[clang] [CIR] Add initial support for bitfields in structs (PR #142041)

[Andy Kaylor via cfe-commits]

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@@ -0,0 +1,79 @@
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s --check-prefix=LLVM
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s --check-prefix=OGCG
+
+struct A {
+  char a, b, c;
+  unsigned bits : 3;
+  unsigned more_bits : 4;
+  unsigned still_more_bits : 7;
+};
+
+typedef struct {
+  int a : 4;
+  int b : 5;
+  int c;
+} D;
+
+typedef struct {
+  int a : 4;
+  int b : 27;
+  int c : 17;
+  int d : 2;
+  int e : 15;
+  unsigned f; // type other than int above, not a bitfield
+} S;
+
+typedef struct {
+  int a : 3;  // one bitfield with size < 8
+  unsigned b;
+} T;
+
+typedef struct {
+    char a;
+    char b;
+    char c;
+
+    // startOffset 24 bits, new storage from here
+    int d: 2;
+    int e: 2;
+    int f: 4;
+    int g: 25;
+    int h: 3;
+    int i: 4;
+    int j: 3;
+    int k: 8;
+
+    int l: 14; // need to be a part of the new storage
+               // because (tail - startOffset) is 65 after 'l' field
+} U;
+
+// CIR-DAG:  !rec_D = !cir.record<struct "D" {!u16i, !s32i}>
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andykaylor wrote:

It would be helpful to move the checks for each type to just below the source declaration.

https://github.com/llvm/llvm-project/pull/142041