[Codegen][X86][AArch64][ARM][PowerPC] Inc-of-add vs sub-of-not (PR42457)

Summary:
This is the backend part of [[ https://bugs.llvm.org/show_bug.cgi?id=42457 | PR42457 ]].
In middle-end, we'd want to prefer the form with two adds - D63992,
but as this diff shows, not every target will prefer that pattern.

Out of 4 targets for which i added tests all seem to be ok with inc-of-add for scalars,
but only X86 prefer that same pattern for vectors.

Here i'm adding a new TLI hook, always defaulting to the inc-of-add,
but adding AArch64,ARM,PowerPC overrides to prefer inc-of-add only for scalars.

Reviewers: spatel, RKSimon, efriedma, t.p.northover, hfinkel

Reviewed By: efriedma

Subscribers: nemanjai, javed.absar, kristof.beyls, kbarton, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64090

llvm-svn: 365010

6 files changed, 25 insertions, 0 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 515da93cded..11ee1a5f9e6 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -12039,6 +12039,11 @@ bool AArch64TargetLowering::isIntDivCheap(EVT VT, AttributeList Attr) const {
   return OptSize && !VT.isVector();
 }
 
+bool AArch64TargetLowering::preferIncOfAddToSubOfNot(EVT VT) const {
+  // We want inc-of-add for scalars and sub-of-not for vectors.
+  return VT.isScalarInteger();
+}
+
 bool AArch64TargetLowering::enableAggressiveFMAFusion(EVT VT) const {
   return Subtarget->hasAggressiveFMA() && VT.isFloatingPoint();
 }
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.h b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
index 94793c678ae..754caaf5192 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.h
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
@@ -497,6 +497,8 @@ public:
     return VTIsOk(XVT) && VTIsOk(KeptBitsVT);
   }
 
+  bool preferIncOfAddToSubOfNot(EVT VT) const override;
+
   bool hasBitPreservingFPLogic(EVT VT) const override {
     // FIXME: Is this always true? It should be true for vectors at least.
     return VT == MVT::f32 || VT == MVT::f64;
diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index efa97b4200f..c1668dcb5b7 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -10736,6 +10736,15 @@ bool ARMTargetLowering::shouldFoldConstantShiftPairToMask(
   return false;
 }
 
+bool ARMTargetLowering::preferIncOfAddToSubOfNot(EVT VT) const {
+  if (!Subtarget->hasNEON()) {
+    if (Subtarget->isThumb1Only())
+      return VT.getScalarSizeInBits() <= 32;
+    return true;
+  }
+  return VT.isScalarInteger();
+}
+
 static SDValue PerformSHLSimplify(SDNode *N,
                                 TargetLowering::DAGCombinerInfo &DCI,
                                 const ARMSubtarget *ST) {
diff --git a/llvm/lib/Target/ARM/ARMISelLowering.h b/llvm/lib/Target/ARM/ARMISelLowering.h
index d188ad2facb..906e10d5f4c 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.h
+++ b/llvm/lib/Target/ARM/ARMISelLowering.h
@@ -608,6 +608,9 @@ class VectorType;
 
     bool shouldFoldConstantShiftPairToMask(const SDNode *N,
                                            CombineLevel Level) const override;
+
+    bool preferIncOfAddToSubOfNot(EVT VT) const override;
+
   protected:
     std::pair<const TargetRegisterClass *, uint8_t>
     findRepresentativeClass(const TargetRegisterInfo *TRI,
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index b1ff161a4cb..aad7ef6ef68 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -1279,6 +1279,10 @@ bool PPCTargetLowering::hasSPE() const {
   return Subtarget.hasSPE();
 }
 
+bool PPCTargetLowering::preferIncOfAddToSubOfNot(EVT VT) const {
+  return VT.isScalarInteger();
+}
+
 const char *PPCTargetLowering::getTargetNodeName(unsigned Opcode) const {
   switch ((PPCISD::NodeType)Opcode) {
   case PPCISD::FIRST_NUMBER:    break;
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 2c0ac80d95b..73c6dcd7c85 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -634,6 +634,8 @@ namespace llvm {
       return true;
     }
 
+    bool preferIncOfAddToSubOfNot(EVT VT) const override;
+
     bool convertSetCCLogicToBitwiseLogic(EVT VT) const override {
       return VT.isScalarInteger();
     }