[PATCH] D70066: [MacroFusion] Limit the max fused number as 2 to reduce the dependency

[qshanz via Phabricator via llvm-commits]

steven.zhang updated this revision to Diff 231175.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D70066/new/

https://reviews.llvm.org/D70066

Files:
  llvm/lib/CodeGen/MacroFusion.cpp
  llvm/test/CodeGen/AArch64/macro-fusion.ll


Index: llvm/test/CodeGen/AArch64/macro-fusion.ll
===================================================================
--- llvm/test/CodeGen/AArch64/macro-fusion.ll
+++ llvm/test/CodeGen/AArch64/macro-fusion.ll
@@ -1,21 +1,18 @@
 ; REQUIRES: asserts
 ; RUN: llc < %s -mtriple=aarch64-linux-gnu -mattr=+fuse-arith-logic -verify-misched -debug-only=machine-scheduler 2>&1 > /dev/null | FileCheck %s
 
-; Verify that, the macro-fusion creates the necessary dependencies between SUs.
+; Verify that, the macro-fusion creates the necessary dependencies between SUs and
+; only 2 SU's are fused at most.
 define signext i32 @test(i32 signext %a, i32 signext %b, i32 signext %c, i32 signext %d) {
 entry:
 ; CHECK: ********** MI Scheduling **********
 ; CHECK-LABEL: %bb.0 entry 
 ; CHECK: Macro fuse: SU([[SU4:[0-9]+]]) - SU([[SU5:[0-9]+]])
 ; CHECK: Bind SU([[SU1:[0-9]+]]) - SU([[SU4]])
-; CHECK: Macro fuse: SU([[SU5]]) - SU([[SU6:[0-9]+]])
-; CHECK: Bind SU([[SU0:[0-9]+]]) - SU([[SU5]])
-; CHECK: SU([[SU0]]):   %{{[0-9]+}}:gpr32 = COPY $w3
+; CHECK-NOT: Macro fuse:
 ; CHECK: SU([[SU1]]):   %{{[0-9]+}}:gpr32 = COPY $w2
 ; CHECK: SU([[SU4]]):   %{{[0-9]+}}:gpr32 = nsw ADDWrr
 ; CHECK: SU([[SU5]]):   %{{[0-9]+}}:gpr32 = nsw ADDWrr
-; CHECK: SU([[SU6]]):   %{{[0-9]+}}:gpr32 = nsw SUBWrr
-
   %add = add nsw i32 %b, %a
   %add1 = add nsw i32 %add, %c
   %sub = sub nsw i32 %add1, %d
Index: llvm/lib/CodeGen/MacroFusion.cpp
===================================================================
--- llvm/lib/CodeGen/MacroFusion.cpp
+++ llvm/lib/CodeGen/MacroFusion.cpp
@@ -32,10 +32,27 @@
 static cl::opt<bool> EnableMacroFusion("misched-fusion", cl::Hidden,
   cl::desc("Enable scheduling for macro fusion."), cl::init(true));
 
+namespace {
+
 static bool isHazard(const SDep &Dep) {
   return Dep.getKind() == SDep::Anti || Dep.getKind() == SDep::Output;
 }
 
+static SUnit *getPredClusterSU(const SUnit &SU) {
+  for (const SDep &SI : SU.Preds)
+    if (SI.isCluster())
+      return SI.getSUnit();
+
+  return nullptr;
+}
+
+static bool hasLessThanNumFused(const SUnit &SU, unsigned FuseLimit) {
+  unsigned Num = 1;
+  const SUnit *CurrentSU = &SU;
+  while ((CurrentSU = getPredClusterSU(*CurrentSU)) && Num < FuseLimit) Num ++;
+  return Num < FuseLimit;
+}
+
 static bool fuseInstructionPair(ScheduleDAGInstrs &DAG, SUnit &FirstSU,
                                 SUnit &SecondSU) {
   // Check that neither instr is already paired with another along the edge
@@ -110,8 +127,6 @@
   return true;
 }
 
-namespace {
-
 /// Post-process the DAG to create cluster edges between instrs that may
 /// be fused by the processor into a single operation.
 class MacroFusion : public ScheduleDAGMutation {
@@ -161,8 +176,10 @@
     if (DepSU.isBoundaryNode())
       continue;
 
+    // Only back-2-back macro fusion is supported now.
     const MachineInstr *DepMI = DepSU.getInstr();
-    if (!shouldScheduleAdjacent(TII, ST, DepMI, AnchorMI))
+    if (!hasLessThanNumFused(DepSU, 2) ||
+        !shouldScheduleAdjacent(TII, ST, DepMI, AnchorMI))
       continue;
 
     if (fuseInstructionPair(DAG, DepSU, AnchorSU))


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