X86 Peephole: fold loads to the source register operand if possible.

Machine CSE and other optimizations can remove instructions so folding
is possible at peephole while not possible at ISel.

rdar://10554090 and rdar://11873276


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160919 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetInstrInfo.h

@@ -14,6 +14,7 @@
 #ifndef LLVM_TARGET_TARGETINSTRINFO_H
 #define LLVM_TARGET_TARGETINSTRINFO_H
 
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/CodeGen/DFAPacketizer.h"
 #include "llvm/CodeGen/MachineFunction.h"
@@ -693,6 +694,16 @@ public:
     return false;
   }
 
+  /// optimizeLoadInstr - Try to remove the load by folding it to a register
+  /// operand at the use. We fold the load instructions if and only if the
+  /// def and use are in the same BB.
+  virtual MachineInstr* optimizeLoadInstr(MachineInstr *MI,
+                        const MachineRegisterInfo *MRI,
+                        SmallSet<unsigned, 4> &FoldAsLoadDefRegs,
+                        MachineInstr *&DefMI) const {
+    return 0;
+  }
+
   /// FoldImmediate - 'Reg' is known to be defined by a move immediate
   /// instruction, try to fold the immediate into the use instruction.
   virtual bool FoldImmediate(MachineInstr *UseMI, MachineInstr *DefMI,

lib/CodeGen/PeepholeOptimizer.cpp

@@ -78,6 +78,7 @@ STATISTIC(NumReuse,      "Number of extension results reused");
 STATISTIC(NumBitcasts,   "Number of bitcasts eliminated");
 STATISTIC(NumCmps,       "Number of compares eliminated");
 STATISTIC(NumImmFold,    "Number of move immediate folded");
+STATISTIC(NumLoadFold,   "Number of loads folded");
 
 namespace {
   class PeepholeOptimizer : public MachineFunctionPass {
@@ -441,6 +442,7 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
   SmallPtrSet<MachineInstr*, 8> LocalMIs;
   SmallSet<unsigned, 4> ImmDefRegs;
   DenseMap<unsigned, MachineInstr*> ImmDefMIs;
+  SmallSet<unsigned, 4> FoldAsLoadDefRegs;
   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
     MachineBasicBlock *MBB = &*I;
 
@@ -448,6 +450,7 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
     LocalMIs.clear();
     ImmDefRegs.clear();
     ImmDefMIs.clear();
+    FoldAsLoadDefRegs.clear();
 
     bool First = true;
     MachineBasicBlock::iterator PMII;
@@ -489,6 +492,25 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
           Changed |= foldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs);
       }
 
+      MachineInstr *DefMI = 0;
+      MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI, FoldAsLoadDefRegs,
+                                                    DefMI);
+      if (FoldMI) {
+        // Update LocalMIs since we replaced MI with FoldMI and deleted DefMI.
+        LocalMIs.erase(MI);
+        LocalMIs.erase(DefMI);
+        LocalMIs.insert(FoldMI);
+        MI->eraseFromParent();
+        DefMI->eraseFromParent();
+        ++NumLoadFold;
+
+        // MI is replaced with FoldMI.
+        Changed = true;
+        PMII = FoldMI;
+        MII = llvm::next(PMII);
+        continue;
+      }
+
       First = false;
       PMII = MII;
       ++MII;

lib/Target/X86/X86InstrInfo.cpp

@@ -3323,6 +3323,75 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2,
   return true;
 }
 
