Don't copy the operand of a SwitchInst into virtual registers as

eagerly. This helps avoid CopyToReg nodes in some cases where they
aren't needed, and also helps subsequent optimizer heuristics
in cases where the extra nodes would cause the node to appear
to have multiple results. This doesn't have a significant impact
currently; it'll help an upcoming change.

llvm-svn: 68667

1 files changed, 13 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
index ba59906b6da..fd15603d990 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
@@ -243,9 +243,7 @@ static bool isUsedOutsideOfDefiningBlock(Instruction *I) {
   if (isa<PHINode>(I)) return true;
   BasicBlock *BB = I->getParent();
   for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; ++UI)
-    if (cast<Instruction>(*UI)->getParent() != BB || isa<PHINode>(*UI) ||
-        // FIXME: Remove switchinst special case.
-        isa<SwitchInst>(*UI))
+    if (cast<Instruction>(*UI)->getParent() != BB || isa<PHINode>(*UI))
       return true;
   return false;
 }
@@ -1640,6 +1638,9 @@ bool SelectionDAGLowering::handleSmallSwitchRange(CaseRec& CR,
     if (I != E-1) {
       FallThrough = CurMF->CreateMachineBasicBlock(CurBlock->getBasicBlock());
       CurMF->insert(BBI, FallThrough);
+
+      // Put SV in a virtual register to make it available from the new blocks.
+      ExportFromCurrentBlock(SV);
     } else {
       // If the last case doesn't match, go to the default block.
       FallThrough = Default;
@@ -1874,6 +1875,9 @@ bool SelectionDAGLowering::handleBTSplitSwitchCase(CaseRec& CR,
     TrueBB = CurMF->CreateMachineBasicBlock(LLVMBB);
     CurMF->insert(BBI, TrueBB);
     WorkList.push_back(CaseRec(TrueBB, C, CR.GE, LHSR));
+
+    // Put SV in a virtual register to make it available from the new blocks.
+    ExportFromCurrentBlock(SV);
   }
 
   // Similar to the optimization above, if the Value being switched on is
@@ -1888,6 +1892,9 @@ bool SelectionDAGLowering::handleBTSplitSwitchCase(CaseRec& CR,
     FalseBB = CurMF->CreateMachineBasicBlock(LLVMBB);
     CurMF->insert(BBI, FalseBB);
     WorkList.push_back(CaseRec(FalseBB,CR.LT,C,RHSR));
+
+    // Put SV in a virtual register to make it available from the new blocks.
+    ExportFromCurrentBlock(SV);
   }
 
   // Create a CaseBlock record representing a conditional branch to
@@ -2013,6 +2020,9 @@ bool SelectionDAGLowering::handleBitTestsSwitchCase(CaseRec& CR,
     BTC.push_back(BitTestCase(CasesBits[i].Mask,
                               CaseBB,
                               CasesBits[i].BB));
+
+    // Put SV in a virtual register to make it available from the new blocks.
+    ExportFromCurrentBlock(SV);
   }
 
   BitTestBlock BTB(lowBound, cmpRange, SV,