From 49bb5a7e06049c771a28a2cc507c7789dc54a88b Mon Sep 17 00:00:00 2001
From: Michael Matz <matz@suse.de>
Date: Sat, 3 Sep 2016 23:23:13 +0200
Subject: [PATCH] Fix __builtin_constant_p(1000/x)

was incorrectly treated as constant because the vpop removed
all traces of non-constness.
---
 tccgen.c        | 17 +++++++++++++++++
 tests/tcctest.c | 10 ++++++++++
 2 files changed, 27 insertions(+)

diff --git a/tccgen.c b/tccgen.c
index cd6e690..f79d30e 100644
--- a/tccgen.c
+++ b/tccgen.c
@@ -1787,6 +1787,13 @@ static void gen_opic(int op)
                     gen_opi(op);
             } else {
                 vtop--;
+		/* Ensure vtop isn't marked VT_CONST in case something
+		   up our callchain is interested in const-ness of the
+		   expression.  Also make it a non-LVAL if it was,
+		   so that further code can't accidentally generate
+		   a deref (happen only for buggy uses of e.g.
+		   gv() under nocode_wanted).  */
+		vtop->r &= ~(VT_VALMASK | VT_LVAL);
             }
         }
     }
@@ -5014,6 +5021,16 @@ static void expr_cond(void)
             }
         }
         else {
+	    /* XXX This doesn't handle nocode_wanted correctly at all.
+	       It unconditionally calls gv/gvtst and friends.  That's
+	       the case for many of the expr_ routines.  Currently
+	       that should generate only useless code, but depending
+	       on other operand handling this might also generate
+	       pointer derefs for lvalue conversions whose result
+	       is useless, but nevertheless can lead to segfault.
+
+	       Somewhen we need to overhaul the whole nocode_wanted
+	       handling.  */
             if (vtop != vstack) {
                 /* needed to avoid having different registers saved in
                    each branch */
diff --git a/tests/tcctest.c b/tests/tcctest.c
index b8e534f..daf788c 100644
--- a/tests/tcctest.c
+++ b/tests/tcctest.c
@@ -1082,6 +1082,14 @@ static int toupper1(int a)
     return TOUPPER(a);
 }
 
+static unsigned int calc_vm_flags(unsigned int prot)
+{
+  unsigned int prot_bits;
+  /* This used to segfault in some revisions: */
+  prot_bits = ((0x1==0x00000001)?(prot&0x1):(prot&0x1)?0x00000001:0);
+  return prot_bits;
+}
+
 void bool_test()
 {
     int *s, a, b, t, f, i;
@@ -1154,6 +1162,7 @@ void bool_test()
         if (toupper1 (i) != TOUPPER (i))
             printf("error %d\n", i);
     }
+    printf ("bits = 0x%x\n", calc_vm_flags (0x1));
 }
 
 /* GCC accepts that */
@@ -2880,6 +2889,7 @@ void builtin_test(void)
     printf("res = %d\n", __builtin_constant_p(1 + 2));
     printf("res = %d\n", __builtin_constant_p(&constant_p_var));
     printf("res = %d\n", __builtin_constant_p(constant_p_var));
+    printf("res = %d\n", __builtin_constant_p(100000 / constant_p_var));
     s = 1;
     ll = 2;
     i = __builtin_choose_expr (1 != 0, ll, s);