yonghong-song created this revision.
yonghong-song added reviewers: ast, anakryiko.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.
The patch is still work in progress.
The signature:
u64 __builtin_bitfield_info(bitfield_member_access)
return value:
ret >> 16 : bitfield offset from the start of the struct
(ret >> 15) & 0x1 : bitfield signness
ret & (1 << 15 - 1) : bitfield size
The information is extracted from:
https://clang.llvm.org/doxygen/structclang_1_1CodeGen_1_1CGBitFieldInfo.html
An example:
-bash-4.4$ cat bit.c
struct s {
int a;
long long p1;
int p2;
int b1:2;
int b2:10;
int b3:2;
int b4:10;
int b5:3;
int d;
};
struct s *a;
int main () {
unsigned long long x = __builtin_bitfield_info(a->b3);
printf("offset = %lld, sign = %lld, size = %lld\n",
x >> 16, (x >> 15) & 1, x & ((1 << 15) - 1));
return 0;
}
-bash-4.4$ clang -O2 -g bit.c
-bash-4.4$ ./a.out
offset = 172, sign = 1, size = 2
-bash-4.4$
This builtin returns necessary information to user space
to extract values from the bitfields.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D67980
Files:
clang/include/clang/Basic/Builtins.def
clang/lib/CodeGen/CGBuiltin.cpp
clang/lib/Sema/SemaChecking.cpp
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -1429,6 +1429,19 @@
if (SemaBuiltinPreserveAI(*this, TheCall))
return ExprError();
break;
+ case Builtin::BI__builtin_bitfield_info: {
+ if (checkArgCount(*this, TheCall, 1))
+ return ExprError();
+
+ Expr *Arg = TheCall->getArg(0);
+ if (Arg->getType()->getAsPlaceholderType())
+ return ExprError();
+ if (Arg->IgnoreParens()->getObjectKind() != OK_BitField)
+ return ExprError();
+
+ TheCall->setType(Context.UnsignedLongLongTy);
+ break;
+ }
case Builtin::BI__builtin_call_with_static_chain:
if (SemaBuiltinCallWithStaticChain(*this, TheCall))
return ExprError();
Index: clang/lib/CodeGen/CGBuiltin.cpp
===================================================================
--- clang/lib/CodeGen/CGBuiltin.cpp
+++ clang/lib/CodeGen/CGBuiltin.cpp
@@ -1882,6 +1882,13 @@
IsInPreservedAIRegion = false;
return RValue::get(Res);
}
+ case Builtin::BI__builtin_bitfield_info: {
+ const CGBitFieldInfo &Info = EmitLValue(E->getArg(0)).getBitFieldInfo();
+ uint64_t Val = ((Info.StorageOffset.getQuantity() * 8 + Info.Offset) <<
16) |
+ (Info.IsSigned << 15) |
+ Info.Size;
+ return RValue::get(ConstantInt::get(Int64Ty, Val));
+ }
case Builtin::BI__builtin_cimag:
case Builtin::BI__builtin_cimagf:
Index: clang/include/clang/Basic/Builtins.def
===================================================================
--- clang/include/clang/Basic/Builtins.def
+++ clang/include/clang/Basic/Builtins.def
@@ -1469,6 +1469,7 @@
BUILTIN(__builtin_char_memchr, "c*cC*iz", "n")
BUILTIN(__builtin_dump_struct, "ivC*v*", "tn")
BUILTIN(__builtin_preserve_access_index, "v.", "t")
+BUILTIN(__builtin_bitfield_info, "LLUi.", "t")
// Safestack builtins
BUILTIN(__builtin___get_unsafe_stack_start, "v*", "Fn")
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -1429,6 +1429,19 @@
if (SemaBuiltinPreserveAI(*this, TheCall))
return ExprError();
break;
+ case Builtin::BI__builtin_bitfield_info: {
+ if (checkArgCount(*this, TheCall, 1))
+ return ExprError();
+
+ Expr *Arg = TheCall->getArg(0);
+ if (Arg->getType()->getAsPlaceholderType())
+ return ExprError();
+ if (Arg->IgnoreParens()->getObjectKind() != OK_BitField)
+ return ExprError();
+
+ TheCall->setType(Context.UnsignedLongLongTy);
+ break;
+ }
case Builtin::BI__builtin_call_with_static_chain:
if (SemaBuiltinCallWithStaticChain(*this, TheCall))
return ExprError();
Index: clang/lib/CodeGen/CGBuiltin.cpp
===================================================================
--- clang/lib/CodeGen/CGBuiltin.cpp
+++ clang/lib/CodeGen/CGBuiltin.cpp
@@ -1882,6 +1882,13 @@
IsInPreservedAIRegion = false;
return RValue::get(Res);
}
+ case Builtin::BI__builtin_bitfield_info: {
+ const CGBitFieldInfo &Info = EmitLValue(E->getArg(0)).getBitFieldInfo();
+ uint64_t Val = ((Info.StorageOffset.getQuantity() * 8 + Info.Offset) << 16) |
+ (Info.IsSigned << 15) |
+ Info.Size;
+ return RValue::get(ConstantInt::get(Int64Ty, Val));
+ }
case Builtin::BI__builtin_cimag:
case Builtin::BI__builtin_cimagf:
Index: clang/include/clang/Basic/Builtins.def
===================================================================
--- clang/include/clang/Basic/Builtins.def
+++ clang/include/clang/Basic/Builtins.def
@@ -1469,6 +1469,7 @@
BUILTIN(__builtin_char_memchr, "c*cC*iz", "n")
BUILTIN(__builtin_dump_struct, "ivC*v*", "tn")
BUILTIN(__builtin_preserve_access_index, "v.", "t")
+BUILTIN(__builtin_bitfield_info, "LLUi.", "t")
// Safestack builtins
BUILTIN(__builtin___get_unsafe_stack_start, "v*", "Fn")
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