Revert "[FIRRTL] Add folder for mul (#8222)"

This reverts commit a511fda.

In downstream testing, this folder appeared to cause assertions in
upstream MLIR to fail with the following:

```
llvm::APSInt mlir::IntegerAttr::getAPSInt() const: Assertion
`!getType().isSignlessInteger() && "Signless integers don't carry a
sign for APSInt"' failed.
```

Author: mikeurbach

include/circt/Dialect/FIRRTL/FIRRTLExpressions.td

@@ -1409,8 +1409,6 @@ def IntegerMulOp : IntegerBinaryPrimOp<"integer.mul", [Commutative]> {
                                          !firrtl.integer
     ```
   }];
-
-  let hasFolder = true;
 }
 
 def IntegerShrOp : IntegerBinaryPrimOp<"integer.shr"> {

lib/Dialect/FIRRTL/FIRRTLFolds.cpp

@@ -953,19 +953,8 @@ OpFoldResult IntegerAddOp::fold(FoldAdaptor adaptor) {
 }
 
 OpFoldResult IntegerMulOp::fold(FoldAdaptor adaptor) {
-  if (auto rhsCst = getConstant(adaptor.getRhs())) {
-    // Constant folding
-    if (auto lhsCst = getConstant(adaptor.getLhs())) {
-      auto resultWidth = lhsCst->getBitWidth() + rhsCst->getBitWidth();
-      APSInt lhsCstExt = (*lhsCst).extend(resultWidth);
-      APSInt rhsCstExt = (*rhsCst).extend(resultWidth);
-      return IntegerAttr::get(IntegerType::get(getContext(), resultWidth),
-                              lhsCstExt * rhsCstExt);
-    }
-    // x * 1 -> x
-    if (rhsCst->isOne())
-      return getLhs();
-  }
+  // TODO: implement constant folding, etc.
+  // Tracked in https://github.com/llvm/circt/issues/6724.
   return {};
 }
 

test/Dialect/FIRRTL/canonicalization.mlir

@@ -3576,14 +3576,12 @@ firrtl.module private @Issue7562(in %sel : !firrtl.uint<1>, in %a : !firrtl.cons
 }
 
 // CHECK-LABEL: firrtl.class @PropertyArithmetic
-firrtl.class @PropertyArithmetic(in %in: !firrtl.integer, out %out0: !firrtl.integer, out %out1: !firrtl.integer, out %out2: !firrtl.integer, out %out3: !firrtl.integer, out %out4: !firrtl.integer, out %out5: !firrtl.integer) {
-  // CHECK: [[C10000:%.+]] = firrtl.integer 10000
+firrtl.class @PropertyArithmetic(in %in: !firrtl.integer, out %out0: !firrtl.integer, out %out1: !firrtl.integer, out %out2: !firrtl.integer, out %out3: !firrtl.integer) {
   // CHECK: [[C3:%.+]] = firrtl.integer 3
   // CHECK: [[C4:%.+]] = firrtl.integer 4
   %0 = firrtl.integer 0
   %1 = firrtl.integer 1
   %2 = firrtl.integer 2
-  %100 = firrtl.integer 100
 
   %res0 = firrtl.integer.shl %1, %2 : (!firrtl.integer, !firrtl.integer) -> !firrtl.integer
   %res1 = firrtl.integer.shl %in, %0 : (!firrtl.integer, !firrtl.integer) -> !firrtl.integer
@@ -3600,14 +3598,6 @@ firrtl.class @PropertyArithmetic(in %in: !firrtl.integer, out %out0: !firrtl.int
   // CHECK: firrtl.propassign %out3, %in
   firrtl.propassign %out2, %res2 : !firrtl.integer
   firrtl.propassign %out3, %res3 : !firrtl.integer
-
-  %res4 = firrtl.integer.mul %100, %100 : (!firrtl.integer, !firrtl.integer) -> !firrtl.integer
-  %res5 = firrtl.integer.mul %in, %1 : (!firrtl.integer, !firrtl.integer) -> !firrtl.integer
-
-  // CHECK: firrtl.propassign %out4, [[C10000]]
-  // CHECK: firrtl.propassign %out5, %in
-  firrtl.propassign %out4, %res4 : !firrtl.integer
-  firrtl.propassign %out5, %res5 : !firrtl.integer
 }
 
 // CHECK-LABEL: firrtl.module private @LayerBlocks