[ExportVerilog] Add support for UnionCreate op. #5081
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This adds support for `hw::UnionCreateOp` to ExportVerilog. It works by
emitting a bit concatenation and assigning it to a wire with a union
type. Each union member may have a prepadding, which is decided by the
member's offset size, and a postpadding to ensure that each union
element is the same size. The resulting bitconcat is `{prepadding, data,
postpadding}`. If there is no padding for a particular member, then
bitconcat will not be used.
The following example has no offsets, but the member `a` requires
post-padding of `1` bit.
```mlir
hw.module @unionCreate(%in: i1) -> (out: !hw.union<a: i1, b: i2>) {
%0 = hw.union_create "a", %in : !hw.union<a: i1, b: i2>
hw.output %0 : !hw.union<a: i1, b: i2>
}
```
```verilog
module unionCreate(
input in,
output union packed { struct packed {logic a; logic [0:0] __post_padding_a;} a;logic [1:0] b;} out
);
assign out = {in, 1'h0};
endmodule
```
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youngar
commented
Apr 25, 2023
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| // If the element has no padding, emit it directly. | ||
| if (elementWidth == unionWidth) { | ||
| emitSubExpr(op.getInput(), Selection); |
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@uenoku I'm not sure if this is the correct precedence here.
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UnionCreate seems to be spilled to a wire so there is no correctness issue but I think LowestPrecedence is better. There is an extra parentheses for the following example:
hw.module @unionCreate(%in: i2) -> (out: !hw.union<a: i2, b: i2>) {
%add = comb.add %in, %in : i2
%0 = hw.union_create "a", %add : !hw.union<a: i2, b: i2>
hw.output %0 : !hw.union<a: i2, b: i2>
}
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Fixed here: #5091
Thanks Hideto!
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Sorry about the noise -- was looking at an old rev. |
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Thanks for taking a look @teqdruid, I would be grateful for any post-merge suggestions |
teqdruid
reviewed
Apr 25, 2023
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This adds support for
hw::UnionCreateOpto ExportVerilog. It works by emitting a bit concatenation and assigning it to a wire with a union type. Each union member may have a prepadding, which is decided by the member's offset size, and a postpadding to ensure that each union element is the same size. The resulting bitconcat is{prepadding, data, postpadding}. If there is no padding for a particular member, then bitconcat will not be used.The following example has no offsets, but the member
arequires post-padding of1bit.