 36 insertions(+)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 77c2a9ad810..6b53f9a2f07 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2020-02-19  Martin Jambor  <mjambor@suse.cz>
+
+	PR tree-optimization/93667
+	* tree-sra.c (scalarizable_type_p): Return false if record fields
+	do not follow wach other.
+
 2020-01-21  Kito Cheng  <kito.cheng@sifive.com>
 
 	* config/riscv/riscv.c (riscv_output_move) Using fmv.x.w/fmv.w.x
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9b4fe11a6f6..8033fa0a3bb 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-02-19  Martin Jambor  <mjambor@suse.cz>
+
+	PR tree-optimization/93667
+	* g++.dg/tree-ssa/pr93667.C: New test.
+
 2020-02-19  Hongtao Liu  <hongtao.liu@intel.com>
 
 	* g++.dg/other/i386-2.C: add -mavx512vbmi2
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr93667.C b/gcc/testsuite/g++.dg/tree-ssa/pr93667.C
new file mode 100644
index 00000000000..d875f53d9ec
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr93667.C
@@ -0,0 +1,11 @@
+// { dg-do compile }
+// { dg-options "-O2 -std=c++2a" } */
+
+struct a {};
+struct b { [[no_unique_address]] a aq; };
+struct c {
+  int d;
+  [[no_unique_address]] b e;
+};
+c f() {return {};}
+void g() { f(); }
diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index 0cfac0a8192..4c7d651e6b9 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -958,6 +958,9 @@ scalarizable_type_p (tree type, bool const_decl)
   if (type_contains_placeholder_p (type))
     return false;
 
+  bool have_predecessor_field = false;
+  HOST_WIDE_INT prev_pos = 0;
+
   switch (TREE_CODE (type))
   {
   case RECORD_TYPE:
@@ -966,6 +969,17 @@ scalarizable_type_p (tree type, bool const_decl)
 	{
 	  tree ft = TREE_TYPE (fld);
 
+	  if (zerop (DECL_SIZE (fld)))
+	    continue;
+
+	  HOST_WIDE_INT pos = int_bit_position (fld);
+	  if (have_predecessor_field
+	      && pos <= prev_pos)
+	    return false;
+
+	  have_predecessor_field = true;
+	  prev_pos = pos;
+
 	  if (DECL_BIT_FIELD (fld))
 	    return false;