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

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This is the example:

int foo(int a, int b, int c, int d) {
  return a + b + c + d;
}

And this is the Dependency Graph:
+------+       +------+       +------+       +------+
|  A   |       |  B   |       |  C   |       |  D   |
+--+--++       +---+--+       +--+---+       +--+---+
   ^  ^            ^  ^          ^              ^
   |  |            |  |          |              |
   |  |            |  |New1      +--------------+
   |  |            |  |          |
   |  |            |  |       +--+---+
   |  |New2        |  +-------+ ADD1 |
   |  |            |          +--+---+
   |  |            |    Fuse     ^
   |  |            +-------------+
   |  +------------+
   |               |
   |   Fuse     +--+---+
   +----------->+ ADD2 |
   |            +------+
+--+---+
| ADD3 |
+------+

We need also create an artificial edge from ADD1 to A if
https://reviews.llvm.org/D69998 is landed. That will force the Node A scheduled
before the ADD1 and ADD2. But in fact, it is ok to schedule the Node A
in-between ADD3 and ADD2, as ADD3 and ADD2 are NOT a fusion pair because
ADD2 has been matched to ADD1. We are creating these unnecessary dependency
edges that override the heuristics.

Differential Revision: https://reviews.llvm.org/D70066
This commit is contained in:
QingShan Zhang
2019-12-04 04:58:34 +00:00
parent f0ba1aec35
commit d84b320dfd
2 changed files with 21 additions and 7 deletions
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19
llvm/lib/CodeGen/MacroFusion.cpp
View File

@@ -36,6 +36,21 @@ 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
@@ -161,8 +176,10 @@ bool MacroFusion::scheduleAdjacentImpl(ScheduleDAGInstrs &DAG, SUnit &AnchorSU)
if (DepSU.isBoundaryNode())
continue;
// Only chain two instructions together at most.
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))

9
llvm/test/CodeGen/AArch64/macro-fusion.ll
View File

@@ -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