[FIRRTL] LowerToHW: guard against folded operations (#7358) (#7590)

In LowerToHW we copy the name from FIRRTL ops to the lowered HW ops. We often call `createOrFold` when creating the HW ops, which can mean that there is no operation to copy the name to. We were not properly detecting this scenario, which could cause us to try to copy the name to a null operation. Most ops were already covered under a guard in a generic code path, but div-like and subaccess-like operations needed to be guarded. Some of these problems are impossible to test right now as we require folders to be implemented for some operations. This backports #7358 to 1.62.0 for Chisel 6 users. Co-authored-by: Andrew Young <[email protected]>
llvm · Sep 6, 2024 · ba60dce · ba60dce
1 parent ccdef17
commit ba60dce
Show file tree

Hide file tree

Showing 2 changed files with 13 additions and 5 deletions.
diff --git a/lib/Conversion/FIRRTLToHW/LowerToHW.cpp b/lib/Conversion/FIRRTLToHW/LowerToHW.cpp
@@ -2604,7 +2604,8 @@ FailureOr<Value> FIRRTLLowering::lowerSubindex(SubindexOp op, Value input) {
     result = builder.createOrFold<sv::ArrayIndexInOutOp>(input, iIdx);
   else
     result = builder.createOrFold<hw::ArrayGetOp>(input, iIdx);
-  tryCopyName(result.getDefiningOp(), op);
+  if (auto *definingOp = result.getDefiningOp())
+    tryCopyName(definingOp, op);
   return result;
 }
 
@@ -2627,7 +2628,8 @@ FailureOr<Value> FIRRTLLowering::lowerSubaccess(SubaccessOp op, Value input) {
     result = builder.createOrFold<sv::ArrayIndexInOutOp>(input, valueIdx);
   else
     result = createArrayIndexing(input, valueIdx);
-  tryCopyName(result.getDefiningOp(), op);
+  if (auto *definingOp = result.getDefiningOp())
+    tryCopyName(definingOp, op);
   return result;
 }
 
@@ -2647,7 +2649,8 @@ FailureOr<Value> FIRRTLLowering::lowerSubfield(SubfieldOp op, Value input) {
     result = builder.createOrFold<sv::StructFieldInOutOp>(input, field);
   else
     result = builder.createOrFold<hw::StructExtractOp>(input, field);
-  tryCopyName(result.getDefiningOp(), op);
+  if (auto *definingOp = result.getDefiningOp())
+    tryCopyName(definingOp, op);
   return result;
 }
 
@@ -3500,7 +3503,8 @@ LogicalResult FIRRTLLowering::lowerDivLikeOp(Operation *op) {
   else
     result = builder.createOrFold<UnsignedOp>(lhs, rhs, true);
 
-  tryCopyName(result.getDefiningOp(), op);
+  if (auto *definingOp = result.getDefiningOp())
+    tryCopyName(definingOp, op);
 
   if (resultType == opType)
     return setLowering(op->getResult(0), result);

diff --git a/test/Conversion/FIRRTLToHW/lower-to-hw.mlir b/test/Conversion/FIRRTLToHW/lower-to-hw.mlir
@@ -239,7 +239,11 @@ firrtl.circuit "Simple"   attributes {annotations = [{class =
     // CHECK-NEXT: = comb.extract [[SHIFT]] from 0 : (i14) -> i4
     %31 = firrtl.dshr %25, %18 : (!firrtl.sint<4>, !firrtl.uint<14>) -> !firrtl.sint<4>
 
-    // CHECK-NEXT: comb.icmp bin ule {{.*}}, {{.*}} : i4
+    // Noop.
+    %c0_ui1 = firrtl.constant 0 : !firrtl.const.uint<1>
+    %32 = firrtl.dshr %in1, %c0_ui1 { name = "test" } : (!firrtl.uint<4>, !firrtl.const.uint<1>) -> !firrtl.uint<4>
+
+    // CHECK: comb.icmp bin ule {{.*}}, {{.*}} : i4
     %41 = firrtl.leq %in1, %4 : (!firrtl.uint<4>, !firrtl.uint<4>) -> !firrtl.uint<1>
     // CHECK-NEXT: comb.icmp bin ult {{.*}}, {{.*}} : i4
     %42 = firrtl.lt %in1, %4 : (!firrtl.uint<4>, !firrtl.uint<4>) -> !firrtl.uint<1>