[Clang][NFC] Improve generation of GEP and RecordDecl loop (#101434)

As with other loops, we need only look at a RecordDecl's FieldDecls.
Convert to using them. In the meantime, we can improve the generation of
the 'counted_by' FieldDecl's GEP by creating one GEP instead of a series
of GEPs.

Author: bwendling

clang/lib/CodeGen/CGBuiltin.cpp

@@ -996,7 +996,7 @@ CodeGenFunction::emitFlexibleArrayMemberSize(const Expr *E, unsigned Type,
 
   // Build a load of the counted_by field.
   bool IsSigned = CountedByFD->getType()->isSignedIntegerType();
-  Value *CountedByInst = EmitCountedByFieldExpr(Base, FAMDecl, CountedByFD);
+  Value *CountedByInst = EmitLoadOfCountedByField(Base, FAMDecl, CountedByFD);
   if (!CountedByInst)
     return getDefaultBuiltinObjectSizeResult(Type, ResType);
 

clang/lib/CodeGen/CGExpr.cpp

@@ -1067,8 +1067,7 @@ class StructAccessBase
 
 } // end anonymous namespace
 
-using RecIndicesTy =
-    SmallVector<std::pair<const RecordDecl *, llvm::Value *>, 8>;
+using RecIndicesTy = SmallVector<llvm::Value *, 8>;
 
 static bool getGEPIndicesToField(CodeGenFunction &CGF, const RecordDecl *RD,
                                  const FieldDecl *Field,
@@ -1083,7 +1082,7 @@ static bool getGEPIndicesToField(CodeGenFunction &CGF, const RecordDecl *RD,
 
     FieldNo = Layout.getLLVMFieldNo(FD);
     if (FD == Field) {
-      Indices.emplace_back(std::make_pair(RD, CGF.Builder.getInt32(FieldNo)));
+      Indices.emplace_back(CGF.Builder.getInt32(FieldNo));
       return true;
     }
 
@@ -1092,7 +1091,7 @@ static bool getGEPIndicesToField(CodeGenFunction &CGF, const RecordDecl *RD,
       if (getGEPIndicesToField(CGF, Ty->getAsRecordDecl(), Field, Indices)) {
         if (RD->isUnion())
           FieldNo = 0;
-        Indices.emplace_back(std::make_pair(RD, CGF.Builder.getInt32(FieldNo)));
+        Indices.emplace_back(CGF.Builder.getInt32(FieldNo));
         return true;
       }
     }
@@ -1109,7 +1108,7 @@ static bool getGEPIndicesToField(CodeGenFunction &CGF, const RecordDecl *RD,
 /// - \p FAMDecl: the \p Decl for the flexible array member. It may not be
 ///   within the top-level struct.
 /// - \p CountDecl: must be within the same non-anonymous struct as \p FAMDecl.
-llvm::Value *CodeGenFunction::EmitCountedByFieldExpr(
+llvm::Value *CodeGenFunction::EmitLoadOfCountedByField(
     const Expr *Base, const FieldDecl *FAMDecl, const FieldDecl *CountDecl) {
   const RecordDecl *RD = CountDecl->getParent()->getOuterLexicalRecordContext();
 
@@ -1136,15 +1135,15 @@ llvm::Value *CodeGenFunction::EmitCountedByFieldExpr(
     return nullptr;
   }
 
-  llvm::Value *Zero = Builder.getInt32(0);
   RecIndicesTy Indices;
-
   getGEPIndicesToField(*this, RD, CountDecl, Indices);
+  if (Indices.empty())
+    return nullptr;
 
-  for (auto I = Indices.rbegin(), E = Indices.rend(); I != E; ++I)
-    Res = Builder.CreateInBoundsGEP(
-        ConvertType(QualType(I->first->getTypeForDecl(), 0)), Res,
-        {Zero, I->second}, "..counted_by.gep");
+  Indices.push_back(Builder.getInt32(0));
+  Res = Builder.CreateInBoundsGEP(
+      ConvertType(QualType(RD->getTypeForDecl(), 0)), Res,
+      RecIndicesTy(llvm::reverse(Indices)), "..counted_by.gep");
 
   return Builder.CreateAlignedLoad(ConvertType(CountDecl->getType()), Res,
                                    getIntAlign(), "..counted_by.load");
@@ -4108,25 +4107,25 @@ static Address emitArraySubscriptGEP(CodeGenFunction &CGF, Address addr,
 
 /// The offset of a field from the beginning of the record.
 static bool getFieldOffsetInBits(CodeGenFunction &CGF, const RecordDecl *RD,
-                                 const FieldDecl *FD, int64_t &Offset) {
+                                 const FieldDecl *Field, int64_t &Offset) {
   ASTContext &Ctx = CGF.getContext();
   const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(RD);
   unsigned FieldNo = 0;
 
-  for (const Decl *D : RD->decls()) {
-    if (const auto *Record = dyn_cast<RecordDecl>(D))
-      if (getFieldOffsetInBits(CGF, Record, FD, Offset)) {
-        Offset += Layout.getFieldOffset(FieldNo);
-        return true;
-      }
+  for (const FieldDecl *FD : RD->fields()) {
+    if (FD == Field) {
+      Offset += Layout.getFieldOffset(FieldNo);
+      return true;
+    }
 
-    if (const auto *Field = dyn_cast<FieldDecl>(D))
-      if (FD == Field) {
+    QualType Ty = FD->getType();
+    if (Ty->isRecordType())
+      if (getFieldOffsetInBits(CGF, Ty->getAsRecordDecl(), Field, Offset)) {
         Offset += Layout.getFieldOffset(FieldNo);
         return true;
       }
 
