While casting an (integral) pointer to an integer is obvious - you just get
the integral value of the pointer, casting an integer to an (integral) pointer
is deceivingly different. While you will get a pointer with that integral value,
if you got that integral value via a pointer-to-integer cast originally,
the new pointer will lack the provenance information from the original pointer.
So while (integral) pointer to integer casts are effectively no-ops,
and are transparent to the optimizer, integer to (integral) pointer casts
are *NOT* transparent, and may conceal information from optimizer.
While that may be the intention, it is not always so. For example,
let's take a look at a routine to align the pointer up to the multiple of 16:
The obvious, naive implementation for that is:
```
char* src(char* maybe_underbiased_ptr) {
uintptr_t maybe_underbiased_intptr = (uintptr_t)maybe_underbiased_ptr;
uintptr_t aligned_biased_intptr = maybe_underbiased_intptr + 15;
uintptr_t aligned_intptr = aligned_biased_intptr & (~15);
return (char*)aligned_intptr; // warning: avoid integer to pointer casts [misc-no-inttoptr]
}
```
The check will rightfully diagnose that cast.
But when provenance concealment is not the goal of the code, but an accident,
this example can be rewritten as follows, without using integer to pointer cast:
```
char*
tgt(char* maybe_underbiased_ptr) {
uintptr_t maybe_underbiased_intptr = (uintptr_t)maybe_underbiased_ptr;
uintptr_t aligned_biased_intptr = maybe_underbiased_intptr + 15;
uintptr_t aligned_intptr = aligned_biased_intptr & (~15);
uintptr_t bias = aligned_intptr - maybe_underbiased_intptr;
return maybe_underbiased_ptr + bias;
}
```
See also:
* D71499
* [[ https://www.cs.utah.edu/~regehr/oopsla18.pdf | Juneyoung Lee, Chung-Kil Hur, Ralf Jung, Zhengyang Liu, John Regehr, and Nuno P. Lopes. 2018. Reconciling High-Level Optimizations and Low-Level Code in LLVM. Proc. ACM Program. Lang. 2, OOPSLA, Article 125 (November 2018), 28 pages. ]]
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D91055
Checks for types which can be made trivially-destructible by removing
out-of-line defaulted destructor declarations.
The check is motivated by the work on C++ garbage collector in Blink
(rendering engine for Chrome), which strives to minimize destructors and
improve runtime of sweeping phase.
In the entire chromium codebase the check hits over 2000 times.
Differential Revision: https://reviews.llvm.org/D69435
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
Summary:
This patch renames checks, check options and changes messages to use correct
term "implicit conversion" instead of "implicit cast" (which has been in use in
Clang AST since ~10 years, but it's still technically incorrect w.r.t. C++
standard).
* performance-implicit-cast-in-loop -> performance-implicit-conversion-in-loop
* readability-implicit-bool-cast -> readability-implicit-bool-conversion
- readability-implicit-bool-cast.AllowConditionalIntegerCasts ->
readability-implicit-bool-conversion.AllowIntegerConditions
- readability-implicit-bool-cast.AllowConditionalPointerCasts ->
readability-implicit-bool-conversion.AllowPointerConditions
Reviewers: hokein, jdennett
Reviewed By: hokein
Subscribers: mgorny, JDevlieghere, xazax.hun, cfe-commits
Differential Revision: https://reviews.llvm.org/D36456
llvm-svn: 310366
Summary:
The "performance-inefficient-vector-operation" check finds vector oprations in
for-loop statements which may cause multiple memory reallocations.
This is the first version, only detects typical for-loop:
```
std::vector<int> v;
for (int i = 0; i < n; ++i) {
v.push_back(i);
}
// or
for (int i = 0; i < v2.size(); ++i) {
v.push_back(v2[i]);
}
```
We can extend it to handle more cases like for-range loop in the future.
Reviewers: alexfh, aaron.ballman
Reviewed By: aaron.ballman
Subscribers: zaks.anna, Eugene.Zelenko, mgorny, cfe-commits, djasper
Differential Revision: https://reviews.llvm.org/D31757
llvm-svn: 300534
Summary:
This checks for calls to double-precision math.h with single-precision
arguments. For example, it suggests replacing ::sin(0.f) with
::sinf(0.f).
Subscribers: mgorny, cfe-commits
Differential Revision: https://reviews.llvm.org/D27284
llvm-svn: 289627
Summary:
Add check performance-faster-string-find.
It replaces single character string literals to character literals in calls to string::find and friends.
Reviewers: alexfh
Subscribers: cfe-commits
Differential Revision: http://reviews.llvm.org/D16152
llvm-svn: 260712
Summary: This is implemented originally by Alex Pilkiewicz (pilki@google.com).
Reviewers: alexfh
Subscribers: cfe-commits
Patch by Haojian Wu!
Differential Revision: http://reviews.llvm.org/D16721
llvm-svn: 259195
Summary:
The patch adds a new ClangTidy check that detects when expensive-to-copy types are unnecessarily copy initialized from a const reference that has the same or are larger scope than the copy.
It currently only detects this when the copied variable is const qualified. But this will be extended to non const variables if they are only used in a const fashion.
Reviewers: alexfh
Subscribers: cfe-commits
Patch by Felix Berger!
Differential Revision: http://reviews.llvm.org/D15623
llvm-svn: 256632
Roman Lebedev