[MachineCopyPropagation] BackwardPropagatableCopy: add check for hasOverlappingMultipleDef

In MachineCopyPropagation::BackwardPropagatableCopy(),
a check is added for multiple destination registers.

The copy propagation is avoided if the copied destination register
is the same register as another destination on the same instruction.

A new test is added.  This used to fail on ARM like this:
error: unpredictable instruction, RdHi and RdLo must be different
        umull   r9, r9, lr, r0

Reviewed By: lkail

Differential Revision: https://reviews.llvm.org/D82638

Author: simonwallis2

llvm/lib/CodeGen/MachineCopyPropagation.cpp

@@ -288,6 +288,8 @@ class MachineCopyPropagation : public MachineFunctionPass {
                                           const MachineInstr &UseI,
                                           unsigned UseIdx);
   bool hasImplicitOverlap(const MachineInstr &MI, const MachineOperand &Use);
+  bool hasOverlappingMultipleDef(const MachineInstr &MI,
+                                 const MachineOperand &MODef, Register Def);
 
   /// Candidates for deletion.
   SmallSetVector<MachineInstr *, 8> MaybeDeadCopies;
@@ -461,6 +463,21 @@ bool MachineCopyPropagation::hasImplicitOverlap(const MachineInstr &MI,
   return false;
 }
 
+/// For an MI that has multiple definitions, check whether \p MI has
+/// a definition that overlaps with another of its definitions.
+/// For example, on ARM: umull   r9, r9, lr, r0
+/// The umull instruction is unpredictable unless RdHi and RdLo are different.
+bool MachineCopyPropagation::hasOverlappingMultipleDef(
+    const MachineInstr &MI, const MachineOperand &MODef, Register Def) {
+  for (const MachineOperand &MIDef : MI.defs()) {
+    if ((&MIDef != &MODef) && MIDef.isReg() &&
+        TRI->regsOverlap(Def, MIDef.getReg()))
+      return true;
+  }
+
+  return false;
+}
+
 /// Look for available copies whose destination register is used by \p MI and
 /// replace the use in \p MI with the copy's source register.
 void MachineCopyPropagation::forwardUses(MachineInstr &MI) {
@@ -786,6 +803,9 @@ void MachineCopyPropagation::propagateDefs(MachineInstr &MI) {
     if (hasImplicitOverlap(MI, MODef))
       continue;
 
+    if (hasOverlappingMultipleDef(MI, MODef, Def))
+      continue;
+
     LLVM_DEBUG(dbgs() << "MCP: Replacing " << printReg(MODef.getReg(), TRI)
                       << "\n     with " << printReg(Def, TRI) << "\n     in "
                       << MI << "     from " << *Copy);

llvm/test/CodeGen/ARM/mcp-dest-regs-no-dup.mir

@@ -0,0 +1,13 @@
+# RUN: llc -mtriple=arm-eabi -O1 -run-pass=machine-cp %s -o - \
+# RUN: -verify-machineinstrs -simplify-mir | FileCheck %s
+
+name:            h
+body:             |
+  bb.0:
+
+    dead renamable $r9, renamable $r0 = UMULL renamable $lr, killed renamable $r0, 14 /* CC::al */, $noreg, $noreg
+
+  ; CHECK: dead renamable $r9, renamable $r0 = UMULL renamable $lr, killed renamable $r0, 14 /* CC::al */, $noreg, $noreg
+
+    renamable $r9 = COPY killed renamable $r0
+...