[CodeGen] Fix dependence breaking for tied operands

Differential Revision: https://reviews.llvm.org/D107582

llvm/lib/CodeGen/CriticalAntiDepBreaker.cpp

@@ -212,6 +212,21 @@ void CriticalAntiDepBreaker::PrescanInstruction(MachineInstr &MI) {
     if (Classes[Reg] != reinterpret_cast<TargetRegisterClass *>(-1))
       RegRefs.insert(std::make_pair(Reg, &MO));
 
+    if (MO.isUse() && Special) {
+      if (!KeepRegs.test(Reg)) {
+        for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
+             SubRegs.isValid(); ++SubRegs)
+          KeepRegs.set(*SubRegs);
+      }
+    }
+  }
+
+  for (unsigned I = 0, E = MI.getNumOperands(); I != E; ++I) {
+    const MachineOperand &MO = MI.getOperand(I);
+    if (!MO.isReg()) continue;
+    Register Reg = MO.getReg();
+    if (!Reg.isValid())
+      continue;
     // If this reg is tied and live (Classes[Reg] is set to -1), we can't change
     // it or any of its sub or super regs. We need to use KeepRegs to mark the
     // reg because not all uses of the same reg within an instruction are
@@ -222,7 +237,7 @@ void CriticalAntiDepBreaker::PrescanInstruction(MachineInstr &MI) {
     // of a register? In the above 'xor' example, the uses of %eax are undef, so
     // earlier instructions could still replace %eax even though the 'xor'
     // itself can't be changed.
-    if (MI.isRegTiedToUseOperand(i) &&
+    if (MI.isRegTiedToUseOperand(I) &&
         Classes[Reg] == reinterpret_cast<TargetRegisterClass *>(-1)) {
       for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
            SubRegs.isValid(); ++SubRegs) {
@@ -233,14 +248,6 @@ void CriticalAntiDepBreaker::PrescanInstruction(MachineInstr &MI) {
         KeepRegs.set(*SuperRegs);
       }
     }
-
-    if (MO.isUse() && Special) {
-      if (!KeepRegs.test(Reg)) {
-        for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
-             SubRegs.isValid(); ++SubRegs)
-          KeepRegs.set(*SubRegs);
-      }
-    }
   }
 }
 

llvm/test/CodeGen/X86/tied-depbreak.mir

@@ -0,0 +1,64 @@
+# RUN: llc -mtriple=x86_64-unknown-linux-gnu -mcpu=slm -run-pass post-RA-sched -o - %s | FileCheck %s
+#
+# Verify that the critical antidependence breaker does not partially
+# replace tied operands
+
+--- |
+
+  define void @main() { ret void }
+
+...
+---
+# CHECK-LABEL: main
+name:            main
+alignment:       16
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:
+  - { reg: '$edi', virtual-reg: '' }
+  - { reg: '$esi', virtual-reg: '' }
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       0
+  offsetAdjustment: 0
+  maxAlignment:    1
+  adjustsStack:    false
+  hasCalls:        false
+  stackProtector:  ''
+  maxCallFrameSize: 0
+  cvBytesOfCalleeSavedRegisters: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  localFrameSize:  0
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:      []
+stack:           []
+callSites:       []
+debugValueSubstitutions: []
+constants:       []
+machineFunctionInfo: {}
+body:             |
+  bb.0:
+    liveins: $edi, $esi
+
+    $eax = MOV32rr $esi
+    $eax = LEA64_32r $rdi, 1, $rsi, 0, $noreg
+    $edi = MOV32rr $esi
+    $esi = MOV32ri 4
+    ; Verify that XOR is untouched by the dependency breaker
+    ; CHECK: $esi = XOR32rr undef $esi, undef $esi, implicit-def dead $eflags, implicit-def $rsi
+    $esi = XOR32rr undef $esi, undef $esi, implicit-def dead $eflags, implicit-def $rsi
+    RETQ killed $eax
+
+...