Fix R0 use in PowerPC VSX store for FastIsel.

The VSX stores are sometimes generated with a undefined index register, causing %noreg to be used and R0 to be emitted later on. The semantics of the VSX store (e.g. stdsdx) requires R0 to be used as base if we want zero to be used in the computation of the effective address instead of the content of R0. This patch checks if no index register was generated and forces R0 to be used as base address.

llvm-svn: 232486

1 files changed, 12 insertions, 2 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCFastISel.cpp b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
index 9dd9baa..fbd7b6d 100644
--- a/llvm/lib/Target/PowerPC/PPCFastISel.cpp
+++ b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
@@ -675,8 +675,18 @@ bool PPCFastISel::PPCEmitStore(MVT VT, unsigned SrcReg, Address &Addr) {
       case PPC::STFS: Opc = PPC::STFSX; break;
       case PPC::STFD: Opc = IsVSFRC ? PPC::STXSDX : PPC::STFDX; break;
     }
-    BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(Opc))
-      .addReg(SrcReg).addReg(Addr.Base.Reg).addReg(IndexReg);
+
+    auto MIB = BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(Opc))
+        .addReg(SrcReg);
+
+    // If we have an index register defined we use it in the store inst,
+    // otherwise we use X0 as base as it makes the vector instructions to
+    // use zero in the computation of the effective address regardless the
+    // content of the register.
+    if (IndexReg)
+      MIB.addReg(Addr.Base.Reg).addReg(IndexReg);
+    else
+      MIB.addReg(PPC::ZERO8).addReg(Addr.Base.Reg);
   }
 
   return true;