[llvm] r204976 - [PowerPC] Don't remove self VSX copies in PPCInstrInfo::copyPhysReg

[Hal Finkel]

Author: hfinkel
Date: Thu Mar 27 17:46:28 2014
New Revision: 204976

URL: http://llvm.org/viewvc/llvm-project?rev=204976&view=rev
Log:
[PowerPC] Don't remove self VSX copies in PPCInstrInfo::copyPhysReg

Because of how the allocation of VSX registers interacts with the call-lowering
code, we sometimes end up generating self VSX copies. Specifically, things like
this:
  %VSL2<def> = COPY %F2, %VSL2<imp-use,kill>
(where %F2 is really a sub-register of %VSL2, and so this copy is a nop)

The problem is that ExpandPostRAPseudos always assumes that *some* instruction
has been inserted, and adds implicit defs to it. This is a problem if no copy
was inserted because it can cause subtle problems during post-RA scheduling.
These self copies will have to be removed some other way.

Modified:
    llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp

Modified: llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp?rev=204976&r1=204975&r2=204976&view=diff
==============================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp Thu Mar 27 17:46:28 2014
@@ -51,6 +51,10 @@ cl::desc("Disable compare instruction op
 static cl::opt<bool> DisableVSXFMAMutate("disable-ppc-vsx-fma-mutation",
 cl::desc("Disable VSX FMA instruction mutation"), cl::Hidden);
 
+static cl::opt<bool> VSXSelfCopyCrash("crash-on-ppc-vsx-self-copy",
+cl::desc("Causes the backend to crash instead of generating a nop VSX copy"),
+cl::Hidden);
+
 // Pin the vtable to this file.
 void PPCInstrInfo::anchor() {}
 
@@ -679,15 +683,15 @@ void PPCInstrInfo::copyPhysReg(MachineBa
                                unsigned DestReg, unsigned SrcReg,
                                bool KillSrc) const {
   // We can end up with self copies and similar things as a result of VSX copy
-  // legalization. Promote (or just ignore) them here.
+  // legalization. Promote them here.
   const TargetRegisterInfo *TRI = &getRegisterInfo();
   if (PPC::F8RCRegClass.contains(DestReg) &&
       PPC::VSLRCRegClass.contains(SrcReg)) {
     unsigned SuperReg =
       TRI->getMatchingSuperReg(DestReg, PPC::sub_64, &PPC::VSRCRegClass);
 
-    if (SrcReg == SuperReg)
-      return;
+    if (VSXSelfCopyCrash && SrcReg == SuperReg)
+      llvm_unreachable("nop VSX copy");
 
     DestReg = SuperReg;
   } else if (PPC::VRRCRegClass.contains(DestReg) &&
@@ -695,8 +699,8 @@ void PPCInstrInfo::copyPhysReg(MachineBa
     unsigned SuperReg =
       TRI->getMatchingSuperReg(DestReg, PPC::sub_128, &PPC::VSRCRegClass);
 
-    if (SrcReg == SuperReg)
-      return;
+    if (VSXSelfCopyCrash && SrcReg == SuperReg)
+      llvm_unreachable("nop VSX copy");
 
     DestReg = SuperReg;
   } else if (PPC::F8RCRegClass.contains(SrcReg) &&
@@ -704,8 +708,8 @@ void PPCInstrInfo::copyPhysReg(MachineBa
     unsigned SuperReg =
       TRI->getMatchingSuperReg(SrcReg, PPC::sub_64, &PPC::VSRCRegClass);
 
-    if (DestReg == SuperReg)
-      return;
+    if (VSXSelfCopyCrash && DestReg == SuperReg)
+      llvm_unreachable("nop VSX copy");
 
     SrcReg = SuperReg;
   } else if (PPC::VRRCRegClass.contains(SrcReg) &&
@@ -713,8 +717,8 @@ void PPCInstrInfo::copyPhysReg(MachineBa
     unsigned SuperReg =
       TRI->getMatchingSuperReg(SrcReg, PPC::sub_128, &PPC::VSRCRegClass);
 
-    if (DestReg == SuperReg)
-      return;
+    if (VSXSelfCopyCrash && DestReg == SuperReg)
+      llvm_unreachable("nop VSX copy");
 
     SrcReg = SuperReg;
   }