[llvm-commits] [llvm] r98599 - /llvm/trunk/lib/CodeGen/RegAllocLocal.cpp

[Evan Cheng]

On Mar 15, 2010, at 6:05 PM, Bill Wendling wrote:

> Author: void
> Date: Mon Mar 15 20:05:35 2010
> New Revision: 98599
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=98599&view=rev
> Log:
> When checking if something's killed, don't rely simply on whether it's marked as
> "used outside of the block". If the block ends in a return, then it won't be
> used outside of it.
> 
> Modified:
>    llvm/trunk/lib/CodeGen/RegAllocLocal.cpp
> 
> Modified: llvm/trunk/lib/CodeGen/RegAllocLocal.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegAllocLocal.cpp?rev=98599&r1=98598&r2=98599&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/RegAllocLocal.cpp (original)
> +++ llvm/trunk/lib/CodeGen/RegAllocLocal.cpp Mon Mar 15 20:05:35 2010
> @@ -671,7 +671,8 @@
> 
>   // Live-out (of the function) registers contain return values of the function,
>   // so we need to make sure they are alive at return time.
> -  if (!MBB.empty() && MBB.back().getDesc().isReturn()) {
> +  bool BBEndsInReturn = !MBB.empty() && MBB.back().getDesc().isReturn();

I think it should use getFirstTerminator() instead.

Evan

> +  if (BBEndsInReturn) {
>     MachineInstr* Ret = &MBB.back();
>     for (MachineRegisterInfo::liveout_iterator
>          I = MF->getRegInfo().liveout_begin(),
> @@ -696,7 +697,10 @@
>     bool usedOutsideBlock = isPhysReg ? false :   
>           UsedInMultipleBlocks.test(MO.getReg() -  
>                                     TargetRegisterInfo::FirstVirtualRegister);
> -    if (!isPhysReg && !usedOutsideBlock) {
> +
> +    // If the machine BB ends in a return instruction, then the value isn't used
> +    // outside of the BB.
> +    if (!isPhysReg && (!usedOutsideBlock || BBEndsInReturn)) {
>       // DBG_VALUE complicates this:  if the only refs of a register outside
>       // this block are DBG_VALUE, we can't keep the reg live just for that,
>       // as it will cause the reg to be spilled at the end of this block when
> @@ -704,7 +708,7 @@
>       // happens.
>       bool UsedByDebugValueOnly = false;
>       for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()),
> -           UE = MRI.reg_end(); UI != UE; ++UI)
> +             UE = MRI.reg_end(); UI != UE; ++UI) {
>         // Two cases:
>         // - used in another block
>         // - used in the same block before it is defined (loop)
> @@ -714,6 +718,7 @@
>             UsedByDebugValueOnly = true;
>             continue;
>           }
> +
>           // A non-DBG_VALUE use means we can leave DBG_VALUE uses alone.
>           UsedInMultipleBlocks.set(MO.getReg() - 
>                                    TargetRegisterInfo::FirstVirtualRegister);
> @@ -721,6 +726,8 @@
>           UsedByDebugValueOnly = false;
>           break;
>         }
> +      }
> +
>       if (UsedByDebugValueOnly)
>         for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()),
>              UE = MRI.reg_end(); UI != UE; ++UI)
> @@ -730,16 +737,16 @@
>             UI.getOperand().setReg(0U);
>     }
> 
> -    // Physical registers and those that are not live-out of the block
> -    // are killed/dead at their last use/def within this block.
> -    if (isPhysReg || !usedOutsideBlock) {
> +    // Physical registers and those that are not live-out of the block are
> +    // killed/dead at their last use/def within this block.
> +    if (isPhysReg || !usedOutsideBlock || BBEndsInReturn)
>       if (MO.isUse()) {
>         // Don't mark uses that are tied to defs as kills.
>         if (!MI->isRegTiedToDefOperand(idx))
>           MO.setIsKill(true);
> -      } else
> +      } else {
>         MO.setIsDead(true);
> -    }
> +      }
>   }
> }
> 
> 
> 
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