Enable splitting indexing from loads with TargetConstants

When I recommitted r208640 (in r216898) I added an exclusion for TargetConstant
offsets, as there is no guarantee that a backend can handle them on generic
ADDs (even if it generates them during address-mode matching) -- and,
specifically, applying this transformation directly with TargetConstants caused
a self-hosting failure on PPC64. Ignoring all TargetConstants, however, is less
than ideal. Instead, for non-opaque constants, we can convert them into regular
constants for use with the generated ADD (or SUB).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216908 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 92ee5c9ea2d1d7a8b6e2d98a1f5f98b345f6edef..1186683aebafd64fb48dfd47d8505b19ba29f7d1 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8029,8 +8029,19 @@ SDValue DAGCombiner::SplitIndexingFromLoad(LoadSDNode *LD) {
   assert(AM != ISD::UNINDEXED);
   SDValue BP = LD->getOperand(1);
   SDValue Inc = LD->getOperand(2);
-  assert(Inc.getOpcode() != ISD::TargetConstant &&
-         "Cannot split out indexing using target constants");
+
+  // Some backends use TargetConstants for load offsets, but don't expect
+  // TargetConstants in general ADD nodes. We can convert these constants into
+  // regular Constants (if the constant is not opaque).
+  assert((Inc.getOpcode() != ISD::TargetConstant ||
+          !cast<ConstantSDNode>(Inc)->isOpaque()) &&
+         "Cannot split out indexing using opaque target constants");
+  if (Inc.getOpcode() == ISD::TargetConstant) {
+    ConstantSDNode *ConstInc = cast<ConstantSDNode>(Inc);
+    Inc = DAG.getConstant(*ConstInc->getConstantIntValue(),
+                          ConstInc->getValueType(0));
+  }
+
   unsigned Opc =
       (AM == ISD::PRE_INC || AM == ISD::POST_INC ? ISD::ADD : ISD::SUB);
   return DAG.getNode(Opc, SDLoc(LD), BP.getSimpleValueType(), BP, Inc);
@@ -8071,16 +8082,18 @@ SDValue DAGCombiner::visitLOAD(SDNode *N) {
       // Indexed loads.
       assert(N->getValueType(2) == MVT::Other && "Malformed indexed loads?");
 
-      // If this load has an TargetConstant offset, then we cannot split the
-      // indexing into an add/sub directly (that TargetConstant may not be
-      // valid for a different type of node).
-      bool HasTCInc = LD->getOperand(2).getOpcode() == ISD::TargetConstant;
+      // If this load has an opaque TargetConstant offset, then we cannot split
+      // the indexing into an add/sub directly (that TargetConstant may not be
+      // valid for a different type of node, and we cannot convert an opaque
+      // target constant into a regular constant).
+      bool HasOTCInc = LD->getOperand(2).getOpcode() == ISD::TargetConstant &&
+                       cast<ConstantSDNode>(LD->getOperand(2))->isOpaque();
 
       if (!N->hasAnyUseOfValue(0) &&
-          ((MaySplitLoadIndex && !HasTCInc) || !N->hasAnyUseOfValue(1))) {
+          ((MaySplitLoadIndex && !HasOTCInc) || !N->hasAnyUseOfValue(1))) {
         SDValue Undef = DAG.getUNDEF(N->getValueType(0));
         SDValue Index;
-        if (N->hasAnyUseOfValue(1) && MaySplitLoadIndex && !HasTCInc) {
+        if (N->hasAnyUseOfValue(1) && MaySplitLoadIndex && !HasOTCInc) {
           Index = SplitIndexingFromLoad(LD);
           // Try to fold the base pointer arithmetic into subsequent loads and
           // stores.

