[Pipeliner] Ignore Artificial dependences while computing recurrences.

[sgundapa]

Summary

The artificial dependencies are not real dependencies. In some cases, they
form circuits with bigger MII. However, they are used to schedule instructions
better.

[MaskRay]

llvm/trunk/test/CodeGen/Hexagon/swp-art-deps-rec.ll

1

Hi, -debug-only= option is only available in #ifdef NDEBUG builds.

This should use REQUIRES: asserts (which I have fixed).

[sgundapa]

Thanks for fixing the unit test.

[jdoerfert]

The test is pretty much full of UB and run with O3, neither is good by itself and together that results in changes anywhere to break this test. D106308 does cause the entire code to be deleted, and that is not the fault of D106308. I will XFAIL this test and you can repair it as you need. FWIW, I'd strongly suggest to *not* run O3 at all as part of such tests.

llvm/trunk/lib/CodeGen/MachinePipeliner.cpp

for (auto &SI : SUnits[i].Succs) {
         int BackEdge = i;
         auto Dep = OutputDeps.find(BackEdge);
         if (Dep != OutputDeps.end()) {
           BackEdge = Dep->second;
           OutputDeps.erase(Dep);
         }
         OutputDeps[N] = BackEdge;
       }
-      // Do not process a boundary node and a back-edge is processed only
-      // if it goes to a Phi.
-      if (SI.getSUnit()->isBoundaryNode() ||
+      // Do not process a boundary node, an artificial node.
+      // A back-edge is processed only if it goes to a Phi.
+      if (SI.getSUnit()->isBoundaryNode() || SI.isArtificial() ||
           (SI.getKind() == SDep::Anti && !SI.getSUnit()->getInstr()->isPHI()))
         continue;
       int N = SI.getSUnit()->NodeNum;
       if (!Added.test(N)) {
         AdjK[i].push_back(N);
         Added.set(N);
       }
     }

