[X86][CodeGen] Support flags copy lowering for CCMP/CTEST (llvm#91849)

```
%1:gr64 = COPY $eflags
OP1 may update eflags
$eflags = COPY %1
OP2 may use eflags
```

To use eflags as input at 4th instruction, we need to use SETcc to
preserve the eflags before 2, and update the source condition of OP2
according to value in GPR %1.

In this patch, we support CCMP/CTEST as OP2.

Author: KanRobert

llvm/lib/Target/X86/X86FlagsCopyLowering.cpp

@@ -124,6 +124,10 @@ class X86FlagsCopyLoweringPass : public MachineFunctionPass {
                     MachineBasicBlock::iterator TestPos,
                     const DebugLoc &TestLoc, MachineInstr &SetCCI,
                     MachineOperand &FlagUse, CondRegArray &CondRegs);
+  void rewriteCCMP(MachineBasicBlock &TestMBB,
+                   MachineBasicBlock::iterator TestPos, const DebugLoc &TestLoc,
+                   MachineInstr &CMovI, MachineOperand &FlagUse,
+                   CondRegArray &CondRegs);
 };
 
 } // end anonymous namespace
@@ -613,6 +617,9 @@ bool X86FlagsCopyLoweringPass::runOnMachineFunction(MachineFunction &MF) {
           rewriteFCMov(*TestMBB, TestPos, TestLoc, MI, *FlagUse, CondRegs);
         } else if (X86::getCondFromSETCC(MI) != X86::COND_INVALID) {
           rewriteSetCC(*TestMBB, TestPos, TestLoc, MI, *FlagUse, CondRegs);
+        } else if (X86::getCondFromCCMP(MI) != X86::COND_INVALID) {
+          rewriteCCMP(*TestMBB, TestPos, TestLoc, MI, *FlagUse, CondRegs);
+          FlagsKilled = true;
         } else if (MI.getOpcode() == TargetOpcode::COPY) {
           rewriteCopy(MI, *FlagUse, CopyDefI);
         } else {
@@ -970,3 +977,29 @@ void X86FlagsCopyLoweringPass::rewriteSetCC(MachineBasicBlock &TestMBB,
 
   SetCCI.eraseFromParent();
 }
+
+void X86FlagsCopyLoweringPass::rewriteCCMP(MachineBasicBlock &TestMBB,
+                                           MachineBasicBlock::iterator TestPos,
+                                           const DebugLoc &TestLoc,
+                                           MachineInstr &CCMPI,
+                                           MachineOperand &FlagUse,
+                                           CondRegArray &CondRegs) {
+  // First get the register containing this specific condition.
+  X86::CondCode Cond = X86::getCondFromCCMP(CCMPI);
+  unsigned CondReg;
+  bool Inverted;
+  std::tie(CondReg, Inverted) =
+      getCondOrInverseInReg(TestMBB, TestPos, TestLoc, Cond, CondRegs);
+
+  MachineBasicBlock &MBB = *CCMPI.getParent();
+
+  // Insert a direct test of the saved register.
+  insertTest(MBB, CCMPI.getIterator(), CCMPI.getDebugLoc(), CondReg);
+
+  // Rewrite the CCMP/CTEST to use the !ZF flag from the test, and then kill its
+  // use of the flags afterward.
+  CCMPI.getOperand(CCMPI.getDesc().getNumOperands() - 1)
+      .setImm(Inverted ? X86::COND_E : X86::COND_NE);
+  FlagUse.setIsKill(true);
+  LLVM_DEBUG(dbgs() << "    fixed ccmp/ctest: "; CCMPI.dump());
+}

llvm/lib/Target/X86/X86InstrInfo.cpp

@@ -3121,7 +3121,8 @@ bool X86InstrInfo::hasCommutePreference(MachineInstr &MI, bool &Commute) const {
 int X86::getCondSrcNoFromDesc(const MCInstrDesc &MCID) {
   unsigned Opcode = MCID.getOpcode();
   if (!(X86::isJCC(Opcode) || X86::isSETCC(Opcode) || X86::isCMOVCC(Opcode) ||
-        X86::isCFCMOVCC(Opcode)))
+        X86::isCFCMOVCC(Opcode) || X86::isCCMPCC(Opcode) ||
+        X86::isCTESTCC(Opcode)))
     return -1;
   // Assume that condition code is always the last use operand.
   unsigned NumUses = MCID.getNumOperands() - MCID.getNumDefs();
@@ -3157,6 +3158,12 @@ X86::CondCode X86::getCondFromCFCMov(const MachineInstr &MI) {
                                          : X86::COND_INVALID;
 }
 
