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llvm-project/compiler-rt/test/ubsan/TestCases/ImplicitConversion/integer-conversion-incdec.c

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[clang][CodeGen] Implicit Conversion Sanitizer: handle increment/decrement (PR44054)(take 2) Summary: Implicit Conversion Sanitizer is *almost* feature complete. There aren't *that* much unsanitized things left, two major ones are increment/decrement (this patch) and bit fields. As it was discussed in [[ https://bugs.llvm.org/show_bug.cgi?id=39519 | PR39519 ]], unlike `CompoundAssignOperator` (which is promoted internally), or `BinaryOperator` (for which we always have promotion/demotion in AST) or parts of `UnaryOperator` (we have promotion/demotion but only for certain operations), for inc/dec, clang omits promotion/demotion altogether, under as-if rule. This is technically correct: https://rise4fun.com/Alive/zPgD As it can be seen in `InstCombineCasts.cpp` `canEvaluateTruncated()`, `add`/`sub`/`mul`/`and`/`or`/`xor` operators can all arbitrarily be extended or truncated: https://github.com/llvm/llvm-project/blob/901cd3b3f62d0c700e5d2c3f97eff97d634bec5e/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp#L1320-L1334 But that has serious implications: 1. Since we no longer model implicit casts, do we pessimise their AST representation and everything that uses it? 2. There is no demotion, so lossy demotion sanitizer does not trigger :] Now, i'm not going to argue about the first problem here, but the second one **needs** to be addressed. As it was stated in the report, this is done intentionally, so changing this in all modes would be considered a penalization/regression. Which means, the sanitization-less codegen must not be altered. It was also suggested to not change the sanitized codegen to the one with demotion, but i quite strongly believe that will not be the wise choice here: 1. One will need to re-engineer the check that the inc/dec was lossy in terms of `@llvm.{u,s}{add,sub}.with.overflow` builtins 2. We will still need to compute the result we would lossily demote. (i.e. the result of wide `add`ition/`sub`traction) 3. I suspect it would need to be done right here, in sanitization. Which kinda defeats the point of using `@llvm.{u,s}{add,sub}.with.overflow` builtins: we'd have two `add`s with basically the same arguments, one of which is used for check+error-less codepath and other one for the error reporting. That seems worse than a single wide op+check. 4. OR, we would need to do that in the compiler-rt handler. Which means we'll need a whole new handler. But then what about the `CompoundAssignOperator`, it would also be applicable for it. So this also doesn't really seem like the right path to me. 5. At least X86 (but likely others) pessimizes all sub-`i32` operations (due to partial register stalls), so even if we avoid promotion+demotion, the computations will //likely// be performed in `i32` anyways. So i'm not really seeing much benefit of not doing the straight-forward thing. While looking into this, i have noticed a few more LLVM middle-end missed canonicalizations, and filed [[ https://bugs.llvm.org/show_bug.cgi?id=44100 | PR44100 ]], [[ https://bugs.llvm.org/show_bug.cgi?id=44102 | PR44102 ]]. Those are not specific to inc/dec, we also have them for `CompoundAssignOperator`, and it can happen for normal arithmetics, too. But if we take some other path in the patch, it will not be applicable here, and we will have most likely played ourselves. TLDR: front-end should emit canonical, easy-to-optimize yet un-optimized code. It is middle-end's job to make it optimal. I'm really hoping reviewers agree with my personal assessment of the path this patch should take.. This originally landed in 9872ea4ed1de4c49300430e4f1f4dfc110a79ab9 but got immediately reverted in cbfa237892e55b7129a1178c9b03f26683d643af because the assertion was faulty. That fault ended up being caused by the enum - while there will be promotion, both types are unsigned, with same width. So we still don't need to sanitize non-signed cases. So far. Maybe the assert will tell us this isn't so. Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=44054 | PR44054 ]]. Refs. https://github.com/google/sanitizers/issues/940 Reviewers: rjmccall, erichkeane, rsmith, vsk Reviewed By: erichkeane Subscribers: mehdi_amini, dexonsmith, cfe-commits, #sanitizers, llvm-commits, aaron.ballman, t.p.northover, efriedma, regehr Tags: #llvm, #clang, #sanitizers Differential Revision: https://reviews.llvm.org/D70539
