implement rdar://6653118 - fastisel should fold loads where possible.

Since mem2reg isn't run at -O0, we get a ton of reloads from the stack,
for example, before, this code:

int foo(int x, int y, int z) {
  return x+y+z;
}

used to compile into:

_foo:                                   ## @foo
	subq	$12, %rsp
	movl	%edi, 8(%rsp)
	movl	%esi, 4(%rsp)
	movl	%edx, (%rsp)
	movl	8(%rsp), %edx
	movl	4(%rsp), %esi
	addl	%edx, %esi
	movl	(%rsp), %edx
	addl	%esi, %edx
	movl	%edx, %eax
	addq	$12, %rsp
	ret

Now we produce:

_foo:                                   ## @foo
	subq	$12, %rsp
	movl	%edi, 8(%rsp)
	movl	%esi, 4(%rsp)
	movl	%edx, (%rsp)
	movl	8(%rsp), %edx
	addl	4(%rsp), %edx    ## Folded load
	addl	(%rsp), %edx     ## Folded load
	movl	%edx, %eax
	addq	$12, %rsp
	ret

Fewer instructions and less register use = faster compiles.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113102 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 70 insertions, 9 deletions

diff --git a/lib/Target/X86/X86FastISel.cpp b/lib/Target/X86/X86FastISel.cpp
index 0c70eec..9390ba9 100644
--- a/lib/Target/X86/X86FastISel.cpp
+++ b/lib/Target/X86/X86FastISel.cpp
@@ -63,6 +63,13 @@ public:
 
   virtual bool TargetSelectInstruction(const Instruction *I);
 
+  /// TryToFoldLoad - The specified machine instr operand is a vreg, and that
+  /// vreg is being provided by the specified load instruction.  If possible,
+  /// try to fold the load as an operand to the instruction, returning true if
+  /// possible.
+  virtual bool TryToFoldLoad(MachineInstr *MI, unsigned OpNo,
+                             const LoadInst *LI);
+  
 #include "X86GenFastISel.inc"
 
 private:
@@ -1941,6 +1948,34 @@ unsigned X86FastISel::TargetMaterializeAlloca(const AllocaInst *C) {
   return ResultReg;
 }
 
+/// TryToFoldLoad - The specified machine instr operand is a vreg, and that
+/// vreg is being provided by the specified load instruction.  If possible,
+/// try to fold the load as an operand to the instruction, returning true if
+/// possible.
+bool X86FastISel::TryToFoldLoad(MachineInstr *MI, unsigned OpNo,
+                                const LoadInst *LI) {
+  X86AddressMode AM;
+  if (!X86SelectAddress(LI->getOperand(0), AM))
+    return false;
+  
+  X86InstrInfo &XII = (X86InstrInfo&)TII;
+  
+  unsigned Size = TD.getTypeAllocSize(LI->getType());
+  unsigned Alignment = LI->getAlignment();
+
+  SmallVector<MachineOperand, 8> AddrOps;
+  AM.getFullAddress(AddrOps);
+  
+  MachineInstr *Result =
+    XII.foldMemoryOperandImpl(*FuncInfo.MF, MI, OpNo, AddrOps, Size, Alignment);
+  if (Result == 0) return false;
+  
+  MI->getParent()->insert(MI, Result);
+  MI->eraseFromParent();
+  return true;
+}
+
+
 namespace llvm {
   llvm::FastISel *X86::createFastISel(FunctionLoweringInfo &funcInfo) {
     return new X86FastISel(funcInfo);
diff --git a/lib/Target/X86/X86InstrBuilder.h b/lib/Target/X86/X86InstrBuilder.h
index 2a6a71d..407b97e 100644
--- a/lib/Target/X86/X86InstrBuilder.h
+++ b/lib/Target/X86/X86InstrBuilder.h
@@ -56,6 +56,31 @@ struct X86AddressMode {
     : BaseType(RegBase), Scale(1), IndexReg(0), Disp(0), GV(0), GVOpFlags(0) {
     Base.Reg = 0;
   }
+  
+  
+  void getFullAddress(SmallVectorImpl<MachineOperand> &MO) {
+    assert(Scale == 1 || Scale == 2 || Scale == 4 || Scale == 8);
+    
+    if (BaseType == X86AddressMode::RegBase)
+      MO.push_back(MachineOperand::CreateReg(Base.Reg, false, false,
+                                             false, false, false, 0, false));
+    else {
+      assert(BaseType == X86AddressMode::FrameIndexBase);
+      MO.push_back(MachineOperand::CreateFI(Base.FrameIndex));
+    }
+    
+    MO.push_back(MachineOperand::CreateImm(Scale));
+    MO.push_back(MachineOperand::CreateReg(IndexReg, false, false,
+                                           false, false, false, 0, false));
+    
+    if (GV)
+      MO.push_back(MachineOperand::CreateGA(GV, Disp, GVOpFlags));
+    else
+      MO.push_back(MachineOperand::CreateImm(Disp));
+    
+    MO.push_back(MachineOperand::CreateReg(0, false, false,
+                                           false, false, false, 0, false));
+  }
 };
 
 /// addDirectMem - This function is used to add a direct memory reference to the
@@ -101,10 +126,11 @@ addFullAddress(const MachineInstrBuilder &MIB,
   
   if (AM.BaseType == X86AddressMode::RegBase)
     MIB.addReg(AM.Base.Reg);
-  else if (AM.BaseType == X86AddressMode::FrameIndexBase)
+  else {
+    assert(AM.BaseType == X86AddressMode::FrameIndexBase);
     MIB.addFrameIndex(AM.Base.FrameIndex);
-  else
-    assert (0);
+  }
+
   MIB.addImm(AM.Scale).addReg(AM.IndexReg);
   if (AM.GV)
     MIB.addGlobalAddress(AM.GV, AM.Disp, AM.GVOpFlags);
diff --git a/lib/Target/X86/X86InstrInfo.h b/lib/Target/X86/X86InstrInfo.h
index f336206..eb0e4b8 100644
--- a/lib/Target/X86/X86InstrInfo.h
+++ b/lib/Target/X86/X86InstrInfo.h
@@ -845,18 +845,18 @@ public:
   /// SetSSEDomain - Set the SSEDomain of MI.
   void SetSSEDomain(MachineInstr *MI, unsigned Domain) const;
 
+  MachineInstr* foldMemoryOperandImpl(MachineFunction &MF,
+                                      MachineInstr* MI,
+                                      unsigned OpNum,
+                                      const SmallVectorImpl<MachineOperand> &MOs,
+                                      unsigned Size, unsigned Alignment) const;
+  
 private:
   MachineInstr * convertToThreeAddressWithLEA(unsigned MIOpc,
                                               MachineFunction::iterator &MFI,
                                               MachineBasicBlock::iterator &MBBI,
                                               LiveVariables *LV) const;
 
-  MachineInstr* foldMemoryOperandImpl(MachineFunction &MF,
-                                     MachineInstr* MI,
-                                     unsigned OpNum,
-                                     const SmallVectorImpl<MachineOperand> &MOs,
-                                     unsigned Size, unsigned Alignment) const;
-
   /// isFrameOperand - Return true and the FrameIndex if the specified
   /// operand and follow operands form a reference to the stack frame.
   bool isFrameOperand(const MachineInstr *MI, unsigned int Op,