Add a new altera check for structure packing and alignment.
The altera struct pack align lint check finds structs that are inefficiently
packed or aligned and recommends packing/aligning of the structs using the
packed and aligned attributes as needed in a warning.
diff --git a/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp b/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp
new file mode 100644
index 0000000..9f28a22
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp
@@ -0,0 +1,144 @@
+//===--- StructPackAlignCheck.cpp - clang-tidy ----------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "StructPackAlignCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/RecordLayout.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include <math.h>
+#include <sstream>
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace altera {
+
+void StructPackAlignCheck::registerMatchers(MatchFinder *Finder) {
+ Finder->addMatcher(recordDecl(isStruct(), isDefinition(),
+ unless(isExpansionInSystemHeader()))
+ .bind("struct"),
+ this);
+}
+
+CharUnits
+StructPackAlignCheck::computeRecommendedAlignment(CharUnits MinByteSize) {
+ CharUnits NewAlign = CharUnits::fromQuantity(1);
+ if (!MinByteSize.isPowerOfTwo()) {
+ int MSB = (int)MinByteSize.getQuantity();
+ for (; MSB > 0; MSB /= 2) {
+ NewAlign = NewAlign.alignTo(
+ CharUnits::fromQuantity(((int)NewAlign.getQuantity()) * 2));
+ // Abort if the computed alignment meets the maximum configured alignment.
+ if (NewAlign.getQuantity() >= MaxConfiguredAlignment)
+ break;
+ }
+ } else {
+ NewAlign = MinByteSize;
+ }
+ return NewAlign;
+}
+
+void StructPackAlignCheck::check(const MatchFinder::MatchResult &Result) {
+ const auto *Struct = Result.Nodes.getNodeAs<RecordDecl>("struct");
+
+ // Do not trigger on templated struct declarations because the packing and
+ // alignment requirements are unknown.
+ if (Struct->isTemplated())
+ return;
+
+ // Get sizing info for the struct.
+ llvm::SmallVector<std::pair<unsigned int, unsigned int>, 10> FieldSizes;
+ unsigned int TotalBitSize = 0;
+ for (const FieldDecl *StructField : Struct->fields()) {
+ // For each StructField, record how big it is (in bits).
+ // Would be good to use a pair of <offset, size> to advise a better
+ // packing order.
+ unsigned int StructFieldWidth =
+ (unsigned int)Result.Context
+ ->getTypeInfo(StructField->getType().getTypePtr())
+ .Width;
+ FieldSizes.emplace_back(StructFieldWidth, StructField->getFieldIndex());
+ // FIXME: Recommend a reorganization of the struct (sort by StructField
+ // size, largest to smallest).
+ TotalBitSize += StructFieldWidth;
+ }
+
+ uint64_t CharSize = Result.Context->getCharWidth();
+ CharUnits CurrSize = Result.Context->getASTRecordLayout(Struct).getSize();
+ CharUnits MinByteSize =
+ CharUnits::fromQuantity(ceil((float)TotalBitSize / CharSize));
+ CharUnits MaxAlign = CharUnits::fromQuantity(
+ ceil((float)Struct->getMaxAlignment() / CharSize));
+ CharUnits CurrAlign =
+ Result.Context->getASTRecordLayout(Struct).getAlignment();
+ CharUnits NewAlign = computeRecommendedAlignment(MinByteSize);
+
+ bool IsPacked = Struct->hasAttr<PackedAttr>();
+ bool NeedsPacking = (MinByteSize < CurrSize) && (MaxAlign != NewAlign) &&
+ (CurrSize != NewAlign);
+ bool NeedsAlignment = CurrAlign.getQuantity() != NewAlign.getQuantity();
+
+ if (!NeedsAlignment && !NeedsPacking)
+ return;
+
+ // If it's using much more space than it needs, suggest packing.
+ // (Do not suggest packing if it is currently explicitly aligned to what the
+ // minimum byte size would suggest as the new alignment.)
+ if (NeedsPacking && !IsPacked) {
+ diag(Struct->getLocation(),
+ "accessing fields in struct %0 is inefficient due to padding; only "
+ "needs %1 bytes but is using %2 bytes")
+ << Struct << (int)MinByteSize.getQuantity()
+ << (int)CurrSize.getQuantity()
+ << FixItHint::CreateInsertion(Struct->getEndLoc().getLocWithOffset(1),
+ " __attribute__((packed))");
+ diag(Struct->getLocation(),
+ "use \"__attribute__((packed))\" to reduce the amount of padding "
+ "applied to struct %0",
+ DiagnosticIDs::Note)
+ << Struct;
+ }
+
+ FixItHint FixIt;
+ AlignedAttr *Attribute = Struct->getAttr<AlignedAttr>();
+ std::string NewAlignQuantity = std::to_string((int)NewAlign.getQuantity());
+ if (Attribute) {
+ std::ostringstream FixItString;
+ FixItString << "aligned(" << NewAlignQuantity << ")";
+ FixIt =
+ FixItHint::CreateReplacement(Attribute->getRange(), FixItString.str());
+ } else {
+ std::ostringstream FixItString;
+ FixItString << " __attribute__((aligned(" << NewAlignQuantity << ")))";
+ FixIt = FixItHint::CreateInsertion(Struct->getEndLoc().getLocWithOffset(1),
+ FixItString.str());
+ }
+
+ // And suggest the minimum power-of-two alignment for the struct as a whole
+ // (with and without packing).
+ if (NeedsAlignment) {
+ diag(Struct->getLocation(),
+ "accessing fields in struct %0 is inefficient due to poor alignment; "
+ "currently aligned to %1 bytes, but recommended alignment is %2 bytes")
+ << Struct << (int)CurrAlign.getQuantity() << NewAlignQuantity << FixIt;
+
+ diag(Struct->getLocation(),
+ "use \"__attribute__((aligned(%0)))\" to align struct %1 to %0 bytes",
+ DiagnosticIDs::Note)
+ << NewAlignQuantity << Struct;
+ }
+}
+
+void StructPackAlignCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+ Options.store(Opts, "MaxConfiguredAlignment", MaxConfiguredAlignment);
+}
+
+} // namespace altera
+} // namespace tidy
+} // namespace clang