+/// optimizeLoadInstr - Try to remove the load by folding it to a register
+/// operand at the use. We fold the load instructions if and only if the
+/// def and use are in the same BB.
+MachineInstr* X86InstrInfo::
+optimizeLoadInstr(MachineInstr *MI, const MachineRegisterInfo *MRI,
+                  SmallSet<unsigned, 4> &FoldAsLoadDefRegs,
+                  MachineInstr *&DefMI) const {
+  if (MI->mayStore() || MI->isCall())
+    // To be conservative, we don't fold the loads if there is a store in
+    // between.
+    FoldAsLoadDefRegs.clear();
+  // We only fold loads to a virtual register.
+  if (MI->canFoldAsLoad()) {
+    const MCInstrDesc &MCID = MI->getDesc();
+    if (MCID.getNumDefs() == 1) {
+      unsigned Reg = MI->getOperand(0).getReg();
+      // To reduce compilation time, we check MRI->hasOneUse when inserting
+      // loads. It should be checked when processing uses of the load, since
+      // uses can be removed during peephole.
+      if (TargetRegisterInfo::isVirtualRegister(Reg) && MRI->hasOneUse(Reg)) {
+        FoldAsLoadDefRegs.insert(Reg);
+        return 0;
+      }
+    }
+  }
+
+  // Collect information about virtual register operands of MI.
+  DenseMap<unsigned, unsigned> SrcVirtualRegToOp;
+  SmallSet<unsigned, 4> DstVirtualRegs;
+  for (unsigned i = 0, e = MI->getDesc().getNumOperands(); i != e; ++i) {
+    MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isReg())
+      continue;
+    unsigned Reg = MO.getReg();
+    if (!TargetRegisterInfo::isVirtualRegister(Reg))
+      continue;
+    if (MO.isDef())
+      DstVirtualRegs.insert(Reg);
+    else if (FoldAsLoadDefRegs.count(Reg)) {
+      // Only handle the case where Reg is used in a single src operand.
+      if (SrcVirtualRegToOp.find(Reg) != SrcVirtualRegToOp.end())
+        SrcVirtualRegToOp.erase(Reg);
+      else
+        SrcVirtualRegToOp.insert(std::make_pair(Reg, i));
+    }
+  }
+
+  for (DenseMap<unsigned, unsigned>::iterator SI = SrcVirtualRegToOp.begin(),
+       SE = SrcVirtualRegToOp.end(); SI != SE; SI++) {
+    // If the virtual register is updated by MI, we can't fold the load.
+    if (DstVirtualRegs.count(SI->first)) continue;
+
+    // Check whether we can fold the def into this operand.
+    DefMI = MRI->getVRegDef(SI->first);
+    assert(DefMI);
+    bool SawStore = false;
+    if (!DefMI->isSafeToMove(this, 0, SawStore))
+       continue;
+
+    SmallVector<unsigned, 8> Ops;
+    Ops.push_back(SI->second);
+    MachineInstr *FoldMI = foldMemoryOperand(MI, Ops, DefMI);
+    if (!FoldMI) continue;
+    FoldAsLoadDefRegs.erase(SI->first);
+    return FoldMI;
+  }
+  return 0;
+}
+
 /// Expand2AddrUndef - Expand a single-def pseudo instruction to a two-addr
 /// instruction with two undef reads of the register being defined.  This is
 /// used for mapping:

lib/Target/X86/X86InstrInfo.h

@@ -387,6 +387,14 @@ public:
                                     unsigned SrcReg2, int CmpMask, int CmpValue,
                                     const MachineRegisterInfo *MRI) const;
 
+  /// optimizeLoadInstr - Try to remove the load by folding it to a register
+  /// operand at the use. We fold the load instructions if and only if the
+  /// def and use are in the same BB.
+  virtual MachineInstr* optimizeLoadInstr(MachineInstr *MI,
+                        const MachineRegisterInfo *MRI,
+                        SmallSet<unsigned, 4> &FoldAsLoadDefRegs,
+                        MachineInstr *&DefMI) const;
+
 private:
   MachineInstr * convertToThreeAddressWithLEA(unsigned MIOpc,
                                               MachineFunction::iterator &MFI,

test/CodeGen/X86/2012-05-19-avx2-store.ll

@@ -3,8 +3,7 @@
 define void @double_save(<4 x i32>* %Ap, <4 x i32>* %Bp, <8 x i32>* %P) nounwind ssp {
 entry:
   ; CHECK: vmovaps
-  ; CHECK: vmovaps
+  ; CHECK: vinsertf128 $1, ([[A0:%rdi|%rsi]]),
-  ; CHECK: vinsertf128
   ; CHECK: vmovups
   %A = load <4 x i32>* %Ap
   %B = load <4 x i32>* %Bp

test/CodeGen/X86/break-sse-dep.ll

@@ -34,8 +34,7 @@ entry:
 define double @squirt(double* %x) nounwind {
 entry:
 ; CHECK: squirt:
-; CHECK: movsd ([[A0]]), %xmm0
+; CHECK: sqrtsd ([[A0]]), %xmm0
-; CHECK: sqrtsd %xmm0, %xmm0
   %z = load double* %x
   %t = call double @llvm.sqrt.f64(double %z)
   ret double %t

test/CodeGen/X86/fold-load.ll

@@ -45,3 +45,29 @@ L:
 
