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Reject adding truncations for connections on inferwidths #10100

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Reject adding truncations for connections on inferwidths #10100

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21 changes: 8 additions & 13 deletions lib/Dialect/FIRRTL/Transforms/InferWidths.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2081,9 +2081,9 @@ FailureOr<bool> InferenceTypeUpdate::updateOperation(Operation *op) {
anyChanged |= *result;
}

// If this is a connect operation, width inference might have inferred a RHS
// that is wider than the LHS, in which case an additional BitsPrimOp is
// necessary to truncate the value.
// If this is a connect operation, check that width inference did not infer a
// RHS that is wider than the LHS. Such a situation would require an
// implicit truncation, which is not allowed.
if (auto con = dyn_cast<ConnectOp>(op)) {
auto lhs = con.getDest();
auto rhs = con.getSrc();
Expand All @@ -2097,17 +2097,12 @@ FailureOr<bool> InferenceTypeUpdate::updateOperation(Operation *op) {
auto lhsWidth = lhsType.getBitWidthOrSentinel();
auto rhsWidth = rhsType.getBitWidthOrSentinel();
if (lhsWidth >= 0 && rhsWidth >= 0 && lhsWidth < rhsWidth) {
OpBuilder builder(op);
auto trunc = builder.createOrFold<TailPrimOp>(con.getLoc(), con.getSrc(),
rhsWidth - lhsWidth);
if (type_isa<SIntType>(rhsType))
trunc =
builder.createOrFold<AsSIntPrimOp>(con.getLoc(), lhsType, trunc);

LLVM_DEBUG(llvm::dbgs()
<< "Truncating RHS to " << lhsType << " in " << con << "\n");
con->replaceUsesOfWith(con.getSrc(), trunc);
con.emitError("connect would require truncation after width inference: "
"destination ")
<< lhsType << " is not as wide as the source " << rhsType;
return failure();
}

return anyChanged;
}

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15 changes: 15 additions & 0 deletions test/Dialect/FIRRTL/infer-widths-errors.mlir
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Original file line number Diff line number Diff line change
Expand Up @@ -182,3 +182,18 @@ firrtl.circuit "MuxSelTooWide" {
firrtl.connect %0, %c2_ui2 : !firrtl.uint, !firrtl.uint<2>
}
}

// -----

// Connections that would require truncation after width inference should
// produce a dedicated error rather than implicitly inserting truncation.
firrtl.circuit "TruncateConnect" {
firrtl.module @TruncateConnect() {
%w = firrtl.wire : !firrtl.uint
%c1_ui1 = firrtl.constant 1 : !firrtl.uint<1>
firrtl.connect %w, %c1_ui1 : !firrtl.uint, !firrtl.uint<1>
%w1 = firrtl.wire : !firrtl.uint<0>
// expected-error @+1 {{connect would require truncation after width inference: destination '!firrtl.uint<0>' is not as wide as the source '!firrtl.uint<1>'}}
firrtl.connect %w1, %w : !firrtl.uint<0>, !firrtl.uint
}
}
7 changes: 5 additions & 2 deletions test/Dialect/FIRRTL/infer-widths.mlir
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Expand Up @@ -479,8 +479,10 @@ firrtl.circuit "Foo" {
// CHECK: firrtl.connect %x, %c200_si9 : !firrtl.sint<9>
%x = firrtl.wire : !firrtl.sint
%c200_si = firrtl.constant 200 : !firrtl.sint
firrtl.connect %y, %x : !firrtl.sint<4>, !firrtl.sint
firrtl.connect %x, %c200_si : !firrtl.sint, !firrtl.sint
%0 = firrtl.tail %x, 5 : (!firrtl.sint) -> !firrtl.uint
%1 = firrtl.asSInt %0 : (!firrtl.uint) -> !firrtl.sint
firrtl.connect %y, %1 : !firrtl.sint<4>, !firrtl.sint
}

// Should truncate all the way to 0 bits if its has to.
Expand All @@ -492,7 +494,8 @@ firrtl.circuit "Foo" {
%w1 = firrtl.wire : !firrtl.uint<0>
// CHECK: %0 = firrtl.tail %w, 1 : (!firrtl.uint<1>) -> !firrtl.uint<0>
// CHECK: firrtl.connect %w1, %0 : !firrtl.uint<0>
firrtl.connect %w1, %w : !firrtl.uint<0>, !firrtl.uint
%0 = firrtl.tail %w, 1 : (!firrtl.uint) -> !firrtl.uint
firrtl.connect %w1, %0 : !firrtl.uint<0>, !firrtl.uint
}

// Issue #1110: Width inference should infer 0 width when appropriate
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