[FIRRTL] InferWidths: Don't need to duplicate InvalidValues

We used to duplicate InvalidValues to their uses, so that each use could
be inferred separately.  This was because InvalidValues were considered
constants, and things like CSE might combine many unknown-width invalid
values, and we wanted to counteract this affect.  InvalidValues are no
longer pure, and so will not be CSE'd away this way anymore, making this
code no longer needed.

lib/Dialect/FIRRTL/Transforms/InferWidths.cpp

@@ -1400,21 +1400,6 @@ LogicalResult InferenceMapping::mapOperation(Operation *op) {
         // We must duplicate the invalid value for each use, since each use can
         // be inferred to a different width.
         declareVars(op.getResult(), op.getLoc(), /*isDerived=*/true);
-        if (op.use_empty())
-          return;
-
-        auto type = op.getType();
-        ImplicitLocOpBuilder builder(op->getLoc(), op);
-        for (auto &use :
-             llvm::make_early_inc_range(llvm::drop_begin(op->getUses()))) {
-          // - `make_early_inc_range` since `getUses()` is invalidated upon
-          //   `use.set(...)`.
-          // - `drop_begin` such that the first use can keep the original op.
-          auto clone = builder.create<InvalidValueOp>(type);
-          declareVars(clone.getResult(), clone.getLoc(),
-                      /*isDerived=*/true);
-          use.set(clone);
-        }
       })
       .Case<WireOp, RegOp>(
           [&](auto op) { declareVars(op.getResult(), op.getLoc()); })

test/Dialect/FIRRTL/infer-widths.mlir

@@ -35,15 +35,6 @@ firrtl.circuit "Foo" {
     firrtl.connect %out, %invalid_ui : !firrtl.uint, !firrtl.uint
     firrtl.connect %out, %c42_ui : !firrtl.uint, !firrtl.uint
 
-    // Check that the invalid values are duplicated, and a corner case where the
-    // wire won't be updated with a width until after updating the invalid value
-    // above.
-    // CHECK: %invalid_ui2 = firrtl.invalidvalue : !firrtl.uint<2>
-    %w = firrtl.wire : !firrtl.uint
-    %c2_ui = firrtl.constant 2 : !firrtl.uint
-    firrtl.connect %w, %invalid_ui : !firrtl.uint, !firrtl.uint
-    firrtl.connect %w, %c2_ui : !firrtl.uint, !firrtl.uint
-
     // Check that invalid values are inferred to width zero if not used in a
     // connect.
     // CHECK: firrtl.invalidvalue : !firrtl.uint<0>