 }
 
+; rdar://10554090
+; xor in exit block will be CSE'ed and load will be folded to xor in entry.
+define i1 @test3(i32* %P, i32* %Q) nounwind {
+; CHECK: test3:
+; CHECK: movl 8(%esp), %eax
+; CHECK: xorl (%eax),
+; CHECK: j
+; CHECK-NOT: xor
+entry:
+  %0 = load i32* %P, align 4
+  %1 = load i32* %Q, align 4
+  %2 = xor i32 %0, %1
+  %3 = and i32 %2, 65535
+  %4 = icmp eq i32 %3, 0
+  br i1 %4, label %exit, label %land.end
+
+exit:
+  %shr.i.i19 = xor i32 %1, %0
+  %5 = and i32 %shr.i.i19, 2147418112
+  %6 = icmp eq i32 %5, 0
+  br label %land.end
+
+land.end:
+  %7 = phi i1 [ %6, %exit ], [ false, %entry ]
+  ret i1 %7
+}

test/CodeGen/X86/fold-pcmpeqd-1.ll

@@ -1,11 +1,14 @@
-; RUN: llc < %s -march=x86 -mattr=+sse2 > %t
+; RUN: llc < %s -march=x86 -mattr=+sse2 | FileCheck %s
-; RUN: grep pcmpeqd %t | count 1
-; RUN: grep xor %t | count 1
-; RUN: not grep LCP %t
 
 define <2 x double> @foo() nounwind {
   ret <2 x double> bitcast (<2 x i64><i64 -1, i64 -1> to <2 x double>)
+; CHECK: foo:
+; CHECK: pcmpeqd %xmm{{[0-9]+}}, %xmm{{[0-9]+}}
+; CHECK-NEXT: ret
 }
 define <2 x double> @bar() nounwind {
   ret <2 x double> bitcast (<2 x i64><i64 0, i64 0> to <2 x double>)
+; CHECK: bar:
+; CHECK: xorps %xmm{{[0-9]+}}, %xmm{{[0-9]+}}
+; CHECK-NEXT: ret
 }

test/CodeGen/X86/sse-minmax.ll

@@ -137,16 +137,13 @@ define double @ole_inverse(double %x, double %y) nounwind {
 }
 
 ; CHECK:      ogt_x:
-; CHECK-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; CHECK-NEXT: maxsd LCP{{.*}}(%rip), %xmm0
-; CHECK-NEXT: maxsd %xmm1, %xmm0
 ; CHECK-NEXT: ret
 ; UNSAFE:      ogt_x:
-; UNSAFE-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; UNSAFE-NEXT: maxsd LCP{{.*}}(%rip), %xmm0
-; UNSAFE-NEXT: maxsd %xmm1, %xmm0
 ; UNSAFE-NEXT: ret
 ; FINITE:      ogt_x:
-; FINITE-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; FINITE-NEXT: maxsd LCP{{.*}}(%rip), %xmm0
-; FINITE-NEXT: maxsd %xmm1, %xmm0
 ; FINITE-NEXT: ret
 define double @ogt_x(double %x) nounwind {
   %c = fcmp ogt double %x, 0.000000e+00
@@ -155,16 +152,13 @@ define double @ogt_x(double %x) nounwind {
 }
 
