[FIRRTL] Use PRINTF_FD macro instead of 0x80000002 as printf fd

updates the FIRRTLToHW conversion to use the `PRINTF_FD` macro for
specifying the file descriptor, allowing the fd to be obtained
externally. This change enhances flexibility by enabling the file
descriptor to be defined outside the conversion logic.

Signed-off-by: Clo91eaf <[email protected]>

lib/Conversion/FIRRTLToHW/LowerToHW.cpp

@@ -209,7 +209,7 @@ struct FIRRTLModuleLowering;
 /// This is state shared across the parallel module lowering logic.
 struct CircuitLoweringState {
   // Flags indicating whether the circuit uses certain header fragments.
-  std::atomic<bool> usedPrintfCond{false};
+  std::atomic<bool> usedPrintf{false};
   std::atomic<bool> usedAssertVerboseCond{false};
   std::atomic<bool> usedStopCond{false};
 
@@ -809,7 +809,19 @@ void FIRRTLModuleLowering::lowerFileHeader(CircuitOp op,
         guard, []() {}, body);
   };
 
-  if (state.usedPrintfCond) {
+  if (state.usedPrintf) {
+    b.create<sv::MacroDeclOp>("PRINTF_FD");
+    b.create<sv::MacroDeclOp>("PRINTF_FD_");
+    b.create<emit::FragmentOp>("PRINTF_FD_FRAGMENT", [&] {
+      b.create<sv::VerbatimOp>(
+          "\n// Users can define 'PRINTF_FD' to add a specified fd to "
+          "prints.");
+      emitGuard("PRINTF_FD_", [&]() {
+        emitGuardedDefine("PRINTF_FD", "PRINTF_FD_", "(`PRINTF_FD)",
+                          "32'h80000002");
+      });
+    });
+
     b.create<sv::MacroDeclOp>("PRINTF_COND");
     b.create<sv::MacroDeclOp>("PRINTF_COND_");
     b.create<emit::FragmentOp>("PRINTF_COND_FRAGMENT", [&] {
@@ -4416,7 +4428,8 @@ LogicalResult FIRRTLLowering::visitStmt(PrintFOp op) {
   circuitState.addMacroDecl(builder.getStringAttr("SYNTHESIS"));
   addToIfDefBlock("SYNTHESIS", std::function<void()>(), [&]() {
     addToAlwaysBlock(clock, [&]() {
-      circuitState.usedPrintfCond = true;
+      circuitState.usedPrintf = true;
+      circuitState.addFragment(theModule, "PRINTF_FD_FRAGMENT");
       circuitState.addFragment(theModule, "PRINTF_COND_FRAGMENT");
 
       // Emit an "sv.if '`PRINTF_COND_ & cond' into the #ifndef.
@@ -4425,9 +4438,10 @@ LogicalResult FIRRTLLowering::visitStmt(PrintFOp op) {
       ifCond = builder.createOrFold<comb::AndOp>(ifCond, cond, true);
 
       addIfProceduralBlock(ifCond, [&]() {
-        // Emit the sv.fwrite, writing to stderr by default.
-        Value fdStderr = builder.create<hw::ConstantOp>(APInt(32, 0x80000002));
-        builder.create<sv::FWriteOp>(fdStderr, op.getFormatString(), operands);
+        // Emit the sv.fwrite, writing to fd specified by `PRINTF_FD.
+        Value fd =
+            builder.create<sv::MacroRefExprOp>(cond.getType(), "PRINTF_FD_");
+        builder.create<sv::FWriteOp>(fd, op.getFormatString(), operands);
       });
     });
   });