From: glisse <glisse@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Tue, 22 Oct 2019 14:42:38 +0000 (+0000)
Subject: PR c++/85746: Don't fold __builtin_constant_p prematurely
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=57f5992bc1ca544d597e99b7bf5eaa2b30c164d1;p=thirdparty%2Fgcc.git

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 d09f391be61c..d2b1fe457cb9 100644
--- 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 60d4b9ad0248..2e1b9b765491 100644
--- 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 0581b5f50c91..fd272807d0ba 100644
--- 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
index 000000000000..25f6795c6d61
--- /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" } } */