2 files changed, 88 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index a10d8e791b0..06192bd2eea 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -377,6 +377,10 @@ CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
     }
     return;
   }
+
+  llvm::Type *WordType =
+      DataLayout.getLargestLegalIntType(Types.getLLVMContext());
+  uint64_t WordSize = WordType ? DataLayout.getTypeSizeInBits(WordType) : 0;
   for (;;) {
     // Check to see if we need to start a new run.
     if (Run == FieldEnd) {
@@ -392,9 +396,12 @@ CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
       ++Field;
       continue;
     }
-    // Add bitfields to the run as long as they qualify.
+    // Add bitfields to the run as long as they qualify. If we end up on a word
+    // boundary we insert a break since it's equivalent and very wide types are
+    // harder to optimize with.
     if (Field != FieldEnd && Field->getBitWidthValue(Context) != 0 &&
-        Tail == getFieldBitOffset(*Field)) {
+        Tail == getFieldBitOffset(*Field) &&
+        WordSize != Tail - StartBitOffset) {
       Tail += Field->getBitWidthValue(Context);
       ++Field;
       continue;
diff --git a/clang/test/CodeGen/bitfield-machinewords.c b/clang/test/CodeGen/bitfield-machinewords.c
new file mode 100644
index 00000000000..3d370e7112f
--- /dev/null
+++ b/clang/test/CodeGen/bitfield-machinewords.c
@@ -0,0 +1,79 @@
+// RUN: %clang_cc1 -triple i386-unknown-unknown %s -emit-llvm -o - | FileCheck %s -check-prefix=CHECK32
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -emit-llvm -o - | FileCheck %s -check-prefix=CHECK64
+
+typedef unsigned long long uint64_t;
+
+struct thirty_two_bit_fields {
+  unsigned int ttbf1 : 32;
+  unsigned int ttbf2 : 32;
+  unsigned int ttbf3 : 32;
+  unsigned int ttbf4 : 32;
+};
+void ttbf(struct thirty_two_bit_fields *x) {}
+// CHECK32: %struct.thirty_two_bit_fields = type { i32, i32, i32, i32 }
+// CHECK64: %struct.thirty_two_bit_fields = type { i64, i64 }
+
+struct thirty_two_in_sixty_four {
+  uint64_t ttisf1 : 32;
+  uint64_t ttisf2 : 32;
+  uint64_t ttisf3 : 32;
+  uint64_t ttisf4 : 32;
+};
+void ttisf(struct thirty_two_in_sixty_four *x) {}
+// CHECK32: %struct.thirty_two_in_sixty_four = type { i32, i32, i32, i32 }
+// CHECK64: %struct.thirty_two_in_sixty_four = type { i64, i64 }
+
+struct everything_fits {
+  unsigned int ef1 : 2;
+  unsigned int ef2 : 29;
+  unsigned int ef3 : 1;
+
+  unsigned int ef4 : 16;
+  unsigned int ef5 : 16;
+
+  unsigned int ef6 : 7;
+  unsigned int ef7 : 25;
+};
+void ef(struct everything_fits *x) {}
+// CHECK32: %struct.everything_fits = type { i32, i32, i32 }
+// CHECK64: %struct.everything_fits = type <{ i64, i32 }>
+
+struct not_lined_up {
+  uint64_t nlu1 : 31;
+  uint64_t nlu2 : 2;
+  uint64_t nlu3 : 32;
+  uint64_t nlu4 : 31;
+};
+void nlu(struct not_lined_up *x) {}
+// CHECK32: %struct.not_lined_up = type { i96 }
+// CHECK64: %struct.not_lined_up = type { i40, i64 }
+
+struct padding_between_words {
+  unsigned int pbw1 : 16;
+  unsigned int pbw2 : 14;
+
+  unsigned int pbw3 : 12;
+  unsigned int pbw4 : 16;
+
+  unsigned int pbw5 : 8;
+  unsigned int pbw6 : 10;
+
+  unsigned int pbw7 : 20;
+  unsigned int pbw8 : 10;
+};
+void pbw(struct padding_between_words *x) {}
+// CHECK32: %struct.padding_between_words = type { i32, i32, i24, i32 }
+// CHECK64: %struct.padding_between_words = type { i32, i32, i24, i32 }
+
+struct unaligned_are_coalesced {
+  uint64_t uac1 : 16;
+  uint64_t uac2 : 32;
+  uint64_t uac3 : 16;
+  uint64_t uac4 : 48;
+  uint64_t uac5 : 64;
+  uint64_t uac6 : 16;
+  uint64_t uac7 : 32;
+};
+void uac(struct unaligned_are_coalesced *x) {}
+// CHECK32: %struct.unaligned_are_coalesced = type { i112, i112 }
+// CHECK64: %struct.unaligned_are_coalesced = type { i64, i48, i64, i48 }