[ubsan] Skip overflow checks on safe arithmetic (fixes PR32874)

Currently, ubsan emits overflow checks for arithmetic that is known to
be safe at compile-time, e.g:

  1 + 1 => CheckedAdd(1, 1)

This leads to breakage when using the __builtin_prefetch intrinsic. LLVM
expects the arguments to @llvm.prefetch to be constant integers, and
when ubsan inserts unnecessary checks on the operands to the intrinsic,
this contract is broken, leading to verifier failures (see PR32874).

Instead of special-casing __builtin_prefetch for ubsan, this patch fixes
the underlying problem, i.e that clang currently emits unnecessary
overflow checks.

Testing: I ran the check-clang and check-ubsan targets with a stage2,
ubsan-enabled build of clang. I added a regression test for PR32874, and
some extra checking to make sure we don't regress runtime checking for
unsafe arithmetic. The existing ubsan-promoted-arithmetic.cpp test also
provides coverage for this change.

llvm-svn: 301988

1 files changed, 61 insertions, 0 deletions

diff --git a/clang/test/CodeGen/PR32874.c b/clang/test/CodeGen/PR32874.c
new file mode 100644
index 00000000000..f8aa1c2a66f
--- /dev/null
+++ b/clang/test/CodeGen/PR32874.c
@@ -0,0 +1,61 @@
+// RUN: %clang_cc1 -x c -S -emit-llvm -o - -triple x86_64-apple-darwin10 %s \
+// RUN:   -w -fsanitize=signed-integer-overflow,unsigned-integer-overflow,integer-divide-by-zero,float-divide-by-zero \
+// RUN:   | FileCheck %s
+
+// CHECK-LABEL: define void @foo
+// CHECK-NOT: !nosanitize
+void foo(const int *p) {
+  // __builtin_prefetch expects its optional arguments to be constant integers.
+  // Check that ubsan does not instrument any safe arithmetic performed in
+  // operands to __builtin_prefetch. (A clang frontend check should reject
+  // unsafe arithmetic in these operands.)
+
+  __builtin_prefetch(p, 0 + 1, 0 + 3);
+  __builtin_prefetch(p, 1 - 0, 3 - 0);
+  __builtin_prefetch(p, 1 * 1, 1 * 3);
+  __builtin_prefetch(p, 1 / 1, 3 / 1);
+  __builtin_prefetch(p, 3 % 2, 3 % 1);
+
+  __builtin_prefetch(p, 0U + 1U, 0U + 3U);
+  __builtin_prefetch(p, 1U - 0U, 3U - 0U);
+  __builtin_prefetch(p, 1U * 1U, 1U * 3U);
+  __builtin_prefetch(p, 1U / 1U, 3U / 1U);
+  __builtin_prefetch(p, 3U % 2U, 3U % 1U);
+}
+
+// CHECK-LABEL: define void @ub_constant_arithmetic
+void ub_constant_arithmetic() {
+  // Check that we still instrument unsafe arithmetic, even if it is known to
+  // be unsafe at compile time.
+
+  int INT_MIN = 0xffffffff;
+  int INT_MAX = 0x7fffffff;
+
+  // CHECK: call void @__ubsan_handle_add_overflow
+  // CHECK: call void @__ubsan_handle_add_overflow
+  INT_MAX + 1;
+  INT_MAX + -1;
+
+  // CHECK: call void @__ubsan_handle_negate_overflow
+  // CHECK: call void @__ubsan_handle_sub_overflow
+  -INT_MIN;
+  -INT_MAX - 2;
+
+  // CHECK: call void @__ubsan_handle_mul_overflow
+  // CHECK: call void @__ubsan_handle_mul_overflow
+  INT_MAX * INT_MAX;
+  INT_MIN * INT_MIN;
+
+  // CHECK: call void @__ubsan_handle_divrem_overflow
+  // CHECK: call void @__ubsan_handle_divrem_overflow
+  1 / 0;
+  INT_MIN / -1;
+
+  // CHECK: call void @__ubsan_handle_divrem_overflow
+  // CHECK: call void @__ubsan_handle_divrem_overflow
+  1 % 0;
+  INT_MIN % -1;
+
+  // CHECK: call void @__ubsan_handle_divrem_overflow
+  1.0 / 0.0;
+}