R600/SI: Implement areMemAccessesTriviallyDisjoint

This partially makes up for not having address spaces
used for alias analysis in some simple cases.

This is not yet enabled by default so shouldn't change anything yet.

llvm-svn: 222286

2 files changed, 91 insertions, 0 deletions

diff --git a/llvm/lib/Target/R600/SIInstrInfo.cpp b/llvm/lib/Target/R600/SIInstrInfo.cpp
index 94f7d6920ab..c32c6855a5c 100644
--- a/llvm/lib/Target/R600/SIInstrInfo.cpp
+++ b/llvm/lib/Target/R600/SIInstrInfo.cpp
@@ -23,6 +23,7 @@
 #include "llvm/IR/Function.h"
 #include "llvm/CodeGen/RegisterScavenging.h"
 #include "llvm/MC/MCInstrDesc.h"
+#include "llvm/Support/Debug.h"
 
 using namespace llvm;
 
@@ -832,6 +833,88 @@ SIInstrInfo::isTriviallyReMaterializable(const MachineInstr *MI,
   }
 }
 
+static bool offsetsDoNotOverlap(int WidthA, int OffsetA,
+                                int WidthB, int OffsetB) {
+  int LowOffset = OffsetA < OffsetB ? OffsetA : OffsetB;
+  int HighOffset = OffsetA < OffsetB ? OffsetB : OffsetA;
+  int LowWidth = (LowOffset == OffsetA) ? WidthA : WidthB;
+  return LowOffset + LowWidth <= HighOffset;
+}
+
+bool SIInstrInfo::checkInstOffsetsDoNotOverlap(MachineInstr *MIa,
+                                               MachineInstr *MIb) const {
+  unsigned BaseReg0, Offset0;
+  unsigned BaseReg1, Offset1;
+
+  if (getLdStBaseRegImmOfs(MIa, BaseReg0, Offset0, &RI) &&
+      getLdStBaseRegImmOfs(MIb, BaseReg1, Offset1, &RI)) {
+    assert(MIa->hasOneMemOperand() && MIb->hasOneMemOperand() &&
+           "read2 / write2 not expected here yet");
+    unsigned Width0 = (*MIa->memoperands_begin())->getSize();
+    unsigned Width1 = (*MIb->memoperands_begin())->getSize();
+    if (BaseReg0 == BaseReg1 &&
+        offsetsDoNotOverlap(Width0, Offset0, Width1, Offset1)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+bool SIInstrInfo::areMemAccessesTriviallyDisjoint(MachineInstr *MIa,
+                                                  MachineInstr *MIb,
+                                                  AliasAnalysis *AA) const {
+  unsigned Opc0 = MIa->getOpcode();
+  unsigned Opc1 = MIb->getOpcode();
+
+  assert(MIa && (MIa->mayLoad() || MIa->mayStore()) &&
+         "MIa must load from or modify a memory location");
+  assert(MIb && (MIb->mayLoad() || MIb->mayStore()) &&
+         "MIb must load from or modify a memory location");
+
+  if (MIa->hasUnmodeledSideEffects() || MIb->hasUnmodeledSideEffects())
+    return false;
+
+  // XXX - Can we relax this between address spaces?
+  if (MIa->hasOrderedMemoryRef() || MIb->hasOrderedMemoryRef())
+    return false;
+
+  // TODO: Should we check the address space from the MachineMemOperand? That
+  // would allow us to distinguish objects we know don't alias based on the
+  // underlying addres space, even if it was lowered to a different one,
+  // e.g. private accesses lowered to use MUBUF instructions on a scratch
+  // buffer.
+  if (isDS(Opc0)) {
+    if (isDS(Opc1))
+      return checkInstOffsetsDoNotOverlap(MIa, MIb);
+
+    return !isFLAT(Opc1);
+  }
+
+  if (isMUBUF(Opc0) || isMTBUF(Opc0)) {
+    if (isMUBUF(Opc1) || isMTBUF(Opc1))
+      return checkInstOffsetsDoNotOverlap(MIa, MIb);
+
+    return !isFLAT(Opc1) && !isSMRD(Opc1);
+  }
+
+  if (isSMRD(Opc0)) {
+    if (isSMRD(Opc1))
+      return checkInstOffsetsDoNotOverlap(MIa, MIb);
+
+    return !isFLAT(Opc1) && !isMUBUF(Opc0) && !isMTBUF(Opc0);
+  }
+
+  if (isFLAT(Opc0)) {
+    if (isFLAT(Opc1))
+      return checkInstOffsetsDoNotOverlap(MIa, MIb);
+
+    return false;
+  }
+
+  return false;
+}
+
 namespace llvm {
 namespace AMDGPU {
 // Helper function generated by tablegen.  We are wrapping this with
diff --git a/llvm/lib/Target/R600/SIInstrInfo.h b/llvm/lib/Target/R600/SIInstrInfo.h
index ce32fd7fa65..3bdbc9b5498 100644
--- a/llvm/lib/Target/R600/SIInstrInfo.h
+++ b/llvm/lib/Target/R600/SIInstrInfo.h
@@ -57,6 +57,9 @@ private:
 
   void addDescImplicitUseDef(const MCInstrDesc &Desc, MachineInstr *MI) const;
 
+  bool checkInstOffsetsDoNotOverlap(MachineInstr *MIa,
+                                    MachineInstr *MIb) const;
+
   unsigned findUsedSGPR(const MachineInstr *MI, int OpIndices[3]) const;
 
 public:
@@ -115,6 +118,10 @@ public:
   bool isTriviallyReMaterializable(const MachineInstr *MI,
                                    AliasAnalysis *AA = nullptr) const;
 
+  bool areMemAccessesTriviallyDisjoint(
+    MachineInstr *MIa, MachineInstr *MIb,
+    AliasAnalysis *AA = nullptr) const override;
+
   MachineInstr *buildMovInstr(MachineBasicBlock *MBB,
                               MachineBasicBlock::iterator I,
                               unsigned DstReg, unsigned SrcReg) const override;
@@ -131,6 +138,7 @@ public:
   bool isVOP2(uint16_t Opcode) const;
   bool isVOP3(uint16_t Opcode) const;
   bool isVOPC(uint16_t Opcode) const;
+
   bool isInlineConstant(const APInt &Imm) const;
   bool isInlineConstant(const MachineOperand &MO) const;
   bool isLiteralConstant(const MachineOperand &MO) const;