[PATCH] D138657: [analyzer] Consider single-elem arrays as FAMs by default

[Balázs Benics via Phabricator via cfe-commits]

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According to my measurement in https://reviews.llvm.org/D108230#3933232,
it seems like there is no drawback to enabling this analyzer-config by default.

Actually, enabling this by default would make it consistent with the
codegen of clang, which according to `-fstrict-flex-arrays`, assumes
by default that all trailing arrays could be FAMs, let them be of size
undefined, zero, one, or anything else.

Speaking of `-fstrict-flex-arrays`, in the next patch I'll deprecate
the analyzer-config FAM option in favor of that flag. That way, CSA will
always be in sync with what the codegen will think of FAMs.

So, if a new codebase sets `-fstrict-flex-arrays` to some value above 0,
CSA will also make sure that only arrays of the right size will be
considered as FAMs.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D138657

Files:
  clang/docs/ReleaseNotes.rst
  clang/include/clang/StaticAnalyzer/Core/AnalyzerOptions.def
  clang/test/Analysis/analyzer-config.c
  clang/test/Analysis/flexible-array-members.c


Index: clang/test/Analysis/flexible-array-members.c
===================================================================
--- clang/test/Analysis/flexible-array-members.c
+++ clang/test/Analysis/flexible-array-members.c
@@ -1,13 +1,22 @@
-// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c90
-// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c99
-// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c11
-// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c17
-
-// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++98 -x c++
-// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++03 -x c++
-// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++11 -x c++
-// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++14 -x c++
-// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++17 -x c++
+// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c90 \
+// RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=false
+// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c99 \
+// RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=false
+// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c11 \
+// RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=false
+// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c17 \
+// RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=false
+
+// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++98 -x c++ \
+// RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=false
+// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++03 -x c++ \
+// RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=false
+// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++11 -x c++ \
+// RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=false
+// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++14 -x c++ \
+// RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=false
+// RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c++17 -x c++ \
+// RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=false
 
 // RUN: %clang_analyze_cc1 -triple x86_64-linux-gnu -analyzer-checker=core,unix,debug.ExprInspection %s -verify -std=c17 \
 // RUN:    -analyzer-config consider-single-element-arrays-as-flexible-array-members=true -DSINGLE_ELEMENT_FAMS
Index: clang/test/Analysis/analyzer-config.c
===================================================================
--- clang/test/Analysis/analyzer-config.c
+++ clang/test/Analysis/analyzer-config.c
@@ -33,7 +33,7 @@
 // CHECK-NEXT: cfg-rich-constructors = true
 // CHECK-NEXT: cfg-scopes = false
 // CHECK-NEXT: cfg-temporary-dtors = true
-// CHECK-NEXT: consider-single-element-arrays-as-flexible-array-members = false
+// CHECK-NEXT: consider-single-element-arrays-as-flexible-array-members = true
 // CHECK-NEXT: core.CallAndMessage:ArgInitializedness = true
 // CHECK-NEXT: core.CallAndMessage:ArgPointeeInitializedness = false
 // CHECK-NEXT: core.CallAndMessage:CXXDeallocationArg = true
Index: clang/include/clang/StaticAnalyzer/Core/AnalyzerOptions.def
===================================================================
--- clang/include/clang/StaticAnalyzer/Core/AnalyzerOptions.def
+++ clang/include/clang/StaticAnalyzer/Core/AnalyzerOptions.def
@@ -332,7 +332,7 @@
     "Consider single element arrays as flexible array member candidates. "
     "This will prevent the analyzer from assuming that a single element array "
     "holds a single element.",
-    false)
+    true)
 
 ANALYZER_OPTION(
     bool, ShouldAssumeControlledEnvironment, "assume-controlled-environment",
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -827,6 +827,10 @@
   ``scanbuild`` was also updated accordingly.
   Passing these flags will result in a hard error.
 
+- Trailing array objects of structs with single elements will be considered
+  as flexible-array-members. Use ``-fstrict-flex-array=<N>`` to define
+  what should be considered as flexible-array-member if needed.
+
 .. _release-notes-sanitizers:
 
 Sanitizers


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