[SystemZ] Remove no-op MVCs

The stack coloring pass has code to delete stores and loads that become
trivially dead after coloring.  Extend it to cope with single instructions
that copy from one frame index to another.

The testcase happens to show an example of this kicking in at the moment.
It did occur in Real Code too though.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185705 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Target/TargetInstrInfo.h b/include/llvm/Target/TargetInstrInfo.h
index 7172eb0b6804cd56b0bf350e723499da0a1aa585..f746daf921b8ae1ec64d36bf5bfe82507fc6e85c 100644 (file)
--- a/include/llvm/Target/TargetInstrInfo.h
+++ b/include/llvm/Target/TargetInstrInfo.h
@@ -173,6 +173,14 @@ public:
                                    const MachineMemOperand *&MMO,
                                    int &FrameIndex) const;
 
+  /// isStackSlotCopy - Return true if the specified machine instruction
+  /// is a copy of one stack slot to another and has no other effect.
+  /// Provide the identity of the two frame indices.
+  virtual bool isStackSlotCopy(const MachineInstr *MI, int &DestFrameIndex,
+                               int &SrcFrameIndex) const {
+    return false;
+  }
+
   /// reMaterialize - Re-issue the specified 'original' instruction at the
   /// specific location targeting a new destination register.
   /// The register in Orig->getOperand(0).getReg() will be substituted by

diff --git a/lib/CodeGen/StackSlotColoring.cpp b/lib/CodeGen/StackSlotColoring.cpp
index e1b63680e021b2f75127c552e06ff3272cc0c49a..d0c9e1d677b86c5e7792482189a2ee46a01da2e6 100644 (file)
--- a/lib/CodeGen/StackSlotColoring.cpp
+++ b/lib/CodeGen/StackSlotColoring.cpp
@@ -377,10 +377,19 @@ bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
     if (DCELimit != -1 && (int)NumDead >= DCELimit)
       break;
 
+    int FirstSS, SecondSS;
+    if (TII->isStackSlotCopy(I, FirstSS, SecondSS) &&
+        FirstSS == SecondSS &&
+        FirstSS != -1) {
+      ++NumDead;
+      changed = true;
+      toErase.push_back(I);
+      continue;
+    }
+        
     MachineBasicBlock::iterator NextMI = llvm::next(I);
     if (NextMI == MBB->end()) continue;
 
-    int FirstSS, SecondSS;
     unsigned LoadReg = 0;
     unsigned StoreReg = 0;
     if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;

diff --git a/lib/Target/SystemZ/SystemZInstrInfo.cpp b/lib/Target/SystemZ/SystemZInstrInfo.cpp
index 81d72e05740f3343088ffc1a0227abb176b69414..cfd270ae43470d1a8444c112d440c64e1664fb1f 100644 (file)
--- a/lib/Target/SystemZ/SystemZInstrInfo.cpp
+++ b/lib/Target/SystemZ/SystemZInstrInfo.cpp
@@ -104,6 +104,31 @@ unsigned SystemZInstrInfo::isStoreToStackSlot(const MachineInstr *MI,
   return isSimpleMove(MI, FrameIndex, SystemZII::SimpleBDXStore);
 }
 
+bool SystemZInstrInfo::isStackSlotCopy(const MachineInstr *MI,
+                                       int &DestFrameIndex,
+                                       int &SrcFrameIndex) const {
+  // Check for MVC 0(Length,FI1),0(FI2)
+  const MachineFrameInfo *MFI = MI->getParent()->getParent()->getFrameInfo();
+  if (MI->getOpcode() != SystemZ::MVC ||
+      !MI->getOperand(0).isFI() ||
+      MI->getOperand(1).getImm() != 0 ||
+      !MI->getOperand(3).isFI() ||
+      MI->getOperand(4).getImm() != 0)
+    return false;
+
+  // Check that Length covers the full slots.
+  int64_t Length = MI->getOperand(2).getImm();
+  unsigned FI1 = MI->getOperand(0).getIndex();
+  unsigned FI2 = MI->getOperand(3).getIndex();
+  if (MFI->getObjectSize(FI1) != Length ||
+      MFI->getObjectSize(FI2) != Length)
+    return false;
+
+  DestFrameIndex = FI1;
+  SrcFrameIndex = FI2;
+  return true;
+}
+
 bool SystemZInstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,
                                      MachineBasicBlock *&TBB,
                                      MachineBasicBlock *&FBB,

