Author: serge-sans-paille Date: 2020-05-25T17:17:29+02:00 New Revision: 7c298c104bfe725d4315926a656263e8a5ac3054
URL: https://github.com/llvm/llvm-project/commit/7c298c104bfe725d4315926a656263e8a5ac3054 DIFF: https://github.com/llvm/llvm-project/commit/7c298c104bfe725d4315926a656263e8a5ac3054.diff LOG: [PGO] Fix computation of function Hash Previous implementation was incorrectly passing an uint64_t, that got converted to an uint8_t, to finalize the hash computation. This led to different functions having the same hash if they only differ by the remaining statements, which is incorrect. Added a new test case that trivially tests that a small function change is reflected in the hash value. Not that as this patch fixes the hash computation, it invalidates all hashes computed before that patch applies, which could be an issue for large build system that pre-compute the profile data and let client download them as part of the build process. Differential Revision: https://reviews.llvm.org/D79961 Added: clang/test/Profile/c-collision.c Modified: clang/lib/CodeGen/CodeGenPGO.cpp Removed: ################################################################################ diff --git a/clang/lib/CodeGen/CodeGenPGO.cpp b/clang/lib/CodeGen/CodeGenPGO.cpp index 3c91a04d5464..98827bc3eec5 100644 --- a/clang/lib/CodeGen/CodeGenPGO.cpp +++ b/clang/lib/CodeGen/CodeGenPGO.cpp @@ -747,13 +747,15 @@ uint64_t PGOHash::finalize() { return Working; // Check for remaining work in Working. - if (Working) - MD5.update(Working); + if (Working) { + using namespace llvm::support; + uint64_t Swapped = endian::byte_swap<uint64_t, little>(Working); + MD5.update(llvm::makeArrayRef((uint8_t *)&Swapped, sizeof(Swapped))); + } // Finalize the MD5 and return the hash. llvm::MD5::MD5Result Result; MD5.final(Result); - using namespace llvm::support; return Result.low(); } diff --git a/clang/test/Profile/c-collision.c b/clang/test/Profile/c-collision.c new file mode 100644 index 000000000000..fabecd752b4e --- /dev/null +++ b/clang/test/Profile/c-collision.c @@ -0,0 +1,22 @@ +// Test that a slight change in the code leads to a diff erent hash. +// RUN: %clang_cc1 -UEXTRA -triple x86_64-unknown-linux-gnu -main-file-name c-collision.c %s -o - -emit-llvm -fprofile-instrument=clang | FileCheck %s --check-prefix=CHECK-NOEXTRA +// RUN: %clang_cc1 -DEXTRA -triple x86_64-unknown-linux-gnu -main-file-name c-collision.c %s -o - -emit-llvm -fprofile-instrument=clang | FileCheck %s --check-prefix=CHECK-EXTRA + +// CHECK-NOEXTRA: @__profd_foo = private global { {{.*}} } { i64 6699318081062747564, i64 7156072912471487002, +// CHECK-EXTRA: @__profd_foo = private global { {{.*}} } { i64 6699318081062747564, i64 -4383447408116050035, + +extern int bar; +void foo() { + if (bar) { + } + if (bar) { + } + if (bar) { + if (bar) { +#ifdef EXTRA + if (bar) { + } +#endif + } + } +} _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