 ; CHECK:      olt_x:
-; CHECK-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; CHECK-NEXT: minsd LCP{{.*}}(%rip), %xmm0
-; CHECK-NEXT: minsd %xmm1, %xmm0
 ; CHECK-NEXT: ret
 ; UNSAFE:      olt_x:
-; UNSAFE-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; UNSAFE-NEXT: minsd LCP{{.*}}(%rip), %xmm0
-; UNSAFE-NEXT: minsd %xmm1, %xmm0
 ; UNSAFE-NEXT: ret
 ; FINITE:      olt_x:
-; FINITE-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; FINITE-NEXT: minsd LCP{{.*}}(%rip), %xmm0
-; FINITE-NEXT: minsd %xmm1, %xmm0
 ; FINITE-NEXT: ret
 define double @olt_x(double %x) nounwind {
   %c = fcmp olt double %x, 0.000000e+00
@@ -217,12 +211,10 @@ define double @olt_inverse_x(double %x) nounwind {
 ; CHECK:      oge_x:
 ; CHECK:      ucomisd %xmm1, %xmm0
 ; UNSAFE:      oge_x:
-; UNSAFE-NEXT: xorp{{[sd]}}   %xmm1, %xmm1
+; UNSAFE-NEXT: maxsd   LCP{{.*}}(%rip), %xmm0
-; UNSAFE-NEXT: maxsd   %xmm1, %xmm0
 ; UNSAFE-NEXT: ret
 ; FINITE:      oge_x:
-; FINITE-NEXT: xorp{{[sd]}}   %xmm1, %xmm1
+; FINITE-NEXT: maxsd   LCP{{.*}}(%rip), %xmm0
-; FINITE-NEXT: maxsd   %xmm1, %xmm0
 ; FINITE-NEXT: ret
 define double @oge_x(double %x) nounwind {
   %c = fcmp oge double %x, 0.000000e+00
@@ -233,12 +225,10 @@ define double @oge_x(double %x) nounwind {
 ; CHECK:      ole_x:
 ; CHECK:      ucomisd %xmm0, %xmm1
 ; UNSAFE:      ole_x:
-; UNSAFE-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; UNSAFE-NEXT: minsd LCP{{.*}}(%rip), %xmm0
-; UNSAFE-NEXT: minsd %xmm1, %xmm0
 ; UNSAFE-NEXT: ret
 ; FINITE:      ole_x:
-; FINITE-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; FINITE-NEXT: minsd LCP{{.*}}(%rip), %xmm0
-; FINITE-NEXT: minsd %xmm1, %xmm0
 ; FINITE-NEXT: ret
 define double @ole_x(double %x) nounwind {
   %c = fcmp ole double %x, 0.000000e+00
@@ -411,12 +401,10 @@ define double @ule_inverse(double %x, double %y) nounwind {
 ; CHECK:      ugt_x:
 ; CHECK:      ucomisd %xmm0, %xmm1
 ; UNSAFE:      ugt_x:
-; UNSAFE-NEXT: xorp{{[sd]}}   %xmm1, %xmm1
+; UNSAFE-NEXT: maxsd   LCP{{.*}}(%rip), %xmm0
-; UNSAFE-NEXT: maxsd   %xmm1, %xmm0
 ; UNSAFE-NEXT: ret
 ; FINITE:      ugt_x:
-; FINITE-NEXT: xorp{{[sd]}}   %xmm1, %xmm1
+; FINITE-NEXT: maxsd   LCP{{.*}}(%rip), %xmm0
-; FINITE-NEXT: maxsd   %xmm1, %xmm0
 ; FINITE-NEXT: ret
 define double @ugt_x(double %x) nounwind {
   %c = fcmp ugt double %x, 0.000000e+00
@@ -427,12 +415,10 @@ define double @ugt_x(double %x) nounwind {
 ; CHECK:      ult_x:
 ; CHECK:      ucomisd %xmm1, %xmm0
 ; UNSAFE:      ult_x:
-; UNSAFE-NEXT: xorp{{[sd]}}   %xmm1, %xmm1
+; UNSAFE-NEXT: minsd   LCP{{.*}}(%rip), %xmm0
-; UNSAFE-NEXT: minsd   %xmm1, %xmm0
 ; UNSAFE-NEXT: ret
 ; FINITE:      ult_x:
-; FINITE-NEXT: xorp{{[sd]}}   %xmm1, %xmm1
+; FINITE-NEXT: minsd   LCP{{.*}}(%rip), %xmm0
-; FINITE-NEXT: minsd   %xmm1, %xmm0
 ; FINITE-NEXT: ret
 define double @ult_x(double %x) nounwind {
   %c = fcmp ult double %x, 0.000000e+00
@@ -482,12 +468,10 @@ define double @ult_inverse_x(double %x) nounwind {
 ; CHECK-NEXT: movap{{[sd]}} %xmm1, %xmm0
 ; CHECK-NEXT: ret
 ; UNSAFE:      uge_x:
-; UNSAFE-NEXT: xorp{{[sd]}}  %xmm1, %xmm1
+; UNSAFE-NEXT: maxsd  LCP{{.*}}(%rip), %xmm0
-; UNSAFE-NEXT: maxsd  %xmm1, %xmm0
 ; UNSAFE-NEXT: ret
 ; FINITE:      uge_x:
-; FINITE-NEXT: xorp{{[sd]}}  %xmm1, %xmm1
+; FINITE-NEXT: maxsd  LCP{{.*}}(%rip), %xmm0
-; FINITE-NEXT: maxsd  %xmm1, %xmm0
 ; FINITE-NEXT: ret
 define double @uge_x(double %x) nounwind {
   %c = fcmp uge double %x, 0.000000e+00
@@ -501,12 +485,10 @@ define double @uge_x(double %x) nounwind {
 ; CHECK-NEXT: movap{{[sd]}} %xmm1, %xmm0
 ; CHECK-NEXT: ret
 ; UNSAFE:      ule_x:
-; UNSAFE-NEXT: xorp{{[sd]}}  %xmm1, %xmm1
+; UNSAFE-NEXT: minsd  LCP{{.*}}(%rip), %xmm0
-; UNSAFE-NEXT: minsd  %xmm1, %xmm0
 ; UNSAFE-NEXT: ret
 ; FINITE:      ule_x:
-; FINITE-NEXT: xorp{{[sd]}}  %xmm1, %xmm1
+; FINITE-NEXT: minsd  LCP{{.*}}(%rip), %xmm0
-; FINITE-NEXT: minsd  %xmm1, %xmm0
 ; FINITE-NEXT: ret
 define double @ule_x(double %x) nounwind {
   %c = fcmp ule double %x, 0.000000e+00
@@ -515,8 +497,7 @@ define double @ule_x(double %x) nounwind {
 }
 