2019-11-27 22:07:06 +08:00
// RUN: %clang -x c -fsanitize=implicit-conversion -O0 %s -o %t && %run %t 2>&1 | FileCheck %s --implicit-check-not="implicit conversion" --check-prefixes=CHECK
// RUN: %clang -x c -fsanitize=implicit-conversion -O1 %s -o %t && %run %t 2>&1 | FileCheck %s --implicit-check-not="implicit conversion" --check-prefixes=CHECK
// RUN: %clang -x c -fsanitize=implicit-conversion -O2 %s -o %t && %run %t 2>&1 | FileCheck %s --implicit-check-not="implicit conversion" --check-prefixes=CHECK
// RUN: %clang -x c -fsanitize=implicit-conversion -O3 %s -o %t && %run %t 2>&1 | FileCheck %s --implicit-check-not="implicit conversion" --check-prefixes=CHECK
// RUN: %clang -x c++ -fsanitize=implicit-conversion -O0 %s -o %t && %run %t 2>&1 | FileCheck %s --implicit-check-not="implicit conversion" --check-prefixes=CHECK
// RUN: %clang -x c++ -fsanitize=implicit-conversion -O1 %s -o %t && %run %t 2>&1 | FileCheck %s --implicit-check-not="implicit conversion" --check-prefixes=CHECK
// RUN: %clang -x c++ -fsanitize=implicit-conversion -O2 %s -o %t && %run %t 2>&1 | FileCheck %s --implicit-check-not="implicit conversion" --check-prefixes=CHECK
// RUN: %clang -x c++ -fsanitize=implicit-conversion -O3 %s -o %t && %run %t 2>&1 | FileCheck %s --implicit-check-not="implicit conversion" --check-prefixes=CHECK
void test_unsigned() {
unsigned char x;
x = 0;
x++;
x = 0;
++x;
x = 0;
x--;
// CHECK: {{.*}}integer-conversion-incdec.c:[[@LINE-1]]:4: runtime error: implicit conversion from type 'int' of value -1 (32-bit, signed) to type 'unsigned char' changed the value to 255 (8-bit, unsigned)
x = 0;
--x;
// CHECK: {{.*}}integer-conversion-incdec.c:[[@LINE-1]]:3: runtime error: implicit conversion from type 'int' of value -1 (32-bit, signed) to type 'unsigned char' changed the value to 255 (8-bit, unsigned)
x = 1;
x++;
x = 1;
++x;
x = 1;
x--;
x = 1;
--x;
x = 254;
x++;
x = 254;
++x;
x = 254;
x--;
x = 254;
--x;
x = 255;
x++;
// CHECK: {{.*}}integer-conversion-incdec.c:[[@LINE-1]]:4: runtime error: implicit conversion from type 'int' of value 256 (32-bit, signed) to type 'unsigned char' changed the value to 0 (8-bit, unsigned)
x = 255;
++x;
// CHECK: {{.*}}integer-conversion-incdec.c:[[@LINE-1]]:3: runtime error: implicit conversion from type 'int' of value 256 (32-bit, signed) to type 'unsigned char' changed the value to 0 (8-bit, unsigned)
x = 255;
x--;
x = 255;
--x;
}
void test_signed() {
signed char x;
x = -128;
x++;
x = -128;
++x;
x = -128;
x--;
// CHECK: {{.*}}integer-conversion-incdec.c:[[@LINE-1]]:4: runtime error: implicit conversion from type 'int' of value -129 (32-bit, signed) to type 'signed char' changed the value to 127 (8-bit, signed)
x = -128;
--x;
// CHECK: {{.*}}integer-conversion-incdec.c:[[@LINE-1]]:3: runtime error: implicit conversion from type 'int' of value -129 (32-bit, signed) to type 'signed char' changed the value to 127 (8-bit, signed)
x = -1;
x++;
x = -1;
++x;
x = -1;
x--;
x = -1;
--x;
x = 0;
x++;
x = 0;
++x;
x = 0;
x--;
x = 0;
--x;
x = 1;
x++;
x = 1;
++x;
x = 1;
x--;
x = 1;
--x;
x = 127;
x++;
// CHECK: {{.*}}integer-conversion-incdec.c:[[@LINE-1]]:4: runtime error: implicit conversion from type 'int' of value 128 (32-bit, signed) to type 'signed char' changed the value to -128 (8-bit, signed)
x = 127;
++x;
// CHECK: {{.*}}integer-conversion-incdec.c:[[@LINE-1]]:3: runtime error: implicit conversion from type 'int' of value 128 (32-bit, signed) to type 'signed char' changed the value to -128 (8-bit, signed)
x = 127;
x--;
x = 127;
--x;
}
int main() {
test_unsigned();
test_signed();
return 0;
}