spetrovic created this revision.
Herald added subscribers: arichardson, sdardis.
This patch provides that bitfields are splitted even in case when current field
is not legal integer type. For Example,
struct S3 {
unsigned long a1:28;
unsigned long a2:4;
unsigned long a3:12;
};
struct S4 {
unsigned long long b1:61;
unsigned long b2:3;
unsigned long b3:3;
};
At the moment, S3 is i48 type, and S4 is i72 type, with this change S3 is
treated as i32 + 16, and S4 is treated as i32 + i32 + i8.
With this patch we avoid unaligned loads and stores, at least on MIPS
architecture.
https://reviews.llvm.org/D39053
Files:
lib/CodeGen/CGRecordLayoutBuilder.cpp
test/CodeGenCXX/finegrain-bitfield-type.cpp
Index: test/CodeGenCXX/finegrain-bitfield-type.cpp
===================================================================
--- test/CodeGenCXX/finegrain-bitfield-type.cpp
+++ test/CodeGenCXX/finegrain-bitfield-type.cpp
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -ffine-grained-bitfield-accesses \
+// RUN: -emit-llvm -o - %s | FileCheck %s
+struct S4 {
+ unsigned long f1:28;
+ unsigned long f2:4;
+ unsigned long f3:12;
+};
+struct S4 a4;
+
+struct S5 {
+ unsigned long f1:28;
+ unsigned long f2:4;
+ unsigned long f3:28;
+ unsigned long f4:4;
+ unsigned long f5:12;
+};
+struct S5 a5;
+
+
+// CHECK: %struct.S4 = type { i32, i16 }
+// CHECK-NOT: %struct.S4 = type { i48 }
+// CHECK: %struct.S5 = type { i32, i32, i16, [6 x i8] }
+// CHECK-NOT: %struct.S5 = type { i80 }
\ No newline at end of file
Index: lib/CodeGen/CGRecordLayoutBuilder.cpp
===================================================================
--- lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -408,15 +408,15 @@
// has legal integer width, and its bitfield offset is naturally aligned, it
// is better to make the bitfield a separate storage component so as it can
be
// accessed directly with lower cost.
- auto IsBetterAsSingleFieldRun = [&](RecordDecl::field_iterator Field) {
+ auto IsBetterAsSingleFieldRun = [&](uint64_t OffsetInRecord,
+ uint64_t StartBitOffset) {
if (!Types.getCodeGenOpts().FineGrainedBitfieldAccesses)
return false;
- unsigned Width = Field->getBitWidthValue(Context);
- if (!DataLayout.isLegalInteger(Width))
+ if (!DataLayout.isLegalInteger(OffsetInRecord))
return false;
// Make sure Field is natually aligned if it is treated as an IType
integer.
- if (getFieldBitOffset(*Field) %
- Context.toBits(getAlignment(getIntNType(Width))) !=
+ if (StartBitOffset %
+ Context.toBits(getAlignment(getIntNType(OffsetInRecord))) !=
0)
return false;
return true;
@@ -435,7 +435,8 @@
Run = Field;
StartBitOffset = getFieldBitOffset(*Field);
Tail = StartBitOffset + Field->getBitWidthValue(Context);
- StartFieldAsSingleRun = IsBetterAsSingleFieldRun(Run);
+ StartFieldAsSingleRun = IsBetterAsSingleFieldRun(Tail - StartBitOffset,
+ StartBitOffset);
}
++Field;
continue;
@@ -449,7 +450,7 @@
// skip the block below and go ahead to emit the storage.
// Otherwise, try to add bitfields to the run.
if (!StartFieldAsSingleRun && Field != FieldEnd &&
- !IsBetterAsSingleFieldRun(Field) &&
+ !IsBetterAsSingleFieldRun(Tail - StartBitOffset, StartBitOffset) &&
Field->getBitWidthValue(Context) != 0 &&
Tail == getFieldBitOffset(*Field)) {
Tail += Field->getBitWidthValue(Context);
Index: test/CodeGenCXX/finegrain-bitfield-type.cpp
===================================================================
--- test/CodeGenCXX/finegrain-bitfield-type.cpp
+++ test/CodeGenCXX/finegrain-bitfield-type.cpp
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -ffine-grained-bitfield-accesses \
+// RUN: -emit-llvm -o - %s | FileCheck %s
+struct S4 {
+ unsigned long f1:28;
+ unsigned long f2:4;
+ unsigned long f3:12;
+};
+struct S4 a4;
+
+struct S5 {
+ unsigned long f1:28;
+ unsigned long f2:4;
+ unsigned long f3:28;
+ unsigned long f4:4;
+ unsigned long f5:12;
+};
+struct S5 a5;
+
+
+// CHECK: %struct.S4 = type { i32, i16 }
+// CHECK-NOT: %struct.S4 = type { i48 }
+// CHECK: %struct.S5 = type { i32, i32, i16, [6 x i8] }
+// CHECK-NOT: %struct.S5 = type { i80 }
\ No newline at end of file
Index: lib/CodeGen/CGRecordLayoutBuilder.cpp
===================================================================
--- lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -408,15 +408,15 @@
// has legal integer width, and its bitfield offset is naturally aligned, it
// is better to make the bitfield a separate storage component so as it can be
// accessed directly with lower cost.
- auto IsBetterAsSingleFieldRun = [&](RecordDecl::field_iterator Field) {
+ auto IsBetterAsSingleFieldRun = [&](uint64_t OffsetInRecord,
+ uint64_t StartBitOffset) {
if (!Types.getCodeGenOpts().FineGrainedBitfieldAccesses)
return false;
- unsigned Width = Field->getBitWidthValue(Context);
- if (!DataLayout.isLegalInteger(Width))
+ if (!DataLayout.isLegalInteger(OffsetInRecord))
return false;
// Make sure Field is natually aligned if it is treated as an IType integer.
- if (getFieldBitOffset(*Field) %
- Context.toBits(getAlignment(getIntNType(Width))) !=
+ if (StartBitOffset %
+ Context.toBits(getAlignment(getIntNType(OffsetInRecord))) !=
0)
return false;
return true;
@@ -435,7 +435,8 @@
Run = Field;
StartBitOffset = getFieldBitOffset(*Field);
Tail = StartBitOffset + Field->getBitWidthValue(Context);
- StartFieldAsSingleRun = IsBetterAsSingleFieldRun(Run);
+ StartFieldAsSingleRun = IsBetterAsSingleFieldRun(Tail - StartBitOffset,
+ StartBitOffset);
}
++Field;
continue;
@@ -449,7 +450,7 @@
// skip the block below and go ahead to emit the storage.
// Otherwise, try to add bitfields to the run.
if (!StartFieldAsSingleRun && Field != FieldEnd &&
- !IsBetterAsSingleFieldRun(Field) &&
+ !IsBetterAsSingleFieldRun(Tail - StartBitOffset, StartBitOffset) &&
Field->getBitWidthValue(Context) != 0 &&
Tail == getFieldBitOffset(*Field)) {
Tail += Field->getBitWidthValue(Context);
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