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[LTO] Fix assertion failed when flushing bitcode incrementally for LTO output. 

In https://reviews.llvm.org/D86905, we introduce an optimization, when lld emits LLVM bitcode,
we allow bitcode writer flush data to disk early when buffered data size is above some threshold.

But when `--plugin-opt=emit-llvm` and `-o /dev/null` are used,
lld will trigger assertion `BytesRead >= 0 && static_cast<size_t>(BytesRead) == BytesFromDisk`.
When we write output to /dev/null, BytesRead is zero, but at this program point BytesFromDisk is always non-zero.

Reviewed By: stephan.yichao.zhao, MaskRay

Differential Revision: https://reviews.llvm.org/D112297
This commit is contained in:
Xu Mingjie 2022-01-04 21:40:23 -08:00 committed by Fangrui Song
parent 2899e8de67
commit b5149f4e66
3 changed files with 13 additions and 6 deletions
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4
lld/test/ELF/lto/emit-llvm.ll
View File

@ -4,6 +4,10 @@
; RUN: ld.lld --plugin-opt=emit-llvm -o %t.out.o %t.o
; RUN: llvm-dis < %t.out.o -o - | FileCheck %s
;; Regression test for D112297: bitcode writer used to crash when
;; --plugin-opt=emit-llvmis enabled and the output is /dev/null.
; RUN: ld.lld --plugin-opt=emit-llvm -mllvm -bitcode-flush-threshold=0 -o /dev/null %t.o
; CHECK: define internal void @main()
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"

3
llvm/include/llvm/Support/raw_ostream.h
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@ -444,6 +444,7 @@ class raw_fd_ostream : public raw_pwrite_stream {
int FD;
bool ShouldClose;
bool SupportsSeeking = false;
bool IsRegularFile = false;
mutable Optional<bool> HasColors;
#ifdef _WIN32
@ -514,6 +515,8 @@ public:
bool supportsSeeking() const { return SupportsSeeking; }
bool isRegularFile() const { return IsRegularFile; }
/// Flushes the stream and repositions the underlying file descriptor position
/// to the offset specified from the beginning of the file.
uint64_t seek(uint64_t off);

12
llvm/lib/Support/raw_ostream.cpp
View File

@ -643,13 +643,14 @@ raw_fd_ostream::raw_fd_ostream(int fd, bool shouldClose, bool unbuffered,
// Get the starting position.
off_t loc = ::lseek(FD, 0, SEEK_CUR);
#ifdef _WIN32
// MSVCRT's _lseek(SEEK_CUR) doesn't return -1 for pipes.
sys::fs::file_status Status;
std::error_code EC = status(FD, Status);
SupportsSeeking = !EC && Status.type() == sys::fs::file_type::regular_file;
IsRegularFile = Status.type() == sys::fs::file_type::regular_file;
#ifdef _WIN32
// MSVCRT's _lseek(SEEK_CUR) doesn't return -1 for pipes.
SupportsSeeking = !EC && IsRegularFile;
#else
SupportsSeeking = loc != (off_t)-1;
SupportsSeeking = !EC && loc != (off_t)-1;
#endif
if (!SupportsSeeking)
pos = 0;
@ -914,8 +915,7 @@ raw_fd_stream::raw_fd_stream(StringRef Filename, std::error_code &EC)
if (EC)
return;
// Do not support non-seekable files.
if (!supportsSeeking())
if (!isRegularFile())
EC = std::make_error_code(std::errc::invalid_argument);
}