Revert "Enhance peephole optimization."

This reverts commit d84ca05.

Will revert, update commit message and re-commit.

Author: mingmingl-llvm

llvm/lib/Target/X86/X86InstrInfo.cpp

@@ -25,16 +25,13 @@
 #include "llvm/CodeGen/MachineConstantPool.h"
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
-#include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
-#include "llvm/CodeGen/MachineOperand.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/StackMaps.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
-#include "llvm/IR/InstrTypes.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
@@ -967,101 +964,6 @@ inline static bool isTruncatedShiftCountForLEA(unsigned ShAmt) {
   return ShAmt < 4 && ShAmt > 0;
 }
 
-static bool findRedundantFlagInstr(MachineInstr &CmpInstr,
-                                   MachineInstr &CmpValDefInstr,
-                                   const MachineRegisterInfo *MRI,
-                                   MachineInstr **AndInstr,
-                                   const TargetRegisterInfo *TRI,
-                                   bool &NoSignFlag, bool &ClearsOverflowFlag) {
-  if (CmpValDefInstr.getOpcode() != X86::SUBREG_TO_REG)
-    return false;
-
-  if (CmpInstr.getOpcode() != X86::TEST64rr)
-    return false;
-
-  // CmpInstr is a TEST64rr instruction, and `X86InstrInfo::analyzeCompare`
-  // guarantees that it's analyzable only if two registers are identical.
-  assert(
-      (CmpInstr.getOperand(0).getReg() == CmpInstr.getOperand(1).getReg()) &&
-      "CmpInstr is an analyzable TEST64rr, and `X86InstrInfo::analyzeCompare` "
-      "requires two reg operands are the same.");
-
-  // Caller (`X86InstrInfo::optimizeCompareInstr`) guarantees that
-  // `CmpValDefInstr` defines the value that's used by `CmpInstr`; in this case
-  // if `CmpValDefInstr` sets the EFLAGS, it is likely that `CmpInstr` is
-  // redundant.
-  assert(
-      (MRI->getVRegDef(CmpInstr.getOperand(0).getReg()) == &CmpValDefInstr) &&
-      "Caller guarantees that TEST64rr is a user of SUBREG_TO_REG.");
-
-  // As seen in X86 td files, CmpValDefInstr.getOperand(1).getImm() is typically
-  // 0.
-  if (CmpValDefInstr.getOperand(1).getImm() != 0)
-    return false;
-
-  // As seen in X86 td files, CmpValDefInstr.getOperand(3) is typically
-  // sub_32bit or sub_xmm.
-  if (CmpValDefInstr.getOperand(3).getImm() != X86::sub_32bit)
-    return false;
-
-  MachineInstr *VregDefInstr =
-      MRI->getVRegDef(CmpValDefInstr.getOperand(2).getReg());
-
-  assert(VregDefInstr && "Must have a definition (SSA)");
-
-  // Requires `CmpValDefInstr` and `VregDefInstr` are from the same MBB
-  // to simplify the subsequent analysis.
-  //
-  // FIXME: If `VregDefInstr->getParent()` is the only predecessor of
-  // `CmpValDefInstr.getParent()`, this could be handled.
-  if (VregDefInstr->getParent() != CmpValDefInstr.getParent())
-    return false;
-
-  if (X86::isAND(VregDefInstr->getOpcode())) {
-    // Get a sequence of instructions like
-    //   %reg = and* ...                    // Set EFLAGS
-    //   ...                                // EFLAGS not changed
-    //   %extended_reg = subreg_to_reg 0, %reg, %subreg.sub_32bit
-    //   test64rr %extended_reg, %extended_reg, implicit-def $eflags
-    //
-    // If subsequent readers use a subset of bits that don't change
-    // after `and*` instructions, it's likely that the test64rr could
-    // be optimized away.
-    for (const MachineInstr &Instr :
-         make_range(std::next(MachineBasicBlock::iterator(VregDefInstr)),
-                    MachineBasicBlock::iterator(CmpValDefInstr))) {
-      // There are instructions between 'VregDefInstr' and
-      // 'CmpValDefInstr' that modifies EFLAGS.
-      if (Instr.modifiesRegister(X86::EFLAGS, TRI))
-        return false;
-    }
-
-    *AndInstr = VregDefInstr;
-
-    // AND instruction will essentially update SF and clear OF, so
-    // NoSignFlag should be false in the sense that SF is modified by `AND`.
-    //
-    // However, the implementation artifically sets `NoSignFlag` to true
-    // to poison the SF bit; that is to say, if SF is looked at later, the
-    // optimization (to erase TEST64rr) will be disabled.
-    //
-    // The reason to poison SF bit is that SF bit value could be different
-    // in the `AND` and `TEST` operation; signed bit is not known for `AND`,
-    // and is known to be 0 as a result of `TEST64rr`.
-    //
-    // FIXME: As opposed to poisoning the SF bit direclty, consider peeking into
-    // the AND instruction and using the static information to guide peephole optimization if possible.
-    // For example, it's possible to fold a conditional move into a copy
-    // if the relevant EFLAG bits could be deduced from an immediate operand of and operation.
-    // 
-    NoSignFlag = true;
-    // ClearsOverflowFlag is true for AND operation (no surprise).
-    ClearsOverflowFlag = true;
-    return true;
-  }
-  return false;
-}
-
 bool X86InstrInfo::classifyLEAReg(MachineInstr &MI, const MachineOperand &Src,
                                   unsigned Opc, bool AllowSP, Register &NewSrc,
                                   bool &isKill, MachineOperand &ImplicitOp,
@@ -4324,23 +4226,6 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
           MI = &Inst;
           break;
         }
-
-        // Look back for the following pattern, in which case the test64rr
-        // instruction could be erased.
-        //
-        // Example:
-        //  %reg = and32ri %in_reg, 5
-        //  ...                         // EFLAGS not changed.
-        //  %src_reg = subreg_to_reg 0, %reg, %subreg.sub_index
-        //  test64rr %src_reg, %src_reg, implicit-def $eflags
-        MachineInstr *AndInstr = nullptr;
-        if (IsCmpZero &&
-            findRedundantFlagInstr(CmpInstr, Inst, MRI, &AndInstr, TRI,
-                                   NoSignFlag, ClearsOverflowFlag)) {
-          assert(AndInstr != nullptr && X86::isAND(AndInstr->getOpcode()));
-          MI = AndInstr;
-          break;
-        }
         // Cannot find other candidates before definition of SrcReg.
         return false;
       }