[LLHD] Add Sig2Reg pass for graph regions

include/circt/Dialect/LLHD/Transforms/Passes.h

@@ -36,6 +36,7 @@ std::unique_ptr<OperationPass<hw::HWModuleOp>> createEarlyCodeMotionPass();
 
 std::unique_ptr<OperationPass<hw::HWModuleOp>> createTemporalCodeMotionPass();
 
+#define GEN_PASS_DECL_SIG2REG
 #define GEN_PASS_DECL_DESEQUENTIALIZATION
 #define GEN_PASS_REGISTRATION
 #include "circt/Dialect/LLHD/Transforms/Passes.h.inc"

include/circt/Dialect/LLHD/Transforms/Passes.td

@@ -111,6 +111,10 @@ def EarlyCodeMotion : Pass<"llhd-early-code-motion", "hw::HWModuleOp"> {
   let constructor = "circt::llhd::createEarlyCodeMotionPass()";
 }
 
+def Sig2Reg : Pass<"llhd-sig2reg", "hw::HWModuleOp"> {
+  let summary = "promote LLHD signals to SSA values";
+}
+
 def TemporalCodeMotion : Pass<"llhd-temporal-code-motion", "hw::HWModuleOp"> {
   let summary = "move drive operations to the exit basic block in processes";
   let description = [{

lib/Dialect/LLHD/Transforms/CMakeLists.txt

@@ -4,6 +4,7 @@ add_circt_dialect_library(CIRCTLLHDTransforms
   FunctionEliminationPass.cpp
   MemoryToBlockArgumentPass.cpp
   ProcessLoweringPass.cpp
+  Sig2RegPass.cpp
   TemporalCodeMotionPass.cpp
   TemporalRegions.cpp
 

lib/Dialect/LLHD/Transforms/Sig2RegPass.cpp

@@ -0,0 +1,114 @@
+//===- Sig2RegPass.cpp - Implement the Sig2Reg Pass -----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Implement Pass to promote LLHD signals to SSA values.
+//
+//===----------------------------------------------------------------------===//
+
+#include "circt/Dialect/HW/HWOps.h"
+#include "circt/Dialect/LLHD/IR/LLHDOps.h"
+#include "circt/Dialect/LLHD/Transforms/Passes.h"
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "llhd-sig2reg"
+
+namespace circt {
+namespace llhd {
+#define GEN_PASS_DEF_SIG2REG
+#include "circt/Dialect/LLHD/Transforms/Passes.h.inc"
+} // namespace llhd
+} // namespace circt
+
+using namespace mlir;
+using namespace circt;
+
+namespace {
+struct Sig2RegPass : public circt::llhd::impl::Sig2RegBase<Sig2RegPass> {
+  void runOnOperation() override;
+};
+} // namespace
+
+static LogicalResult promote(llhd::SignalOp sigOp) {
+  SmallVector<llhd::PrbOp> probes;
+  llhd::DrvOp driveOp;
+  for (auto *user : sigOp.getResult().getUsers()) {
+    if (user->getBlock() != sigOp->getBlock()) {
+      LLVM_DEBUG(
+          { llvm::dbgs() << "Promotion failed: user in other block\n"; });
+      return failure();
+    }
+
+    if (auto prbOp = dyn_cast<llhd::PrbOp>(user)) {
+      probes.push_back(prbOp);
+      continue;
+    }
+
+    if (auto drvOp = dyn_cast<llhd::DrvOp>(user)) {
+      if (driveOp) {
+        LLVM_DEBUG({ llvm::dbgs() << "Promotion failed: multiple drivers\n"; });
+        return failure();
+      }
+
+      if (drvOp.getEnable()) {
+        LLVM_DEBUG(
+            { llvm::dbgs() << "Promotion failed: conditional driver\n"; });
+        return failure();
+      }
+
+      driveOp = drvOp;
+      continue;
+    }
+
+    LLVM_DEBUG({
+      llvm::dbgs() << "Promotion failed: user that is not a probe or drive: "
+                   << *user << "\n";
+    });
+    return failure();
+  }
+
+  Value replacement;
+  if (driveOp) {
+    auto timeOp = driveOp.getTime().getDefiningOp<llhd::ConstantTimeOp>();
+    if (!timeOp)
+      return failure();
+
+    OpBuilder builder(driveOp);
+    if (timeOp.getValue().getTime() == 0 && timeOp.getValue().getDelta() == 0)
+      replacement = driveOp.getValue();
+    else
+      replacement = builder.create<llhd::DelayOp>(
+          driveOp.getLoc(), driveOp.getValue(), timeOp.getValue());
+  } else {
+    replacement = sigOp.getInit();
+  }
+
+  for (auto prb : probes) {
+    prb.getResult().replaceAllUsesWith(replacement);
+    prb.erase();
+  }
+
+  if (driveOp)
+    driveOp.erase();
+
+  return success();
+}
+
+void Sig2RegPass::runOnOperation() {
+  hw::HWModuleOp moduleOp = getOperation();
+
+  for (auto sigOp :
+       llvm::make_early_inc_range(moduleOp.getOps<llhd::SignalOp>())) {
+    LLVM_DEBUG(
+        { llvm::dbgs() << "\nAttempting to promote " << sigOp << "\n"; });
+    if (failed(promote(sigOp)))
+      continue;
+
+    LLVM_DEBUG({ llvm::dbgs() << "Successfully promoted!\n"; });
+    sigOp.erase();
+  }
+}

