[PATCH] Adding checker to detect excess padding in records
The intent of this checker is to generate a report for any class / structure
that could reduce its padding by reordering the fields. This results in a very
noisy checker. To reduce the noise, this checker will currently only warn when
the number of bytes over "optimal" is more than 24. This value is configurable
with -analyzer-config performance.Padding:AllowedPad=N. Small values of
AllowedPad have the potential to generate hundreds of reports, and gigabytes
of HTML reports.
The checker searches for padding violations in two main ways. First, it goes
record by record. A report is generated if the fields could be reordered in a
way that reduces the padding by more than AllowedPad bytes. Second, the
checker will generate a report if an array will cause more than AllowedPad
padding bytes to be generated.
The record checker currently skips many ABI specific cases. Classes with base
classes are skipped because base class tail padding is ABI specific. Bitfields
are just plain hard, and duplicating that code seems like a bad idea. VLAs are
both uncommon and non-trivial to fix.
The array checker isn't very thorough right now. It only checks to see if the
element type's fields could be reordered, and it doesn't recursively check to
see if any of the fields' fields could be reordered. At some point in the
future, it would be nice if "arrays" could also look at array new usages and
malloc patterns that appear to be creating arrays.
llvm-svn: 255545
diff --git a/clang/test/Analysis/padding_c.c b/clang/test/Analysis/padding_c.c
new file mode 100644
index 0000000..ff532c6
--- /dev/null
+++ b/clang/test/Analysis/padding_c.c
@@ -0,0 +1,243 @@
+// RUN: %clang_cc1 -analyze -analyzer-checker=optin.performance -analyzer-config optin.performance.Padding:AllowedPad=2 -verify %s
+
+#if __has_include(<stdalign.h>)
+#include <stdalign.h>
+#endif
+
+#if __has_include(<stdalign.h>) || defined(__cplusplus)
+// expected-warning@+1{{Excessive padding in 'struct FieldAttrAlign' (6 padding}}
+struct FieldAttrAlign {
+ char c1;
+ alignas(4) int i;
+ char c2;
+};
+
+// expected-warning@+1{{Excessive padding in 'struct FieldAttrOverAlign' (10 padding}}
+struct FieldAttrOverAlign {
+ char c1;
+ alignas(8) int i;
+ char c2;
+};
+
+#endif // __has_include(<stdalign.h>) || defined(__cplusplus)
+
+// Re-ordering members of these structs won't reduce padding, so don't warn
+struct LeadingChar { // no-warning
+ char c;
+ int i;
+};
+
+struct TrailingChar { // no-warning
+ int i;
+ char c;
+};
+
+struct Helpless { // no-warning
+ struct TrailingChar i1;
+ struct LeadingChar i2;
+ char c;
+};
+
+#pragma pack(push)
+#pragma pack(1)
+struct SquishedIntSandwich { // no-warning
+ char c1;
+ int i;
+ char c2;
+};
+#pragma pack(pop)
+
+// Re-ordering members of these structs will reduce padding, so warn
+struct IntSandwich { // expected-warning{{Excessive padding in 'struct IntSandwich'}}
+ char c1;
+ int i;
+ char c2;
+};
+
+struct TurDuckHen { // expected-warning{{Excessive padding in 'struct TurDuckHen'}}
+ char c1;
+ struct IntSandwich i;
+ char c2;
+};
+
+#pragma pack(push)
+#pragma pack(2)
+struct SmallIntSandwich { // expected-warning{{Excessive padding in 'struct SmallIntSandwich'}}
+ char c1;
+ int i1;
+ char c2;
+ int i2;
+ char c3;
+ int i3;
+ char c4;
+};
+#pragma pack(pop)
+
+union SomeUnion { // no-warning
