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[clang][lex] Cache stat failures in -Wshadow-header (#215962)

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The `-Wshadow-header` warning introduced in
https://github.com/llvm/llvm-project/pull/162491 gets enabled by
`-Weverything` and causes `O(H*I*S)` extra `status()` syscalls (where H
is the number of included headers, I is the average number of inclusions
per header, S is the number of search paths). This is caused by
proactively probing search paths even after finding a suitable header,
and calling `FileManager` with `CacheFailure = false`.

There's no reason to not cache the non-existence of header files during
these probes. This PR starts caching these, bringing down the complexity
to `O(H*S)` and adds a regression test.

(cherry picked from commit 5fa5caa0f2f768af54087a3df749990c41c18a04)
This commit is contained in:
Jan Svoboda authored and Douglas Yung committed 2026-08-18 08:11:29 +00:00
1 parent c2347d5252
commit 3cc48bac4b
2 files changed
+24 -2
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clang/lib/Lex/HeaderSearch.cpp
+2 -2
View File
@@ -907,7 +907,7 @@ void HeaderSearch::diagnoseHeaderShadowing(
const auto &IncluderAndDir = Includers[i];
SmallString<1024> TmpDir = IncluderAndDir.second.getName();
llvm::sys::path::append(TmpDir, Filename);
if (auto File = getFileMgr().getOptionalFileRef(TmpDir, false, false)) {
if (auto File = getFileMgr().getOptionalFileRef(TmpDir)) {
if (&File->getFileEntry() == *FE)
continue;
Diags.Report(IncludeLoc, diag::warn_header_shadowing)
@@ -932,7 +932,7 @@ void HeaderSearch::diagnoseHeaderShadowing(
continue;
SmallString<1024> TmpPath = It->getName();
llvm::sys::path::append(TmpPath, Filename);
if (auto File = getFileMgr().getOptionalFileRef(TmpPath, false, false)) {
if (auto File = getFileMgr().getOptionalFileRef(TmpPath)) {
if (&File->getFileEntry() == *FE)
continue;
Diags.Report(IncludeLoc, diag::warn_header_shadowing)
clang/test/Preprocessor/header-shadowing-stats.c
+22
View File
@@ -0,0 +1,22 @@
// This test checks that -Wshadow-header doesn't repeatedly perform the same IO.
// RUN: rm -rf %t
// RUN: split-file %s %t
//--- tu1.c
#include "header.h"
//--- tu2.c
#include "header.h"
// The following line should not trigger more IO:
#include "header.h"
//--- include1/header.h
//--- include2/keep.h
// RUN: %clang_cc1 -Eonly %t/tu1.c -I %t/include1 -I %t/include2 -Wshadow-header -print-stats 2>%t/tu1.stats
// RUN: %clang_cc1 -Eonly %t/tu2.c -I %t/include1 -I %t/include2 -Wshadow-header -print-stats 2>%t/tu2.stats
// RUN: cat %t/tu1.stats %t/tu2.stats | FileCheck %s
// CHECK: *** Virtual File System Stats:
// CHECK-NEXT: [[STATUS_COUNT:[0-9]+]] status() calls
// CHECK: *** Virtual File System Stats:
// CHECK-NEXT: [[STATUS_COUNT]] status() calls