PR c++/85746: Don't fold __builtin_constant_p prematurely

2019-10-22  Marc Glisse  <marc.glisse@inria.fr>

gcc/cp/
	* constexpr.c (cxx_eval_builtin_function_call): Only set
	force_folding_builtin_constant_p if manifestly_const_eval.

gcc/testsuite/
	* g++.dg/pr85746.C: New file.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@277292 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index d09f391be61c6d05c6fc05a8b14a9a5d7f6cd496..d2b1fe457cb9b80603556ca4ffda1fb6ac07476d 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2019-10-22  Marc Glisse  <marc.glisse@inria.fr>
+
+       PR c++/85746
+       * constexpr.c (cxx_eval_builtin_function_call): Only set
+       force_folding_builtin_constant_p if manifestly_const_eval.
+
 2019-10-22  Richard Sandiford  <richard.sandiford@arm.com>
 
        * cp-tree.h (STF_USER_VISIBLE): New constant.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 60d4b9ad0248807d84993db652eb9ea2ed36b3aa..2e1b9b765491772cd35ad409ecd09351afde42a2 100644 (file)
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1260,7 +1260,7 @@ cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun,
     }
 
   bool save_ffbcp = force_folding_builtin_constant_p;
-  force_folding_builtin_constant_p = true;
+  force_folding_builtin_constant_p |= ctx->manifestly_const_eval;
   tree save_cur_fn = current_function_decl;
   /* Return name of ctx->call->fundef->decl for __builtin_FUNCTION ().  */
   if (fndecl_built_in_p (fun, BUILT_IN_FUNCTION)

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 0581b5f50c910e854ec3f03780e110abbf90bcd4..fd272807d0ba4f65c8975c7e16c320deff7632b5 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2019-10-22  Marc Glisse  <marc.glisse@inria.fr>
+
+       PR c++/85746
+       * g++.dg/pr85746.C: New file.
+
 2019-10-22  Richard Biener  <rguenther@suse.de>
 
        PR tree-optimization/92173

diff --git a/gcc/testsuite/g++.dg/pr85746.C b/gcc/testsuite/g++.dg/pr85746.C
new file mode 100644 (file)
index 0000000..25f6795
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr85746.C
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-gimple" } */
+
+int f(int a,int b){
+  // The front-end should not fold this to 0.
+  int c = __builtin_constant_p(a < b);
+  return c;
+}
+
+/* { dg-final { scan-tree-dump "__builtin_constant_p" "gimple" } } */