[gcc r12-7026] debug/104337 - avoid messing with the abstract origin chain in NRV

[Richard Biener]

https://gcc.gnu.org/g:1d5c7584fd6e72bfdbede86cef5ff04ae35f9744

commit r12-7026-g1d5c7584fd6e72bfdbede86cef5ff04ae35f9744
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Feb 3 11:20:59 2022 +0100

    debug/104337 - avoid messing with the abstract origin chain in NRV
    
    The following avoids NRV from massaging DECL_ABSTRACT_ORIGIN after
    variable creation since NRV runs _after_ the function was inlined and thus
    affects the inlined variables copy indirectly.  We may adjust the abstract
    origin of a variable only at the point we create it, not further along the
    path since otherwise the (new) invariant that the abstract origin is always
    the ultimate origin cannot be maintained.
    
    The intent of what NRV does is OK I guess and it may improve the debug
    experience.  But I also notice we do
    
      SET_DECL_VALUE_EXPR (found, result);
      DECL_HAS_VALUE_EXPR_P (found) = 1;
    
    the code is there since the merge from tree-ssa which added tree-nrv.c.
    
    Jakub added the DECL_VALUE_EXPR in g:938650d8fddb878f623e315f0b7fd94b217efa96
    and Jason added the abstract origin setting conditional in g:7716876bbd3a
    
    The follwoing takes the radical approach and remove the attempt
    to "optimize" the debug info.
    
    The gdb testsuites show no regressions.
    
    2022-02-03  Richard Biener  <rguenther@suse.de>
    
            PR debug/104337
            * tree-nrv.cc (pass_nrv::execute): Remove tieing result and found
            together via DECL_ABSTRACT_ORIGIN.
    
            * gcc.dg/debug/pr104337.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/debug/pr104337.c | 15 +++++++++++++++
 gcc/tree-nrv.cc                       | 13 -------------
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/debug/pr104337.c b/gcc/testsuite/gcc.dg/debug/pr104337.c
new file mode 100644
index 00000000000..d15680fbf1a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/pr104337.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+
+struct a {
+  unsigned b : 7;
+};
+inline __attribute__((optimize(3))) __attribute__((always_inline)) struct a
+c() {
+  struct a d;
+  return d;
+}
+void e() {
+  for (;;)
+    c();
+}
+int main() {}
diff --git a/gcc/tree-nrv.cc b/gcc/tree-nrv.cc
index a67736dae5c..b96d5b86f27 100644
--- a/gcc/tree-nrv.cc
+++ b/gcc/tree-nrv.cc
@@ -236,19 +236,6 @@ pass_nrv::execute (function *fun)
       fprintf (dump_file, "\n");
     }
 
-  /* At this point we know that all the return statements return the
-     same local which has suitable attributes for NRV.   Copy debugging
-     information from FOUND to RESULT if it will be useful.  But don't set
-     DECL_ABSTRACT_ORIGIN to point at another function.  */
-  if (!DECL_IGNORED_P (found)
-      && !(DECL_ABSTRACT_ORIGIN (found)
-	   && DECL_CONTEXT (DECL_ABSTRACT_ORIGIN (found)) != current_function_decl))
-    {
-      DECL_NAME (result) = DECL_NAME (found);
-      DECL_SOURCE_LOCATION (result) = DECL_SOURCE_LOCATION (found);
-      DECL_ABSTRACT_ORIGIN (result) = DECL_ABSTRACT_ORIGIN (found);
-    }
-
   TREE_ADDRESSABLE (result) |= TREE_ADDRESSABLE (found);
 
   /* Now walk through the function changing all references to VAR to be