On 3/9/21 10:31 AM, Jakub Jelinek wrote:
Hi!
My PR82304/PR95307 fix moved reinterpret cast from pointer to integer
diagnostics from cxx_eval_outermost_constant_expr where it caught
invalid code only at the outermost level down into
cxx_eval_constant_expression.
Unfortunately, it regressed following testcase, we emit worse code
including dynamic initialization of some vars.
While the initializers are not constant expressions due to the
reinterpret_cast in there, there is no reason not to fold them as an
optimization.
I've tried to make this dependent on !ctx->quiet, but that regressed
two further tests, so this patch bases that on manifestly_const_eval.
The new testcase is now optimized as much as it used to be in GCC 10
and the only regression it causes is an extra -Wnarrowing warning
on vla22.C test on invalid code (which the patch adjusts).
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
good for me, but I think Jason should also comment. Weaving both
consteval semantics and the need for sym+addend folding is tricky.
for avoidance of doubt, as mentioned in the PR, the inline variable case
is an ABI issue, not 'just nice'. I guess the ABI document should
specify. It doesn't appear to.
https://github.com/itanium-cxx-abi/cxx-abi/issues/121 created.
2021-03-09 Jakub Jelinek <ja...@redhat.com>
PR c++/99456
* constexpr.c (cxx_eval_constant_expression): For CONVERT_EXPR from
INDIRECT_TYPE_P to ARITHMETIC_TYPE_P, when !ctx->manifestly_const_eval
don't diagnose it, set *non_constant_p nor return t.
* g++.dg/opt/pr99456.C: New test.
* g++.dg/ext/vla22.C: Expect a -Wnarrowing warning for c++11 and
later.
--- gcc/cp/constexpr.c.jj 2021-03-08 23:40:28.334509562 +0100
+++ gcc/cp/constexpr.c 2021-03-09 11:50:08.721716460 +0100
@@ -6656,7 +6656,8 @@ cxx_eval_constant_expression (const cons
if (TREE_CODE (t) == CONVERT_EXPR
&& ARITHMETIC_TYPE_P (type)
- && INDIRECT_TYPE_P (TREE_TYPE (op)))
+ && INDIRECT_TYPE_P (TREE_TYPE (op))
+ && ctx->manifestly_const_eval)
{
if (!ctx->quiet)
error_at (loc,
--- gcc/testsuite/g++.dg/opt/pr99456.C.jj 2021-03-09 11:43:56.452862770
+0100
+++ gcc/testsuite/g++.dg/opt/pr99456.C 2021-03-09 11:43:56.452862770 +0100
@@ -0,0 +1,33 @@
+// PR c++/99456
+// { dg-do compile { target c++17 } }
+// { dg-options "-g0" }
+// { dg-final { scan-assembler-not "PR99456Var0\[1234]" } }
+// { dg-final { scan-assembler-not "__static_initialization_and_destruction" }
}
+// { dg-final { scan-assembler-not "_GLOBAL__sub_I" } }
+// { dg-final { scan-assembler-not "_ZGV12PR99456Var1\[1234]" } }
+
+typedef __UINTPTR_TYPE__ uintptr_t;
+
+class Container
+{
+public:
+ uintptr_t m;
+};
+
+extern unsigned desc;
+static constexpr unsigned &descRef = desc;
+
+inline Container PR99456Var01 {reinterpret_cast<uintptr_t> (&descRef)};
+inline Container PR99456Var02 {reinterpret_cast<uintptr_t> (&desc)};
+inline uintptr_t PR99456Var03 {reinterpret_cast<uintptr_t> (&descRef)};
+inline uintptr_t PR99456Var04 {reinterpret_cast<uintptr_t> (&desc)};
+
+inline Container PR99456Var11 {reinterpret_cast<uintptr_t> (&descRef)};
+inline Container PR99456Var12 {reinterpret_cast<uintptr_t> (&desc)};
+inline uintptr_t PR99456Var13 {reinterpret_cast<uintptr_t> (&descRef)};
+inline uintptr_t PR99456Var14 {reinterpret_cast<uintptr_t> (&desc)};
+
+auto *PR99456Ref11 = &PR99456Var11;
+auto *PR99456Ref12 = &PR99456Var12;
+auto *PR99456Ref13 = &PR99456Var13;
+auto *PR99456Ref14 = &PR99456Var14;
--- gcc/testsuite/g++.dg/ext/vla22.C.jj 2020-02-27 09:28:46.396956140 +0100
+++ gcc/testsuite/g++.dg/ext/vla22.C 2021-03-09 12:00:58.275482884 +0100
@@ -6,4 +6,4 @@ void
f ()
{
const int tbl[(long) "h"] = { 12 }; // { dg-error "size of array .tbl. is not an
integral constant-expression" }
-}
+} // { dg-warning "narrowing conversion" ""
{ target c++11 } .-1 }
Jakub
--
Nathan Sidwell
