Merge information about the number of zero, one, and sign bits of live-out registers

at phis. This enables us to eliminate a lot of pointless zexts during the DAGCombine
phase. This fixes <rdar://problem/8760114>.

llvm-svn: 126170

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 452f5614b7b..c1be3e95fc4 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -644,7 +644,10 @@ SDValue RegsForValue::getCopyFromRegs(SelectionDAG &DAG,
           !RegisterVT.isInteger() || RegisterVT.isVector() ||
           !FuncInfo.LiveOutRegInfo.inBounds(Regs[Part+i]))
         continue;
-      
+
+      if (FuncInfo.PHIDestRegs.count(Regs[Part+i]) && !FuncInfo.AllPredsVisited)
+        continue;
+
       const FunctionLoweringInfo::LiveOutInfo &LOI =
         FuncInfo.LiveOutRegInfo[Regs[Part+i]];
 
@@ -6466,6 +6469,9 @@ SelectionDAGBuilder::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
         }
       }
 
+      if (!EnableFastISel)
+        FuncInfo.PHISrcToDestMap[Reg] = FuncInfo.ValueMap[PN];
+
       // Remember that this register needs to added to the machine PHI node as
       // the input for this MBB.
       SmallVector<EVT, 4> ValueVTs;