llvm/trunk/test/CodeGen/Hexagon/swp-art-deps-rec.ll

+; RUN: llc -march=hexagon -mcpu=hexagonv65 -O3 -debug-only=pipeliner \
+; RUN: < %s 2>&1 | FileCheck %s
+
+; Test that the artificial dependences are ignored while computing the
+; circuits.
+
+; The recurrence should be 1 here. If we do not ignore artificial deps,
+; it will be greater.
+; CHECK: rec=1,
+
+define void @foo(i32 %size) #0 {
+entry:
+  %add = add nsw i32 0, 4
+  %shr = ashr i32 %size, 1
+  br i1 undef, label %L57.us, label %L57.us.ur
+
+L57.us:
+  %R9.0470.us = phi i32 [ %sub40.us.3, %L57.us ], [ undef, %entry ]
+  %sub40.us.3 = add i32 %R9.0470.us, -64
+  br i1 undef, label %L57.us, label %for.cond22.for.end_crit_edge.us.ur-lcssa
+
+for.cond22.for.end_crit_edge.us.ur-lcssa:
+  %inc.us.3.lcssa = phi i32 [ undef, %L57.us ]
+  %sub40.us.3.lcssa = phi i32 [ %sub40.us.3, %L57.us ]
+  %0 = icmp eq i32 %inc.us.3.lcssa, %shr
+  br i1 %0, label %for.cond22.for.end_crit_edge.us, label %L57.us.ur
+
+L57.us.ur:
+  %R15_14.0478.us.ur = phi i64 [ %1, %L57.us.ur ], [ 0, %entry ], [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %R13_12.0477.us.ur = phi i64 [ %14, %L57.us.ur ], [ 0, %entry ], [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %R11_10.0476.us.ur = phi i64 [ %8, %L57.us.ur ], [ 0, %entry ], [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %R7_6.0475.us.ur = phi i64 [ %7, %L57.us.ur ], [ 0, %entry ], [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %R5_4.2474.us.ur = phi i64 [ %16, %L57.us.ur ], [ undef, %entry ], [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %R3_2.0473.us.ur = phi i64 [ %9, %L57.us.ur ], [ 0, %entry ], [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %R1_0.0472.us.ur = phi i64 [ %15, %L57.us.ur ], [ undef, %entry ], [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %kk.0471.us.ur = phi i32 [ %inc.us.ur, %L57.us.ur ], [ 0, %entry ], [ %inc.us.3.lcssa, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %R9.0470.us.ur = phi i32 [ %sub40.us.ur, %L57.us.ur ], [ undef, %entry ], [ %sub40.us.3.lcssa, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %R8.0469.us.ur = phi i32 [ %sub34.us.ur, %L57.us.ur ], [ undef, %entry ], [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ]
+  %1 = tail call i64 @llvm.hexagon.M2.vdmacs.s0(i64 %R15_14.0478.us.ur, i64 %R1_0.0472.us.ur, i64 %R3_2.0473.us.ur)
+  %2 = tail call i64 @llvm.hexagon.S2.shuffeh(i64 %R5_4.2474.us.ur, i64 %R7_6.0475.us.ur)
+  %3 = inttoptr i32 %R9.0470.us.ur to i16*
+  %4 = load i16, i16* %3, align 2
+  %conv27.us.ur = sext i16 %4 to i32
+  %sub28.us.ur = add i32 %R9.0470.us.ur, -8
+  %5 = inttoptr i32 %R8.0469.us.ur to i16*
+  %6 = load i16, i16* %5, align 2
+  %conv30.us.ur = sext i16 %6 to i32
+  %sub31.us.ur = add i32 %R8.0469.us.ur, -8
+  %7 = tail call i64 @llvm.hexagon.A2.combinew(i32 %conv27.us.ur, i32 %conv30.us.ur)
+  %8 = tail call i64 @llvm.hexagon.M2.vdmacs.s0(i64 %R11_10.0476.us.ur, i64 %R1_0.0472.us.ur, i64 %2)
+  %9 = tail call i64 @llvm.hexagon.S2.shuffeh(i64 %7, i64 %R5_4.2474.us.ur)
+  %10 = inttoptr i32 %sub31.us.ur to i16*
+  %11 = load i16, i16* %10, align 2
+  %conv33.us.ur = sext i16 %11 to i32
+  %sub34.us.ur = add i32 %R8.0469.us.ur, -16
+  %conv35.us.ur = trunc i64 %9 to i32
+  %12 = inttoptr i32 %sub28.us.ur to i16*
+  %13 = load i16, i16* %12, align 2
+  %conv39.us.ur = sext i16 %13 to i32
+  %sub40.us.ur = add i32 %R9.0470.us.ur, -16
+  %14 = tail call i64 @llvm.hexagon.M2.vdmacs.s0(i64 %R13_12.0477.us.ur, i64 %R1_0.0472.us.ur, i64 %9)
+  %15 = tail call i64 @llvm.hexagon.A2.combinew(i32 %conv35.us.ur, i32 undef)
+  %16 = tail call i64 @llvm.hexagon.A2.combinew(i32 %conv39.us.ur, i32 %conv33.us.ur)
+  %inc.us.ur = add nsw i32 %kk.0471.us.ur, 1
+  %exitcond535.ur = icmp eq i32 %inc.us.ur, %shr
+  br i1 %exitcond535.ur, label %for.cond22.for.end_crit_edge.us.ur-lcssa572, label %L57.us.ur
+
+for.cond22.for.end_crit_edge.us.ur-lcssa572:
+  %.lcssa730 = phi i64 [ %14, %L57.us.ur ]
+  %.lcssa729 = phi i64 [ %8, %L57.us.ur ]
+  %.lcssa728 = phi i64 [ %1, %L57.us.ur ]
+  %extract.t652 = trunc i64 %.lcssa730 to i32
+  %extract661 = lshr i64 %.lcssa729, 32
+  %extract.t662 = trunc i64 %extract661 to i32
+  %extract.t664 = trunc i64 %.lcssa728 to i32
+  br label %for.cond22.for.end_crit_edge.us
+
+for.cond22.for.end_crit_edge.us:
+  %.lcssa551.off0 = phi i32 [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ], [ %extract.t652, %for.cond22.for.end_crit_edge.us.ur-lcssa572 ]
+  %.lcssa550.off32 = phi i32 [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ], [ %extract.t662, %for.cond22.for.end_crit_edge.us.ur-lcssa572 ]
+  %.lcssa549.off0 = phi i32 [ undef, %for.cond22.for.end_crit_edge.us.ur-lcssa ], [ %extract.t664, %for.cond22.for.end_crit_edge.us.ur-lcssa572 ]
+  %17 = inttoptr i32 %add to i32*
+  store i32 %.lcssa549.off0, i32* %17, align 4
+  %add.ptr61.us = getelementptr inbounds i8, i8* null, i32 32
+  %18 = bitcast i8* %add.ptr61.us to i32*
+  store i32 %.lcssa551.off0, i32* %18, align 4
+  %19 = bitcast i8* undef to i32*
+  store i32 %.lcssa550.off32, i32* %19, align 4
+  call void @llvm.trap()
+  unreachable
+}
+
+; Function Attrs: nounwind readnone
+declare i64 @llvm.hexagon.A2.combinew(i32, i32) #1
+
+; Function Attrs: nounwind readnone
+declare i64 @llvm.hexagon.M2.vdmacs.s0(i64, i64, i64) #1
+
+; Function Attrs: nounwind readnone
+declare i64 @llvm.hexagon.S2.shuffeh(i64, i64) #1
+
+; Function Attrs: noreturn nounwind
+declare void @llvm.trap() #2
+
+attributes #0 = { nounwind }
+attributes #1 = { nounwind readnone }
+attributes #2 = { noreturn nounwind }