[PATCH] D105996: [AArch64] Enable Upper bound unrolling universally

[JinGu Kang via Phabricator via llvm-commits]

jaykang10 created this revision.
jaykang10 added reviewers: SjoerdMeijer, dmgreen, NickGuy, sanwou01.
Herald added subscribers: danielkiss, zzheng, hiraditya, kristof.beyls.
jaykang10 requested review of this revision.
Herald added a project: LLVM.
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On the attached test, the LoopUnrollPass fails to unroll the loop because its trip count is not constant. `%0 = select i1 %cond, i32 2, i32 3` 
In order to unroll the loop, we need to set up `UP.UpperBound = true` in `getUnrollingPreferences`.
Currently, it is enabled with certain target condition on AArch64 target. This patch enables it universally for AArch64 target.

The performance data from spec2017 is as below.

  Benchmark		diff (%)
  500.perlbench_r		1.226130632
  502.gcc_r		0.22529927
  505.mcf_r		0.00061882
  520.omnetpp_r		-0.094707343
  523.xalancbmk_r		-0.125968029
  525.x264_r		0.45726427
  531.deepsjeng_r		0.326290873
  541.leela_r		-0.047175519
  548.exchange2_r		0.101954068
  557.xz_r		0.275802637


https://reviews.llvm.org/D105996

Files:
  llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
  llvm/test/Transforms/LoopUnroll/AArch64/unroll-upperbound.ll


Index: llvm/test/Transforms/LoopUnroll/AArch64/unroll-upperbound.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopUnroll/AArch64/unroll-upperbound.ll
@@ -0,0 +1,56 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -loop-unroll -mtriple aarch64 | FileCheck %s
+
+%struct.info = type { i32, i32*, i32* }
+
+ at state = external dso_local local_unnamed_addr global %struct.info*, align 8
+ at slab = external dso_local local_unnamed_addr global %struct.info*, align 8
+
+define void @test(%struct.info* %reginfo, i1 %cond) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    switch i32 0, label [[FOR_BODY_IF_END6_CRIT_EDGE:%.*]] [
+; CHECK-NEXT:    i32 2, label [[IF_THEN4:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       for.body.if.end6_crit_edge:
+; CHECK-NEXT:    unreachable
+; CHECK:       if.then4:
+; CHECK-NEXT:    br i1 false, label [[FOR_END:%.*]], label [[FOR_BODY_1:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+; CHECK:       for.body.1:
+; CHECK-NEXT:    switch i32 1, label [[FOR_BODY_IF_END6_CRIT_EDGE]] [
+; CHECK-NEXT:    i32 2, label [[IF_THEN4_1:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       if.then4.1:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[FOR_END]], label [[FOR_BODY_2:%.*]]
+; CHECK:       for.body.2:
+; CHECK-NEXT:    switch i32 2, label [[FOR_BODY_IF_END6_CRIT_EDGE]] [
+; CHECK-NEXT:    i32 2, label [[IF_THEN4_2:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       if.then4.2:
+; CHECK-NEXT:    br label [[FOR_END]]
+;
+entry:
+  %0 = select i1 %cond, i32 2, i32 3
+  br label %for.body
+
+for.body:                                         ; preds = %if.then4, %entry
+  %i.017 = phi i32 [ 0, %entry ], [ %inc, %if.then4 ]
+  switch i32 %i.017, label %for.body.if.end6_crit_edge [
+  i32 2, label %if.then4
+  ]
+
+for.body.if.end6_crit_edge:                       ; preds = %for.body
+  unreachable
+
+if.then4:                                         ; preds = %for.body
+  %inc = add nuw nsw i32 %i.017, 1
+  %exitcond.not = icmp eq i32 %inc, %0
+  br i1 %exitcond.not, label %for.end, label %for.body
+
+for.end:                                          ; preds = %if.then4
+  ret void
+}
Index: llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -1568,6 +1568,10 @@
   // Enable partial unrolling and runtime unrolling.
   BaseT::getUnrollingPreferences(L, SE, UP);
 
+  // Enable Upper bound unrolling universally, not dependant upon the conditions
+  // below.
+  UP.UpperBound = true;
+
   // For inner loop, it is more likely to be a hot one, and the runtime check
   // can be promoted out from LICM pass, so the overhead is less, let's try
   // a larger threshold to unroll more loops.
@@ -1608,7 +1612,6 @@
       !ST->getSchedModel().isOutOfOrder()) {
     UP.Runtime = true;
     UP.Partial = true;
-    UP.UpperBound = true;
     UP.UnrollRemainder = true;
     UP.DefaultUnrollRuntimeCount = 4;
 


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