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[LLHD] Support conditional drives in mem2reg #8278

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merged 1 commit into from
Feb 26, 2025
Merged

[LLHD] Support conditional drives in mem2reg #8278

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20 changes: 11 additions & 9 deletions lib/Dialect/LLHD/Transforms/Mem2Reg.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,11 +40,11 @@ static bool isEpsilonDelay(Value value) {
return false;
}

/// Check whether an operation is a `llhd.drive` with no enable condition and an
/// epsilon delay. This corresponds to a blocking assignment in Verilog.
static bool isUnconditionalBlockingDrive(Operation *op) {
/// Check whether an operation is a `llhd.drive` with an epsilon delay. This
/// corresponds to a blocking assignment in Verilog.
static bool isBlockingDrive(Operation *op) {
if (auto driveOp = dyn_cast<DrvOp>(op))
return !driveOp.getEnable() && isEpsilonDelay(driveOp.getTime());
return isEpsilonDelay(driveOp.getTime());
return false;
}

Expand Down Expand Up @@ -278,7 +278,7 @@ struct DriveNode : public OpNode {
LatticeValue *valueAfter)
: OpNode(Kind::Drive, op, valueBefore, valueAfter), slot(op.getSignal()),
value(op.getValue()), def(def) {
assert(isUnconditionalBlockingDrive(op));
assert(isBlockingDrive(op));
}

static bool classof(const LatticeNode *n) { return n->kind == Kind::Drive; }
Expand Down Expand Up @@ -608,7 +608,7 @@ void Promoter::findPromotableSlots() {
// Ignore uses outside of the region.
if (user->getParentRegion() != &region)
return true;
return isa<PrbOp>(user) || isUnconditionalBlockingDrive(user);
return isa<PrbOp>(user) || isBlockingDrive(user);
}))
continue;

Expand Down Expand Up @@ -765,12 +765,14 @@ void Promoter::constructLattice() {

// Handle drives.
if (auto driveOp = dyn_cast<DrvOp>(op)) {
if (!isUnconditionalBlockingDrive(&op))
if (!isBlockingDrive(&op))
continue;
if (!slotOrder.contains(driveOp.getSignal()))
continue;
auto *def =
lattice.createDef(driveOp.getValue(), DriveCondition::always());
auto condition = DriveCondition::always();
if (auto enable = driveOp.getEnable())
condition = DriveCondition::conditional(enable);
auto *def = lattice.createDef(driveOp.getValue(), condition);
auto *node = lattice.createNode<DriveNode>(driveOp, def, valueBefore,
lattice.createValue());
valueBefore = node->valueAfter;
Expand Down
53 changes: 53 additions & 0 deletions test/Dialect/LLHD/Transforms/mem2reg.mlir
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Original file line number Diff line number Diff line change
Expand Up @@ -440,5 +440,58 @@ hw.module @CaptureAcrossWaits(in %u: i42, in %bool: i1) {
}
}

// Conditional drive forwarding.
// CHECK-LABEL: @ConditionalDrives
hw.module @ConditionalDrives(in %u: i42, in %v: i42, in %q: i1, in %r: i1) {
%0 = llhd.constant_time <0ns, 0d, 1e>
%a = llhd.sig %u : i42
// CHECK: llhd.process
llhd.process {
// CHECK-NEXT: llhd.constant_time
// CHECK-NEXT: llhd.drv %a, %u after {{%.+}} if %q
llhd.drv %a, %u after %0 if %q : !hw.inout<i42>
// CHECK-NEXT: llhd.halt
llhd.halt
}
// CHECK: llhd.process
llhd.process {
// CHECK-NOT: llhd.drv
llhd.drv %a, %u after %0 if %q : !hw.inout<i42>
// CHECK-NEXT: cf.br ^bb2(%u : i42)
cf.br ^bb2
^bb1:
// CHECK-NEXT: ^bb1:
// CHECK-NOT: llhd.drv
llhd.drv %a, %v after %0 if %q : !hw.inout<i42>
// CHECK-NEXT: cf.br ^bb2(%v : i42)
cf.br ^bb2
^bb2:
// CHECK-NEXT: ^bb2([[A:%.+]]: i42):
// CHECK-NEXT: llhd.constant_time
// CHECK-NEXT: llhd.drv %a, [[A]] after {{%.+}} if %q
// CHECK-NEXT: llhd.halt
llhd.halt
}
// CHECK: llhd.process
llhd.process {
// CHECK-NOT: llhd.drv
llhd.drv %a, %u after %0 if %q : !hw.inout<i42>
// CHECK-NEXT: cf.br ^bb2(%u, %q : i42, i1)
cf.br ^bb2
^bb1:
// CHECK-NEXT: ^bb1:
// CHECK-NOT: llhd.drv
llhd.drv %a, %v after %0 if %r : !hw.inout<i42>
// CHECK-NEXT: cf.br ^bb2(%v, %r : i42, i1)
cf.br ^bb2
^bb2:
// CHECK-NEXT: ^bb2([[A:%.+]]: i42, [[ACOND:%.+]]: i1):
// CHECK-NEXT: llhd.constant_time
// CHECK-NEXT: llhd.drv %a, [[A]] after {{%.+}} if [[ACOND]]
// CHECK-NEXT: llhd.halt
llhd.halt
}
}

func.func private @use_i42(%arg0: i42)
func.func private @use_inout_i42(%arg0: !hw.inout<i42>)
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