[PATCH] c++: Error recovery with errenous DECL_INITIAL [PR94475]

[Patrick Palka via Gcc-patches]

Here we're ICE'ing in do_narrow during error-recovery, because ocp_convert
returns error_mark_node after it attempts to reduce a const decl to its
erroneous DECL_INITIAL via scalar_constant_value, and we later pass this
error_mark_node to fold_build2 which isn't prepared to handle error_mark_nodes.

We could fix this ICE in do_narrow by checking if ocp_convert returns
error_mark_node, but for the sake of consistency and for better error recovery
it seems it'd be better if ocp_convert didn't care that a const decl's
initializer is erroneous and would instead proceed as if the decl was not const,
which is the approach that this patch takes.

Passes 'make check-c++', does this look OK to commit after full bootstrap and
regtest?

gcc/cp/ChangeLog:

        PR c++/94475
        * cvt.c (ocp_convert): If the result of scalar_constant_value is
        erroneous, discard it and carry on with the original expression.

gcc/testsuite/ChangeLog:

        PR c++/94475
        * g++.dg/conversion/err-recover2.C: New test.
        * g++.dg/diagnostic/pr84138.C: Remove now-bogus warning.
        * g++.dg/warn/Wsign-compare-8.C: Remove now-bogus warning.
---
 gcc/cp/cvt.c                                   |  6 +++---
 gcc/testsuite/g++.dg/conversion/err-recover2.C | 10 ++++++++++
 gcc/testsuite/g++.dg/diagnostic/pr84138.C      |  2 +-
 gcc/testsuite/g++.dg/warn/Wsign-compare-8.C    |  2 +-
 4 files changed, 15 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/conversion/err-recover2.C

diff --git a/gcc/cp/cvt.c b/gcc/cp/cvt.c
index a3b80968b33..b94231a6d08 100644
--- a/gcc/cp/cvt.c
+++ b/gcc/cp/cvt.c
@@ -723,10 +723,10 @@ ocp_convert (tree type, tree expr, int convtype, int 
flags,
   if (!CLASS_TYPE_P (type))
     {
       e = mark_rvalue_use (e);
-      e = scalar_constant_value (e);
+      tree v = scalar_constant_value (e);
+      if (!error_operand_p (v))
+       e = v;
     }
-  if (error_operand_p (e))
-    return error_mark_node;
 
   if (NULLPTR_TYPE_P (type) && null_ptr_cst_p (e))
     {
diff --git a/gcc/testsuite/g++.dg/conversion/err-recover2.C 
b/gcc/testsuite/g++.dg/conversion/err-recover2.C
new file mode 100644
index 00000000000..437e1a919ea
--- /dev/null
+++ b/gcc/testsuite/g++.dg/conversion/err-recover2.C
@@ -0,0 +1,10 @@
+// PR c++/94475
+// { dg-do compile }
+
+unsigned char
+sr ()
+{
+  const unsigned char xz = EI; // { dg-error "not declared" }
+
+  return xz - (xz >> 1);
+}
diff --git a/gcc/testsuite/g++.dg/diagnostic/pr84138.C 
b/gcc/testsuite/g++.dg/diagnostic/pr84138.C
index 5c48b9b164a..00352306a56 100644
--- a/gcc/testsuite/g++.dg/diagnostic/pr84138.C
+++ b/gcc/testsuite/g++.dg/diagnostic/pr84138.C
@@ -5,4 +5,4 @@ foo()
 {
   const int i = 0 = 0; // { dg-error "lvalue required as left operand" }
   return 1 ? 0 : (char)i;
-} // { dg-warning "control reaches" }
+}
diff --git a/gcc/testsuite/g++.dg/warn/Wsign-compare-8.C 
b/gcc/testsuite/g++.dg/warn/Wsign-compare-8.C
index 237ba84d526..4d2688157fc 100644
--- a/gcc/testsuite/g++.dg/warn/Wsign-compare-8.C
+++ b/gcc/testsuite/g++.dg/warn/Wsign-compare-8.C
@@ -5,4 +5,4 @@ bool foo (char c)
 {
   const int i = 0 = 0; // { dg-error "lvalue" }
   return c = i;
-} // { dg-warning "control reaches" }
+}
-- 
2.26.1.107.gefe3874640