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[CIR][NFC] Add example for get_bitfield with volatile qualifier (#147828)

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The example demonstrates how `get_bitfield` is emitted when accessing a
bitfield declared as `volatile`.
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Andres-Salamanca 2025-07-10 18:05:58 -05:00 committed by GitHub
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3
clang/include/clang/CIR/Dialect/IR/CIROps.td
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@ -1773,6 +1773,9 @@ def GetBitfieldOp : CIR_Op<"get_bitfield"> {
A unit attribute `volatile` can be used to indicate a volatile load of the
bitfield.
```mlir
cir.get_bitfield(#bfi, %0 {is_volatile} : !cir.ptr<!u64i>) -> !s32i
```
Example:
Suppose we have a struct with multiple bitfields stored in

28
clang/test/CIR/CodeGen/bitfields.c
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@ -213,6 +213,34 @@ typedef struct {
int c;
} V;
void get_volatile(V* v) {
v->b = 3;
}
// CIR: cir.func dso_local @get_volatile
// CIR: [[TMP0:%.*]] = cir.alloca !cir.ptr<!rec_V>, !cir.ptr<!cir.ptr<!rec_V>>, ["v", init] {alignment = 8 : i64}
// CIR: [[TMP1:%.*]] = cir.const #cir.int<3> : !s32i
// CIR: [[TMP2:%.*]] = cir.load align(8) [[TMP0]] : !cir.ptr<!cir.ptr<!rec_V>>, !cir.ptr<!rec_V>
// CIR: [[TMP3:%.*]] = cir.get_member [[TMP2]][0] {name = "b"} : !cir.ptr<!rec_V> -> !cir.ptr<!u64i>
// CIR: [[TMP4:%.*]] = cir.set_bitfield(#bfi_b, [[TMP3]] : !cir.ptr<!u64i>, [[TMP1]] : !s32i) {is_volatile} -> !s32i
// LLVM: define dso_local void @get_volatile
// LLVM: [[TMP0:%.*]] = alloca ptr, i64 1, align 8
// LLVM: [[TMP1:%.*]] = load ptr, ptr [[TMP0]], align 8
// LLVM: [[TMP2:%.*]] = getelementptr %struct.V, ptr [[TMP1]], i32 0, i32 0
// LLVM: [[TMP3:%.*]] = load volatile i64, ptr [[TMP2]], align 8
// LLVM: [[TMP4:%.*]] = and i64 [[TMP3]], -1095216660481
// LLVM: [[TMP5:%.*]] = or i64 [[TMP4]], 12884901888
// LLVM: store volatile i64 [[TMP5]], ptr [[TMP2]], align 8
// OCGC: define dso_local void @get_volatile
// OCGC: [[TMP0:%.*]] = alloca ptr, align 8
// OCGC: [[TMP1:%.*]] = load ptr, ptr [[TMP0]], align 8
// OCGC: [[TMP2:%.*]] = load volatile i64, ptr [[TMP1]], align 4
// OCGC: [[TMP3:%.*]] = and i64 [[TMP2]], -1095216660481
// OCGC: [[TMP4:%.*]] = or i64 [[TMP3]], 12884901888
// OCGC: store volatile i64 [[TMP4]], ptr [[TMP1]], align 4
void set_volatile(V* v) {
v->b = 3;
}