diff --git a/lib/Target/SystemZ/SystemZInstrInfo.h b/lib/Target/SystemZ/SystemZInstrInfo.h
index 11d486cafbaa52a60a3e2be5ca3c8a717c94738e..3fe71d88547dfbf3089f02eb33726a3fd4f2fece 100644 (file)
--- a/lib/Target/SystemZ/SystemZInstrInfo.h
+++ b/lib/Target/SystemZ/SystemZInstrInfo.h
@@ -91,6 +91,8 @@ public:
                                        int &FrameIndex) const LLVM_OVERRIDE;
   virtual unsigned isStoreToStackSlot(const MachineInstr *MI,
                                       int &FrameIndex) const LLVM_OVERRIDE;
+  virtual bool isStackSlotCopy(const MachineInstr *MI, int &DestFrameIndex,
+                               int &SrcFrameIndex) const LLVM_OVERRIDE;
   virtual bool AnalyzeBranch(MachineBasicBlock &MBB,
                              MachineBasicBlock *&TBB,
                              MachineBasicBlock *&FBB,

diff --git a/test/CodeGen/SystemZ/spill-01.ll b/test/CodeGen/SystemZ/spill-01.ll
index b2d9fe7be4a83768b4877e69122ad2ae07d11605..d48e9827f52f59b89c9a2b8a3aea80807347a5bd 100644 (file)
--- a/test/CodeGen/SystemZ/spill-01.ll
+++ b/test/CodeGen/SystemZ/spill-01.ll
@@ -456,3 +456,92 @@ skip:
 
   ret void
 }
+
+; This used to generate a no-op MVC.  It is very sensitive to spill heuristics.
+define void @f11() {
+; CHECK: f11:
+; CHECK-NOT: mvc [[OFFSET:[0-9]+]](8,%r15), [[OFFSET]](%r15)
+; CHECK: br %r14
+entry:
+  %val0 = load volatile i64 *@h0
+  %val1 = load volatile i64 *@h1
+  %val2 = load volatile i64 *@h2
+  %val3 = load volatile i64 *@h3
+  %val4 = load volatile i64 *@h4
+  %val5 = load volatile i64 *@h5
+  %val6 = load volatile i64 *@h6
+  %val7 = load volatile i64 *@h7
+
+  %altval0 = load volatile i64 *@h0
+  %altval1 = load volatile i64 *@h1
+
+  call void @foo()
+
+  store volatile i64 %val0, i64 *@h0
+  store volatile i64 %val1, i64 *@h1
+  store volatile i64 %val2, i64 *@h2
+  store volatile i64 %val3, i64 *@h3
+  store volatile i64 %val4, i64 *@h4
+  store volatile i64 %val5, i64 *@h5
+  store volatile i64 %val6, i64 *@h6
+  store volatile i64 %val7, i64 *@h7
+
+  %check = load volatile i64 *@h0
+  %cond = icmp eq i64 %check, 0
+  br i1 %cond, label %a1, label %b1
+
+a1:
+  call void @foo()
+  br label %join1
+
+b1:
+  call void @foo()
+  br label %join1
+
+join1:
+  %newval0 = phi i64 [ %val0, %a1 ], [ %altval0, %b1 ]
+
+  call void @foo()
+
+  store volatile i64 %val1, i64 *@h1
+  store volatile i64 %val2, i64 *@h2
+  store volatile i64 %val3, i64 *@h3
+  store volatile i64 %val4, i64 *@h4
+  store volatile i64 %val5, i64 *@h5
+  store volatile i64 %val6, i64 *@h6
+  store volatile i64 %val7, i64 *@h7
+  br i1 %cond, label %a2, label %b2
+
+a2:
+  call void @foo()
+  br label %join2
+
+b2:
+  call void @foo()
+  br label %join2
+
+join2:
+  %newval1 = phi i64 [ %val1, %a2 ], [ %altval1, %b2 ]
+
+  call void @foo()
+
+  store volatile i64 %val2, i64 *@h2
+  store volatile i64 %val3, i64 *@h3
+  store volatile i64 %val4, i64 *@h4
+  store volatile i64 %val5, i64 *@h5
+  store volatile i64 %val6, i64 *@h6
+  store volatile i64 %val7, i64 *@h7
+
+  call void @foo()
+
+  store volatile i64 %newval0, i64 *@h0
+  store volatile i64 %newval1, i64 *@h1
+  store volatile i64 %val2, i64 *@h2
+  store volatile i64 %val3, i64 *@h3
+  store volatile i64 %val4, i64 *@h4
+  store volatile i64 %val5, i64 *@h5
+  store volatile i64 %val6, i64 *@h6
+  store volatile i64 %val7, i64 *@h7
+
+  ret void
+}