[CodeGen] Fix an assertion failure in CGRecordLowering.

This patch fixes a bug in CGRecordLowering::accumulateBitFields where it
unconditionally starts a new run and emits a storage field when it sees
a zero-sized bitfield, which causes an assertion in insertPadding to
fail when -fno-bitfield-type-align is used.

It shouldn't emit new storage if UseZeroLengthBitfieldAlignment and
UseBitFieldTypeAlignment are both false.

rdar://problem/36762205

llvm-svn: 323943

2 files changed, 50 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index 1644ab4c072..d794b12b3d3 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -443,14 +443,18 @@ CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
 
     // If the start field of a new run is better as a single run, or
     // if current field is better as a single run, or
-    // if current field has zero width bitfield, or
+    // if current field has zero width bitfield and either
+    // UseZeroLengthBitfieldAlignment or UseBitFieldTypeAlignment is set to
+    // true, or
     // if the offset of current field is inconsistent with the offset of
     // previous field plus its offset,
     // 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) &&
-        Field->getBitWidthValue(Context) != 0 &&
+        (Field->getBitWidthValue(Context) != 0 ||
+         (!Context.getTargetInfo().useZeroLengthBitfieldAlignment() &&
+          !Context.getTargetInfo().useBitFieldTypeAlignment())) &&
         Tail == getFieldBitOffset(*Field)) {
       Tail += Field->getBitWidthValue(Context);
       ++Field;
diff --git a/clang/test/CodeGen/no-bitfield-type-align.c b/clang/test/CodeGen/no-bitfield-type-align.c
new file mode 100644
index 00000000000..830cd585c6b
--- /dev/null
+++ b/clang/test/CodeGen/no-bitfield-type-align.c
@@ -0,0 +1,44 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -fno-bitfield-type-align -emit-llvm -o - %s | FileCheck %s
+
+// CHECK: %[[STRUCT_S:.*]] = type { i32 }
+
+struct S {
+  unsigned short:   0;
+  unsigned short  f1:15;
+  unsigned short:   0;
+  unsigned short  f2:15;
+};
+
+// CHECK: define void @test_zero_width_bitfield(%[[STRUCT_S]]* %[[A:.*]])
+// CHECK: %[[BF_LOAD:.*]] = load i32, i32* %[[V1:.*]], align 1
+// CHECK: %[[BF_CLEAR:.*]] = and i32 %[[BF_LOAD]], 32767
+// CHECK: %[[BF_CAST:.*]] = trunc i32 %[[BF_CLEAR]] to i16
+// CHECK: %[[CONV:.*]] = zext i16 %[[BF_CAST]] to i32
+// CHECK: %[[ADD:.*]] = add nsw i32 %[[CONV]], 1
+// CHECK: %[[CONV1:.*]] = trunc i32 %[[ADD]] to i16
+// CHECK: %[[V2:.*]] = zext i16 %[[CONV1]] to i32
+// CHECK: %[[BF_LOAD2:.*]] = load i32, i32* %[[V1]], align 1
+// CHECK: %[[BF_VALUE:.*]] = and i32 %[[V2]], 32767
+// CHECK: %[[BF_CLEAR3:.*]] = and i32 %[[BF_LOAD2]], -32768
+// CHECK: %[[BF_SET:.*]] = or i32 %[[BF_CLEAR3]], %[[BF_VALUE]]
+// CHECK: store i32 %[[BF_SET]], i32* %[[V1]], align 1
+
+// CHECK: %[[BF_LOAD4:.*]] = load i32, i32* %[[V4:.*]], align 1
+// CHECK: %[[BF_LSHR:.*]] = lshr i32 %[[BF_LOAD4]], 15
+// CHECK: %[[BF_CLEAR5:.*]] = and i32 %[[BF_LSHR]], 32767
+// CHECK: %[[BF_CAST6:.*]] = trunc i32 %[[BF_CLEAR5]] to i16
+// CHECK: %[[CONV7:.*]] = zext i16 %[[BF_CAST6]] to i32
+// CHECK: %[[ADD8:.*]] = add nsw i32 %[[CONV7]], 2
+// CHECK: %[[CONV9:.*]] = trunc i32 %[[ADD8]] to i16
+// CHECK: %[[V5:.*]] = zext i16 %[[CONV9]] to i32
+// CHECK: %[[BF_LOAD10:.*]] = load i32, i32* %[[V4]], align 1
+// CHECK: %[[BF_VALUE11:.*]] = and i32 %[[V5]], 32767
+// CHECK: %[[BF_SHL:.*]] = shl i32 %[[BF_VALUE11]], 15
+// CHECK: %[[BF_CLEAR12:.*]] = and i32 %[[BF_LOAD10]], -1073709057
+// CHECK: %[[BF_SET13:.*]] = or i32 %[[BF_CLEAR12]], %[[BF_SHL]]
+// CHECK: store i32 %[[BF_SET13]], i32* %[[V4]], align 1
+
+void test_zero_width_bitfield(struct S *a) {
+  a->f1 += 1;
+  a->f2 += 2;
+}