MachineInstr: Respect register aliases in clearRegiserKills()

[MatzeB]

Summary

This fixes bugs in copy elimination code in llvm. It slightly changes the
semantics of clearRegisterKills(). This is appropriate because:

• Users in lib/CodeGen/MachineCopyPropagation.cpp and lib/Target/AArch64RedundantCopyElimination.cpp and lib/Target/SystemZ/SystemZElimCompare.cpp are incorrect without it (see included testcase).
• All other users in llvm are unaffected (they pass TRI==nullptr)
• Kill flags are optional anyway.

[qcolombet]

Hi Matthias,

LGTM.

Thanks,
Q.

test/CodeGen/X86/machine-copy-prop.mir

10 ↗

(On Diff #48854)

Typo -> redundant.

[mcrosier]

llvm/trunk/lib/CodeGen/MachineInstr.cpp

1970

As a compile-time optimization, would it make sense to perform the Reg == OpReg check before making the call to regsOverlap?

llvm/trunk/include/llvm/CodeGen/MachineInstr.h

#endif
   /// We have determined MI kills a register. Look for the
   /// operand that uses it and mark it as IsKill. If AddIfNotFound is true,
   /// add a implicit operand if it's not found. Returns true if the operand
   /// exists / is added.
   bool addRegisterKilled(unsigned IncomingReg,
                          const TargetRegisterInfo *RegInfo,
                          bool AddIfNotFound = false);
 
-  /// Clear all kill flags affecting Reg.  If RegInfo is
-  /// provided, this includes super-register kills.
+  /// Clear all kill flags affecting Reg.  If RegInfo is provided, this includes
+  /// all aliasing registers.
   void clearRegisterKills(unsigned Reg, const TargetRegisterInfo *RegInfo);
 
   /// We have determined MI defined a register without a use.
   /// Look for the operand that defines it and mark it as IsDead. If
   /// AddIfNotFound is true, add a implicit operand if it's not found. Returns
   /// true if the operand exists / is added.
   bool addRegisterDead(unsigned Reg, const TargetRegisterInfo *RegInfo,
                        bool AddIfNotFound = false);

llvm/trunk/lib/CodeGen/MachineInstr.cpp

 void MachineInstr::clearRegisterKills(unsigned Reg,
                                       const TargetRegisterInfo *RegInfo) {
   if (!TargetRegisterInfo::isPhysicalRegister(Reg))
     RegInfo = nullptr;
   for (MachineOperand &MO : operands()) {
     if (!MO.isReg() || !MO.isUse() || !MO.isKill())
       continue;
     unsigned OpReg = MO.getReg();
-    if (OpReg == Reg || (RegInfo && RegInfo->isSuperRegister(Reg, OpReg)))
+    if ((RegInfo && RegInfo->regsOverlap(Reg, OpReg)) || Reg == OpReg)
       MO.setIsKill(false);
   }
 }
 
 bool MachineInstr::addRegisterDead(unsigned Reg,
                                    const TargetRegisterInfo *RegInfo,
                                    bool AddIfNotFound) {
   bool isPhysReg = TargetRegisterInfo::isPhysicalRegister(Reg);

llvm/trunk/test/CodeGen/X86/machine-copy-prop.mir

+# RUN: llc -march=x86 -run-pass machine-cp -verify-machineinstrs -o /dev/null %s 2>&1 | FileCheck %s
+
+--- |
+  declare void @foo()
+  define void @copyprop_remove_kill0() { ret void }
+  define void @copyprop_remove_kill1() { ret void }
+  define void @copyprop_remove_kill2() { ret void }
+...
+---
+# The second copy is redundand and will be removed, check that we also remove
+# the kill flag of intermediate instructions.
+# CHECK-LABEL: name: copyprop_remove_kill0
+# CHECK: bb.0:
+# CHECK-NEXT: %rax = COPY %rdi
+# CHECK-NEXT: NOOP implicit %rdi
+# CHECK-NOT: COPY
+# CHECK-NEXT: NOOP implicit %rax, implicit %rdi
+name: copyprop_remove_kill0
+body: |
+  bb.0:
+    %rax = COPY %rdi
+    NOOP implicit killed %rdi
+    %rdi = COPY %rax
+    NOOP implicit %rax, implicit %rdi
+...
+---
+# The second copy is redundand and will be removed, check that we also remove
+# the kill flag of intermediate instructions.
+# CHECK-LABEL: name: copyprop_remove_kill1
+# CHECK: bb.0:
+# CHECK-NEXT: %rax = COPY %rdi
+# CHECK-NEXT: NOOP implicit %edi
+# CHECK-NOT: COPY
+# CHECK-NEXT: NOOP implicit %rax, implicit %rdi
+name: copyprop_remove_kill1
+body: |
+  bb.0:
+    %rax = COPY %rdi
+    NOOP implicit killed %edi
+    %rdi = COPY %rax
+    NOOP implicit %rax, implicit %rdi
+...
+---
+# The second copy is redundand and will be removed, check that we also remove
+# the kill flag of intermediate instructions.
+# CHECK-LABEL: name: copyprop_remove_kill2
+# CHECK: bb.0:
+# CHECK-NEXT: %ax = COPY %di
+# CHECK-NEXT: NOOP implicit %rdi
+# CHECK-NOT: COPY
+# CHECK-NEXT: NOOP implicit %rax, implicit %rdi
+name: copyprop_remove_kill2
+body: |
+  bb.0:
+    %ax = COPY %di
+    NOOP implicit killed %rdi
+    %di = COPY %ax
+    NOOP implicit %rax, implicit %rdi
+...