-    if (isa<FieldDecl>(D))
+    if (!RD->isUnion())
       ++FieldNo;
   }
 

clang/lib/CodeGen/CodeGenFunction.h

@@ -3310,9 +3310,9 @@ class CodeGenFunction : public CodeGenTypeCache {
   const FieldDecl *FindCountedByField(const FieldDecl *FD);
 
   /// Build an expression accessing the "counted_by" field.
-  llvm::Value *EmitCountedByFieldExpr(const Expr *Base,
-                                      const FieldDecl *FAMDecl,
-                                      const FieldDecl *CountDecl);
+  llvm::Value *EmitLoadOfCountedByField(const Expr *Base,
+                                        const FieldDecl *FAMDecl,
+                                        const FieldDecl *CountDecl);
 
   llvm::Value *EmitScalarPrePostIncDec(const UnaryOperator *E, LValue LV,
                                        bool isInc, bool isPre);

clang/test/CodeGen/attr-counted-by.c

@@ -754,11 +754,11 @@ size_t test7_bdos(struct union_of_fams *p) {
 // SANITIZE-WITH-ATTR-NEXT:    [[IDXPROM:%.*]] = sext i32 [[INDEX]] to i64
 // SANITIZE-WITH-ATTR-NEXT:    [[TMP0:%.*]] = zext i8 [[DOT_COUNTED_BY_LOAD]] to i64, !nosanitize [[META2]]
 // SANITIZE-WITH-ATTR-NEXT:    [[TMP1:%.*]] = icmp ult i64 [[IDXPROM]], [[TMP0]], !nosanitize [[META2]]
-// SANITIZE-WITH-ATTR-NEXT:    br i1 [[TMP1]], label [[CONT9:%.*]], label [[HANDLER_OUT_OF_BOUNDS:%.*]], !prof [[PROF3]], !nosanitize [[META2]]
+// SANITIZE-WITH-ATTR-NEXT:    br i1 [[TMP1]], label [[CONT7:%.*]], label [[HANDLER_OUT_OF_BOUNDS:%.*]], !prof [[PROF3]], !nosanitize [[META2]]
 // SANITIZE-WITH-ATTR:       handler.out_of_bounds:
 // SANITIZE-WITH-ATTR-NEXT:    tail call void @__ubsan_handle_out_of_bounds_abort(ptr nonnull @[[GLOB12:[0-9]+]], i64 [[IDXPROM]]) #[[ATTR10]], !nosanitize [[META2]]
 // SANITIZE-WITH-ATTR-NEXT:    unreachable, !nosanitize [[META2]]
-// SANITIZE-WITH-ATTR:       cont9:
+// SANITIZE-WITH-ATTR:       cont7:
 // SANITIZE-WITH-ATTR-NEXT:    [[INTS:%.*]] = getelementptr inbounds i8, ptr [[P]], i64 9
 // SANITIZE-WITH-ATTR-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds [0 x i8], ptr [[INTS]], i64 0, i64 [[IDXPROM]]
 // SANITIZE-WITH-ATTR-NEXT:    store i8 [[DOT_COUNTED_BY_LOAD]], ptr [[ARRAYIDX]], align 1, !tbaa [[TBAA8]]
@@ -908,11 +908,11 @@ size_t test9_bdos(struct union_of_fams *p) {
 // SANITIZE-WITH-ATTR-NEXT:    [[IDXPROM:%.*]] = sext i32 [[INDEX]] to i64
 // SANITIZE-WITH-ATTR-NEXT:    [[TMP0:%.*]] = zext i32 [[DOT_COUNTED_BY_LOAD]] to i64, !nosanitize [[META2]]
 // SANITIZE-WITH-ATTR-NEXT:    [[TMP1:%.*]] = icmp ult i64 [[IDXPROM]], [[TMP0]], !nosanitize [[META2]]
-// SANITIZE-WITH-ATTR-NEXT:    br i1 [[TMP1]], label [[CONT9:%.*]], label [[HANDLER_OUT_OF_BOUNDS:%.*]], !prof [[PROF3]], !nosanitize [[META2]]
+// SANITIZE-WITH-ATTR-NEXT:    br i1 [[TMP1]], label [[CONT7:%.*]], label [[HANDLER_OUT_OF_BOUNDS:%.*]], !prof [[PROF3]], !nosanitize [[META2]]
 // SANITIZE-WITH-ATTR:       handler.out_of_bounds:
 // SANITIZE-WITH-ATTR-NEXT:    tail call void @__ubsan_handle_out_of_bounds_abort(ptr nonnull @[[GLOB15:[0-9]+]], i64 [[IDXPROM]]) #[[ATTR10]], !nosanitize [[META2]]
 // SANITIZE-WITH-ATTR-NEXT:    unreachable, !nosanitize [[META2]]
-// SANITIZE-WITH-ATTR:       cont9:
+// SANITIZE-WITH-ATTR:       cont7:
 // SANITIZE-WITH-ATTR-NEXT:    [[BYTES:%.*]] = getelementptr inbounds i8, ptr [[P]], i64 12
 // SANITIZE-WITH-ATTR-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds [0 x i8], ptr [[BYTES]], i64 0, i64 [[IDXPROM]]
 // SANITIZE-WITH-ATTR-NEXT:    [[NARROW:%.*]] = tail call i32 @llvm.smax.i32(i32 [[DOT_COUNTED_BY_LOAD]], i32 0)