-fcatch-undefined-behavior: add the -ftrapv checks to the set of things caught

by this mode, and also check for signed left shift overflow. The rules for the
latter are a little subtle:

 * neither C89 nor C++98 specify the behavior of a signed left shift at all
 * in C99 and C11, shifting a 1 bit into the sign bit has undefined behavior
 * in C++11, with core issue 1457, shifting a 1 bit *out* of the sign bit has
   undefined behavior

As of this change, we use the C99 rules for all C language variants, and the
C++11 rules for all C++ language variants. Once we have individual
-fcatch-undefined-behavior= flags, this should be revisited.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162634 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 20 insertions, 0 deletions

diff --git a/test/CodeGenCXX/catch-undef-behavior.cpp b/test/CodeGenCXX/catch-undef-behavior.cpp
index ed0a7763f5..0ec1cc1e05 100644
--- a/test/CodeGenCXX/catch-undef-behavior.cpp
+++ b/test/CodeGenCXX/catch-undef-behavior.cpp
@@ -66,3 +66,23 @@ void member_access(S *p) {
   // CHECK-NEXT: icmp eq i64 %[[MISALIGN]], 0
   k = p->f();
 }
+
+// CHECK: @_Z12lsh_overflow
+int lsh_overflow(int a, int b) {
+  // CHECK: %[[INBOUNDS:.*]] = icmp ule i32 %[[RHS:.*]], 31
+  // CHECK-NEXT: br i1 %[[INBOUNDS]]
+
+  // CHECK: %[[SHIFTED_OUT_WIDTH:.*]] = sub nuw nsw i32 31, %[[RHS]]
+  // CHECK-NEXT: %[[SHIFTED_OUT:.*]] = lshr i32 %[[LHS:.*]], %[[SHIFTED_OUT_WIDTH]]
+
+  // This is present for C++11 but not for C: C++ core issue 1457 allows a '1'
+  // to be shifted into the sign bit, but not out of it.
+  // CHECK-NEXT: %[[SHIFTED_OUT_NOT_SIGN:.*]] = lshr i32 %[[SHIFTED_OUT]], 1
+
+  // CHECK-NEXT: %[[NO_OVERFLOW:.*]] = icmp eq i32 %[[SHIFTED_OUT_NOT_SIGN]], 0
+  // CHECK-NEXT: br i1 %[[NO_OVERFLOW]]
+
+  // CHECK: %[[RET:.*]] = shl i32 %[[LHS]], %[[RHS]]
+  // CHECK-NEXT: ret i32 %[[RET]]
+  return a << b;
+}