+X86::CondCode X86::getCondFromCCMP(const MachineInstr &MI) {
+  return X86::isCCMPCC(MI.getOpcode()) || X86::isCTESTCC(MI.getOpcode())
+             ? X86::getCondFromMI(MI)
+             : X86::COND_INVALID;
+}
+
 /// Return the inverse of the specified condition,
 /// e.g. turning COND_E to COND_NE.
 X86::CondCode X86::GetOppositeBranchCondition(X86::CondCode CC) {

llvm/lib/Target/X86/X86InstrInfo.h

@@ -71,6 +71,9 @@ CondCode getCondFromCMov(const MachineInstr &MI);
 // Turn CFCMOV instruction into condition code.
 CondCode getCondFromCFCMov(const MachineInstr &MI);
 
+// Turn CCMP instruction into condition code.
+CondCode getCondFromCCMP(const MachineInstr &MI);
+
 /// GetOppositeBranchCondition - Return the inverse of the specified cond,
 /// e.g. turning COND_E to COND_NE.
 CondCode GetOppositeBranchCondition(CondCode CC);

llvm/test/CodeGen/X86/apx/ccmp-flags-copy-lowering.mir

@@ -0,0 +1,51 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 4
+# RUN: llc -mtriple=x86_64 -run-pass x86-flags-copy-lowering -verify-machineinstrs -o - %s | FileCheck %s
+# Lower various interesting copy patterns of EFLAGS without using LAHF/SAHF.
+
+...
+---
+name:            test_ccmp
+body:             |
+  bb.0:
+    liveins: $edi
+
+    ; CHECK-LABEL: name: test_ccmp
+    ; CHECK: liveins: $edi
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: MUL32r $edi, implicit-def $eax, implicit-def dead $edx, implicit-def $eflags, implicit $eax
+    ; CHECK-NEXT: [[SETCCr:%[0-9]+]]:gr8 = SETCCr 1, implicit $eflags
+    ; CHECK-NEXT: [[ADD32rr:%[0-9]+]]:gr32 = ADD32rr $edi, $edi, implicit-def $eflags
+    ; CHECK-NEXT: TEST8rr [[SETCCr]], [[SETCCr]], implicit-def $eflags
+    ; CHECK-NEXT: CCMP32rr [[ADD32rr]], [[ADD32rr]], 0, 5, implicit-def $eflags, implicit killed $eflags
+    ; CHECK-NEXT: RET 0, $al
+    MUL32r $edi, implicit-def $eax, implicit-def dead $edx, implicit-def $eflags, implicit $eax
+    %1:gr64 = COPY $eflags
+    %2:gr32 = ADD32rr $edi, $edi, implicit-def $eflags
+    $eflags = COPY %1
+    CCMP32rr %2, %2, 0, 1, implicit-def $eflags, implicit $eflags
+    RET 0, $al
+
+...
+---
+name:            test_ctest
+body:             |
+  bb.0:
+    liveins: $edi
+
+    ; CHECK-LABEL: name: test_ctest
+    ; CHECK: liveins: $edi
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: MUL32r $edi, implicit-def $eax, implicit-def dead $edx, implicit-def $eflags, implicit $eax
+    ; CHECK-NEXT: [[SETCCr:%[0-9]+]]:gr8 = SETCCr 1, implicit $eflags
+    ; CHECK-NEXT: [[ADD32rr:%[0-9]+]]:gr32 = ADD32rr $edi, $edi, implicit-def $eflags
+    ; CHECK-NEXT: TEST8rr [[SETCCr]], [[SETCCr]], implicit-def $eflags
+    ; CHECK-NEXT: CTEST32rr [[ADD32rr]], [[ADD32rr]], 0, 5, implicit-def $eflags, implicit killed $eflags
+    ; CHECK-NEXT: RET 0, $al
+    MUL32r $edi, implicit-def $eax, implicit-def dead $edx, implicit-def $eflags, implicit $eax
+    %1:gr64 = COPY $eflags
+    %2:gr32 = ADD32rr $edi, $edi, implicit-def $eflags
+    $eflags = COPY %1
+    CTEST32rr %2, %2, 0, 1, implicit-def $eflags, implicit $eflags
+    RET 0, $al
+
+...