test/Dialect/LLHD/Transforms/sig2reg.mlir

@@ -0,0 +1,57 @@
+// RUN: circt-opt --llhd-sig2reg %s | FileCheck %s
+
+func.func @getTime() -> !llhd.time {
+  %time = llhd.constant_time <1ns, 0d, 0e>
+  return %time : !llhd.time
+}
+
+hw.module @basic(in %init : i32, in %cond : i1, in %in0 : i32, in %in1 : i32, out prb1 : i32, out prb2 : i32, out prb3 : i32, out prb4 : i32, out prb5 : i32, out prb6 : i32, out prb7 : i32) {
+  %opaque_time = func.call @getTime() : () -> !llhd.time
+  %epsilon = llhd.constant_time <0ns, 0d, 1e>
+  %delta = llhd.constant_time <0ns, 1d, 0e>
+
+  // Promoted without delay op
+  %sig1 = llhd.sig %init : i32
+  // Promoted with delay op
+  %sig2 = llhd.sig %init : i32
+  // Not promoted because time is opaque, can support if the delay op takes a
+  // time value instead of attribute
+  %sig3 = llhd.sig %init : i32
+  // Promoted to %init because no drive present
+  %sig4 = llhd.sig %init : i32
+  // Not promoted because of drive condition
+  %sig5 = llhd.sig %init : i32
+  // Not promoted because a user is in a nested region
+  %sig6 = llhd.sig %init : i32
+  // Not promoted because of multiple drivers
+  %sig7 = llhd.sig %init : i32
+
+  llhd.drv %sig1, %in0 after %epsilon : !hw.inout<i32>
+  // CHECK: [[DELAY:%.+]] = llhd.delay %in0 by <0ns, 1d, 0e> : i32
+  llhd.drv %sig2, %in0 after %delta : !hw.inout<i32>
+  llhd.drv %sig3, %in0 after %opaque_time : !hw.inout<i32>
+
+  llhd.drv %sig5, %in0 after %epsilon if %cond : !hw.inout<i32>
+
+  scf.if %cond {
+    llhd.drv %sig6, %in0 after %epsilon : !hw.inout<i32>
+  }
+
+  llhd.drv %sig7, %in0 after %epsilon : !hw.inout<i32>
+  llhd.drv %sig7, %in1 after %delta : !hw.inout<i32>
+
+  %prb1 = llhd.prb %sig1 : !hw.inout<i32>
+  %prb2 = llhd.prb %sig2 : !hw.inout<i32>
+  // CHECK: [[PRB3:%.+]] = llhd.prb %sig3
+  %prb3 = llhd.prb %sig3 : !hw.inout<i32>
+  %prb4 = llhd.prb %sig4 : !hw.inout<i32>
+  // CHECK: [[PRB5:%.+]] = llhd.prb %sig5
+  %prb5 = llhd.prb %sig5 : !hw.inout<i32>
+  // CHECK: [[PRB6:%.+]] = llhd.prb %sig6
+  %prb6 = llhd.prb %sig6 : !hw.inout<i32>
+  // CHECK: [[PRB7:%.+]] = llhd.prb %sig7
+  %prb7 = llhd.prb %sig7 : !hw.inout<i32>
+
+  // CHECK: hw.output %in0, [[DELAY]], [[PRB3]], %init, [[PRB5]], [[PRB6]], [[PRB7]] :
+  hw.output %prb1, %prb2, %prb3, %prb4, %prb5, %prb6, %prb7 : i32, i32, i32, i32, i32, i32, i32
+}