diff --git a/test/CodeGen/PowerPC/split-index-tc.ll b/test/CodeGen/PowerPC/split-index-tc.ll
new file mode 100644 (file)
index 0000000..03aff24
--- /dev/null
+++ b/test/CodeGen/PowerPC/split-index-tc.ll
@@ -0,0 +1,82 @@
+; RUN: llc -mcpu=pwr7 < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+%"class.llvm::MachineOperand" = type { i8, [3 x i8], i64, i64*, i64 }
+
+; Function Attrs: nounwind
+define void @_ZN4llvm17ScheduleDAGInstrs14addPhysRegDepsEPNS_5SUnitEj() #0 align 2 {
+
+; If we were able to split out the indexing, the load with update should be
+; removed (resulting in a nearly-empty output).
+; CHECK-LABEL: @_ZN4llvm17ScheduleDAGInstrs14addPhysRegDepsEPNS_5SUnitEj
+; CHECK-NOT: lhzu
+
+entry:
+  %0 = load %"class.llvm::MachineOperand"** undef, align 8
+  br i1 undef, label %_ZNK4llvm14MachineOperand6getRegEv.exit, label %cond.false.i123
+
+cond.false.i123:                                  ; preds = %_ZN4llvm12MachineInstr10getOperandEj.exit
+  unreachable
+
+_ZNK4llvm14MachineOperand6getRegEv.exit:          ; preds = %_ZN4llvm12MachineInstr10getOperandEj.exit
+  %IsDef.i = getelementptr inbounds %"class.llvm::MachineOperand"* %0, i64 undef, i32 1
+  %1 = bitcast [3 x i8]* %IsDef.i to i24*
+  %bf.load.i = load i24* %1, align 1
+  %2 = and i24 %bf.load.i, 128
+  br i1 undef, label %for.cond.cleanup, label %for.body.lr.ph
+
+for.body.lr.ph:                                   ; preds = %_ZNK4llvm14MachineOperand6getRegEv.exit
+  %3 = zext i24 %2 to i32
+  br i1 undef, label %cond.false.i134, label %_ZNK4llvm18MCRegAliasIteratordeEv.exit
+
+for.cond.cleanup:                                 ; preds = %_ZNK4llvm14MachineOperand6getRegEv.exit
+  br i1 undef, label %_ZNK4llvm14MachineOperand5isDefEv.exit, label %cond.false.i129
+
+cond.false.i129:                                  ; preds = %for.cond.cleanup
+  unreachable
+
+_ZNK4llvm14MachineOperand5isDefEv.exit:           ; preds = %for.cond.cleanup
+  br i1 undef, label %_ZNK4llvm14MachineOperand6getRegEv.exit247, label %cond.false.i244
+
+cond.false.i134:                                  ; preds = %for.body.lr.ph
+  unreachable
+
+_ZNK4llvm18MCRegAliasIteratordeEv.exit:           ; preds = %for.body.lr.ph
+  unreachable
+
+cond.false.i244:                                  ; preds = %_ZNK4llvm14MachineOperand5isDefEv.exit
+  unreachable
+
+_ZNK4llvm14MachineOperand6getRegEv.exit247:       ; preds = %_ZNK4llvm14MachineOperand5isDefEv.exit
+  br i1 undef, label %if.then53, label %if.end55
+
+if.then53:                                        ; preds = %_ZNK4llvm14MachineOperand6getRegEv.exit247
+  unreachable
+
+if.end55:                                         ; preds = %_ZNK4llvm14MachineOperand6getRegEv.exit247
+  br i1 undef, label %_ZNK4llvm14MachineOperand6isDeadEv.exit262, label %cond.false.i257
+
+cond.false.i257:                                  ; preds = %if.end55
+  unreachable
+
+_ZNK4llvm14MachineOperand6isDeadEv.exit262:       ; preds = %if.end55
+  %bf.load.i259 = load i24* %1, align 1
+  br i1 undef, label %if.then57, label %if.else59
+
+if.then57:                                        ; preds = %_ZNK4llvm14MachineOperand6isDeadEv.exit262
+  unreachable
+
+if.else59:                                        ; preds = %_ZNK4llvm14MachineOperand6isDeadEv.exit262
+  br i1 undef, label %if.end89, label %if.then62
+
+if.then62:                                        ; preds = %if.else59
+  unreachable
+
+if.end89:                                         ; preds = %if.else59
+  unreachable
+}
+
+attributes #0 = { nounwind }
+
+