+ char c;
+ short s;
+ int i;
+};
+
+struct HoldsAUnion { // expected-warning{{Excessive padding in 'struct HoldsAUnion'}}
+ char c1;
+ union SomeUnion u;
+ char c2;
+};
+
+struct BigCharArray { // no-warning
+ char c[129];
+};
+
+struct SmallCharArray { // no-warning
+ char c[5];
+};
+
+struct MediumIntArray { // no-warning
+ int i[5];
+};
+
+struct LargeSizeToSmallSize { // expected-warning{{Excessive padding in 'struct LargeSizeToSmallSize'}}
+ struct BigCharArray b;
+ struct MediumIntArray m;
+ struct SmallCharArray s;
+};
+
+struct LargeAlignToSmallAlign { // no-warning
+ struct MediumIntArray m;
+ struct BigCharArray b;
+ struct SmallCharArray s;
+};
+
+// Currently ignoring VLA padding problems. Still need to make sure we don't
+// choke on VLAs though
+struct HoldsVLA { // no-warning
+ char c1;
+ int x;
+ char c2;
+ int vla[];
+};
+
+// Currently ignoring bitfield padding problems. Still need to make sure we
+// don't choke on bitfields though
+struct HoldsBitfield { // no-warning
+ char c1;
+ int x;
+ char c2;
+ unsigned char b1 : 3;
+ unsigned char b2 : 3;
+ unsigned char b3 : 2;
+};
+
+typedef struct { // expected-warning{{Excessive padding in 'TypedefSandwich'}}
+ char c1;
+ int i;
+ char c2;
+} TypedefSandwich;
+
+// expected-warning@+1{{Excessive padding in 'struct StructAttrAlign' (10 padding}}
+struct StructAttrAlign {
+ char c1;
+ int i;
+ char c2;
+} __attribute__((aligned(8)));
+
+struct CorrectOverlyAlignedChar { // no-warning
+ char c __attribute__((aligned(4096)));
+ char c1;
+ int x1;
+ char c2;
+ int x2;
+ char c3;
+};
+
+struct OverlyAlignedChar { // expected-warning{{Excessive padding in 'struct OverlyAlignedChar'}}
+ char c1;
+ int x;
+ char c2;
+ char c __attribute__((aligned(4096)));
+};
+
+struct HoldsOverlyAlignedChar { // expected-warning{{Excessive padding in 'struct HoldsOverlyAlignedChar'}}
+ char c1;
+ struct OverlyAlignedChar o;
+ char c2;
+};
+
+void internalStructFunc() {
+ struct X { // expected-warning{{Excessive padding in 'struct X'}}
+ char c1;
+ int t;
+ char c2;
+ };
+ struct X obj;
+}
+
+void typedefStructFunc() {
+ typedef struct { // expected-warning{{Excessive padding in 'S'}}
+ char c1;
+ int t;
+ char c2;
+ } S;
+ S obj;
+}
+
+void anonStructFunc() {
+ struct { // expected-warning{{Excessive padding in 'struct (anonymous}}
+ char c1;
+ int t;
+ char c2;
+ } obj;
+}
+
+// expected-warning@+1{{Excessive padding in 'struct DefaultAttrAlign'}}
+struct DefaultAttrAlign {
+ char c1;
+ long long i;
+ char c2;
+} __attribute__((aligned));
+
+struct CorrectDefaultAttrAlign { // no-warning
+ long long i;
+ char c1;
+ char c2;
+} __attribute__((aligned));
+
+struct TooSmallShortSandwich { // no-warning
+ char c1;
+ short s;
+ char c2;
+};
+
+// expected-warning@+1{{Excessive padding in 'struct SmallArrayShortSandwich'}}
+struct SmallArrayShortSandwich {
+ char c1;
+ short s;
+ char c2;
+} ShortArray[20];
+
+// expected-warning@+1{{Excessive padding in 'struct SmallArrayInFunc'}}
+struct SmallArrayInFunc {
+ char c1;
+ short s;
+ char c2;
+};
+
+void arrayHolder() {
+ struct SmallArrayInFunc Arr[15];
+}
+
+// xxxexpected-warning@+1{{Excessive padding in 'struct SmallArrayInStruct'}}
+struct SmallArrayInStruct {
+ char c1;
+ short s;
+ char c2;
+};
+
+struct HoldsSmallArray {
+ struct SmallArrayInStruct Field[20];
+} HoldsSmallArrayElt;
+
+void nestedPadding() {
+ struct HoldsSmallArray Arr[15];
+}