 ; CHECK:      uge_inverse_x:
-; CHECK-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; CHECK-NEXT: minsd LCP{{.*}}(%rip), %xmm0
-; CHECK-NEXT: minsd %xmm1, %xmm0
 ; CHECK-NEXT: ret
 ; UNSAFE:      uge_inverse_x:
 ; UNSAFE-NEXT: xorp{{[sd]}} %xmm1, %xmm1
@@ -535,8 +516,7 @@ define double @uge_inverse_x(double %x) nounwind {
 }
 
 ; CHECK:      ule_inverse_x:
-; CHECK-NEXT: xorp{{[sd]}} %xmm1, %xmm1
+; CHECK-NEXT: maxsd LCP{{.*}}(%rip), %xmm0
-; CHECK-NEXT: maxsd %xmm1, %xmm0
 ; CHECK-NEXT: ret
 ; UNSAFE:      ule_inverse_x:
 ; UNSAFE-NEXT: xorp{{[sd]}} %xmm1, %xmm1

test/CodeGen/X86/vec_compare.ll

@@ -14,8 +14,8 @@ define <4 x i32> @test1(<4 x i32> %A, <4 x i32> %B) nounwind {
 define <4 x i32> @test2(<4 x i32> %A, <4 x i32> %B) nounwind {
 ; CHECK: test2:
 ; CHECK: pcmp
-; CHECK: pcmp
+; CHECK: pxor LCP
-; CHECK: pxor
+; CHECK: movdqa
 ; CHECK: ret
 	%C = icmp sge <4 x i32> %A, %B
         %D = sext <4 x i1> %C to <4 x i32>