[llvm-branch-commits] [clang] 275f30d - [clang] Change builtin object size when subobject is invalid

[George Burgess IV via llvm-branch-commits]

Author: Jeffrey T Mott
Date: 2021-01-07T12:34:07-08:00
New Revision: 275f30df8ad6de75e1f29e4b33eaeb67686caf0d

URL: https://github.com/llvm/llvm-project/commit/275f30df8ad6de75e1f29e4b33eaeb67686caf0d
DIFF: https://github.com/llvm/llvm-project/commit/275f30df8ad6de75e1f29e4b33eaeb67686caf0d.diff

LOG: [clang] Change builtin object size when subobject is invalid

Motivating example:

```
  struct { int v[10]; } t[10];

  __builtin_object_size(
      &t[0].v[11], // access past end of subobject
      1            // request remaining bytes of closest surrounding
                   // subobject
  );
```

In GCC, this returns 0. https://godbolt.org/z/7TeGs7

In current clang, however, this returns 356, the number of bytes
remaining in the whole variable, as if the `type` was 0 instead of 1.
https://godbolt.org/z/6Kffox

This patch checks for the specific case where we're requesting a
subobject's size (type 1) but the subobject is invalid.

Differential Revision: https://reviews.llvm.org/D92892

Added: 
    

Modified: 
    clang/lib/AST/ExprConstant.cpp
    clang/test/CodeGen/object-size.c

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 56181bbe1166..b153e22259f7 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -11408,9 +11408,9 @@ static bool tryEvaluateBuiltinObjectSize(const Expr *E, unsigned Type,
       return false;
   }
 
-  // If we point to before the start of the object, there are no accessible
-  // bytes.
-  if (LVal.getLValueOffset().isNegative()) {
+  // If we point outside of the object, there are no accessible bytes.
+  if (LVal.getLValueOffset().isNegative() ||
+      ((Type & 1) && !LVal.Designator.isValidSubobject())) {
     Size = 0;
     return true;
   }

diff  --git a/clang/test/CodeGen/object-size.c b/clang/test/CodeGen/object-size.c
index ff54b11a0f04..dbf286138454 100644
--- a/clang/test/CodeGen/object-size.c
+++ b/clang/test/CodeGen/object-size.c
@@ -310,7 +310,7 @@ void test24() {
 void test25() {
   // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* {{.*}}, i1 false, i1 true, i1
   gi = OBJECT_SIZE_BUILTIN((void*)0x1000, 0);
-  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* {{.*}}, i1 false, i1 true, i1
+  // CHECK: store i32 0
   gi = OBJECT_SIZE_BUILTIN((void*)0x1000, 1);
   // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* {{.*}}, i1 true, i1 true, i1
   gi = OBJECT_SIZE_BUILTIN((void*)0x1000, 2);
@@ -321,7 +321,7 @@ void test25() {
 
   // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* {{.*}}, i1 false, i1 true, i1
   gi = OBJECT_SIZE_BUILTIN((void*)0 + 0x1000, 0);
-  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* {{.*}}, i1 false, i1 true, i1
+  // CHECK: store i32 0
   gi = OBJECT_SIZE_BUILTIN((void*)0 + 0x1000, 1);
   // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* {{.*}}, i1 true, i1 true, i1
   gi = OBJECT_SIZE_BUILTIN((void*)0 + 0x1000, 2);
@@ -337,7 +337,7 @@ void test26() {
 
   // CHECK: store i32 316
   gi = OBJECT_SIZE_BUILTIN(&t[1].v[11], 0);
-  // CHECK: store i32 312
+  // CHECK: store i32 0
   gi = OBJECT_SIZE_BUILTIN(&t[1].v[12], 1);
   // CHECK: store i32 308
   gi = OBJECT_SIZE_BUILTIN(&t[1].v[13], 2);
@@ -433,7 +433,7 @@ void test29(struct DynStructVar *dv, struct DynStruct0 *d0,
 
   // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 false, i1 true, i1
   gi = OBJECT_SIZE_BUILTIN(d0->snd, 0);
-  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 false, i1 true, i1
+  // CHECK: store i32 0
   gi = OBJECT_SIZE_BUILTIN(d0->snd, 1);
   // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 true, i1 true, i1
   gi = OBJECT_SIZE_BUILTIN(d0->snd, 2);
@@ -518,7 +518,7 @@ void test31() {
   // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 false, i1 true, i1
   gi = OBJECT_SIZE_BUILTIN(&ds1[9].snd[0], 1);
 
-  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 false, i1 true, i1
+  // CHECK: store i32 0
   gi = OBJECT_SIZE_BUILTIN(&ds0[9].snd[0], 1);
 
   // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 false, i1 true, i1