PR17381: Treat undefined behavior during expression evaluation as an unmodeled

side-effect, so that we don't allow speculative evaluation of such expressions
during code generation.

This caused a diagnostic quality regression, so fix constant expression
diagnostics to prefer either the first "can't be constant folded" diagnostic or
the first "not a constant expression" diagnostic depending on the kind of
evaluation we're doing. This was always the intent, but didn't quite work
correctly before.

This results in certain initializers that used to be constant initializers to
no longer be; in particular, things like:

  float f = 1e100;

are no longer accepted in C. This seems appropriate, as such constructs would
lead to code being executed if sanitizers are enabled.

llvm-svn: 254574

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/test/Sema/integer-overflow.c b/clang/test/Sema/integer-overflow.c
index 44fbcd4c818..8f74873ed94 100644
--- a/clang/test/Sema/integer-overflow.c
+++ b/clang/test/Sema/integer-overflow.c
@@ -7,6 +7,7 @@ uint64_t f1(uint64_t, uint32_t);
 uint64_t f2(uint64_t, ...);
 
 static const uint64_t overflow = 1 * 4608 * 1024 * 1024; // expected-warning {{overflow in expression; result is 536870912 with type 'int'}}
+// expected-error@-1 {{not a compile-time constant}}
 
 uint64_t check_integer_overflows(int i) {
 // expected-warning@+1 {{overflow in expression; result is 536870912 with type 'int'}}