Allow MachineCSE to coalesce trivial subregister copies the same way that it coalesces normal copies.

Without this, MachineCSE is powerless to handle redundant operations with truncated source operands.

This required fixing the 2-addr pass to handle tied subregisters. It isn't clear what combinations of subregisters can legally be tied, but the simple case of truncated source operands is now safely handled:

     %vreg11<def> = COPY %vreg1:sub_32bit; GR32:%vreg11 GR64:%vreg1
     %vreg12<def> = COPY %vreg2:sub_32bit; GR32:%vreg12 GR64:%vreg2
     %vreg13<def,tied1> = ADD32rr %vreg11<tied0>, %vreg12<kill>, %EFLAGS<imp-def>

Test case: cse-add-with-overflow.ll.

This exposed an existing bug in
PPCInstrInfo::commuteInstruction. Thanks to Rafael for the test case:
PowerPC/crash.ll.

llvm-svn: 197465

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
index af0bdedf17f..2bbaf4626b0 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -227,6 +227,8 @@ PPCInstrInfo::commuteInstruction(MachineInstr *MI, bool NewMI) const {
   unsigned Reg0 = MI->getOperand(0).getReg();
   unsigned Reg1 = MI->getOperand(1).getReg();
   unsigned Reg2 = MI->getOperand(2).getReg();
+  unsigned SubReg1 = MI->getOperand(1).getSubReg();
+  unsigned SubReg2 = MI->getOperand(2).getSubReg();
   bool Reg1IsKill = MI->getOperand(1).isKill();
   bool Reg2IsKill = MI->getOperand(2).isKill();
   bool ChangeReg0 = false;
@@ -236,6 +238,7 @@ PPCInstrInfo::commuteInstruction(MachineInstr *MI, bool NewMI) const {
     // Must be two address instruction!
     assert(MI->getDesc().getOperandConstraint(0, MCOI::TIED_TO) &&
            "Expecting a two-address instruction!");
+    assert(MI->getOperand(0).getSubReg() == SubReg1 && "Tied subreg mismatch");
     Reg2IsKill = false;
     ChangeReg0 = true;
   }
@@ -256,10 +259,14 @@ PPCInstrInfo::commuteInstruction(MachineInstr *MI, bool NewMI) const {
       .addImm((MB-1) & 31);
   }
 
-  if (ChangeReg0)
+  if (ChangeReg0) {
     MI->getOperand(0).setReg(Reg2);
+    MI->getOperand(0).setSubReg(SubReg2);
+  }
   MI->getOperand(2).setReg(Reg1);
   MI->getOperand(1).setReg(Reg2);
+  MI->getOperand(2).setSubReg(SubReg1);
+  MI->getOperand(1).setSubReg(SubReg2);
   MI->getOperand(2).setIsKill(Reg1IsKill);
   MI->getOperand(1).setIsKill(Reg2IsKill);
 
@@ -1591,4 +1598,3 @@ INITIALIZE_PASS(PPCEarlyReturn, DEBUG_TYPE,
 char PPCEarlyReturn::ID = 0;
 FunctionPass*
 llvm::createPPCEarlyReturnPass() { return new PPCEarlyReturn(); }
-