[Preamble] Reuse preamble even if an unsaved file does not exist

When a preamble is created an unsaved file not existing on disk is
already part of PrecompiledPreamble::FilesInPreamble. However, when
checking whether the preamble can be re-used, a failed stat of such an
unsaved file invalidated the preamble, which led to pointless and time
consuming preamble regenerations on subsequent reparses.

Do not require anymore that unsaved files should exist on disk.

This avoids costly preamble invalidations depending on timing issues for
the cases where the file on disk might be removed just to be regenerated
a bit later.

It also allows an IDE to provide in-memory files that might not exist on
disk, e.g. because the build system hasn't generated those yet.

Differential Revision: https://reviews.llvm.org/D41005

llvm-svn: 361226

1 files changed, 12 insertions, 10 deletions

diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 221bf97c..95d1bf2 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -1304,22 +1304,22 @@ ASTUnit::getMainBufferWithPrecompiledPreamble(
                             PreambleInvocationIn.getDiagnosticOpts());
       getDiagnostics().setNumWarnings(NumWarningsInPreamble);
 
-      PreambleRebuildCounter = 1;
+      PreambleRebuildCountdown = 1;
       return MainFileBuffer;
     } else {
       Preamble.reset();
       PreambleDiagnostics.clear();
       TopLevelDeclsInPreamble.clear();
       PreambleSrcLocCache.clear();
-      PreambleRebuildCounter = 1;
+      PreambleRebuildCountdown = 1;
     }
   }
 
   // If the preamble rebuild counter > 1, it's because we previously
   // failed to build a preamble and we're not yet ready to try
   // again. Decrement the counter and return a failure.
-  if (PreambleRebuildCounter > 1) {
-    --PreambleRebuildCounter;
+  if (PreambleRebuildCountdown > 1) {
+    --PreambleRebuildCountdown;
     return nullptr;
   }
 
@@ -1329,6 +1329,8 @@ ASTUnit::getMainBufferWithPrecompiledPreamble(
   if (!AllowRebuild)
     return nullptr;
 
+  ++PreambleCounter;
+
   SmallVector<StandaloneDiagnostic, 4> NewPreambleDiagsStandalone;
   SmallVector<StoredDiagnostic, 4> NewPreambleDiags;
   ASTUnitPreambleCallbacks Callbacks;
@@ -1356,18 +1358,18 @@ ASTUnit::getMainBufferWithPrecompiledPreamble(
 
     if (NewPreamble) {
       Preamble = std::move(*NewPreamble);
-      PreambleRebuildCounter = 1;
+      PreambleRebuildCountdown = 1;
     } else {
       switch (static_cast<BuildPreambleError>(NewPreamble.getError().value())) {
       case BuildPreambleError::CouldntCreateTempFile:
         // Try again next time.
-        PreambleRebuildCounter = 1;
+        PreambleRebuildCountdown = 1;
         return nullptr;
       case BuildPreambleError::CouldntCreateTargetInfo:
       case BuildPreambleError::BeginSourceFileFailed:
       case BuildPreambleError::CouldntEmitPCH:
         // These erros are more likely to repeat, retry after some period.
-        PreambleRebuildCounter = DefaultPreambleRebuildInterval;
+        PreambleRebuildCountdown = DefaultPreambleRebuildInterval;
         return nullptr;
       }
       llvm_unreachable("unexpected BuildPreambleError");
@@ -1507,7 +1509,7 @@ ASTUnit *ASTUnit::LoadFromCompilerInvocationAction(
   AST->OnlyLocalDecls = OnlyLocalDecls;
   AST->CaptureDiagnostics = CaptureDiagnostics;
   if (PrecompilePreambleAfterNParses > 0)
-    AST->PreambleRebuildCounter = PrecompilePreambleAfterNParses;
+    AST->PreambleRebuildCountdown = PrecompilePreambleAfterNParses;
   AST->TUKind = Action ? Action->getTranslationUnitKind() : TU_Complete;
   AST->ShouldCacheCodeCompletionResults = CacheCodeCompletionResults;
   AST->IncludeBriefCommentsInCodeCompletion
@@ -1641,7 +1643,7 @@ bool ASTUnit::LoadFromCompilerInvocation(
 
   std::unique_ptr<llvm::MemoryBuffer> OverrideMainBuffer;
   if (PrecompilePreambleAfterNParses > 0) {
-    PreambleRebuildCounter = PrecompilePreambleAfterNParses;
+    PreambleRebuildCountdown = PrecompilePreambleAfterNParses;
     OverrideMainBuffer =
         getMainBufferWithPrecompiledPreamble(PCHContainerOps, *Invocation, VFS);
     getDiagnostics().Reset();
@@ -1819,7 +1821,7 @@ bool ASTUnit::Reparse(std::shared_ptr<PCHContainerOperations> PCHContainerOps,
   // If we have a preamble file lying around, or if we might try to
   // build a precompiled preamble, do so now.
   std::unique_ptr<llvm::MemoryBuffer> OverrideMainBuffer;
-  if (Preamble || PreambleRebuildCounter > 0)
+  if (Preamble || PreambleRebuildCountdown > 0)
     OverrideMainBuffer =
         getMainBufferWithPrecompiledPreamble(PCHContainerOps, *Invocation, VFS);