If a target zero or sign extends the result of its setcc, allow folding of

this into sign/zero extension instructions later.

On PPC, for example, this testcase:

%G = external global sbyte
implementation
void %test(int %X, int %Y) {
  %C = setlt int %X, %Y
  %D = cast bool %C to sbyte
  store sbyte %D, sbyte* %G
  ret void
}

Now codegens to:

        cmpw cr0, r3, r4
        li r3, 1
        li r4, 0
        blt .LBB_test_2 ;
.LBB_test_1:    ;
        or r3, r4, r4
.LBB_test_2:    ;
        addis r2, r2, ha16(L_G$non_lazy_ptr-"L00000$pb")
        lwz r2, lo16(L_G$non_lazy_ptr-"L00000$pb")(r2)
        stb r3, 0(r2)

instead of:

        cmpw cr0, r3, r4
        li r3, 1
        li r4, 0
        blt .LBB_test_2 ;
.LBB_test_1:    ;
        or r3, r4, r4
.LBB_test_2:    ;
***     rlwinm r3, r3, 0, 31, 31
        addis r2, r2, ha16(L_G$non_lazy_ptr-"L00000$pb")
        lwz r2, lo16(L_G$non_lazy_ptr-"L00000$pb")(r2)
        stb r3, 0(r2)

llvm-svn: 21148

1 files changed, 13 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 7faf19fd72f..04ccc77b6bb 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -585,7 +585,7 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
     break;
   case ISD::ZERO_EXTEND:
     if (Operand.getValueType() == VT) return Operand;   // noop extension
-    if (OpOpcode == ISD::ZERO_EXTEND)
+    if (OpOpcode == ISD::ZERO_EXTEND)   // (zext (zext x)) -> (zext x)
       return getNode(ISD::ZERO_EXTEND, VT, Operand.Val->getOperand(0));
     break;
   case ISD::TRUNCATE:
@@ -1025,6 +1025,18 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,SDOperand N1,
         return N1;
     }
 
+    // If we are extending the result of a setcc, and we already know the
+    // contents of the top bits, eliminate the extension.
+    if (N1.getOpcode() == ISD::SETCC)
+      switch (TLI.getSetCCResultContents()) {
+      case TargetLowering::UndefinedSetCCResult: break;
+      case TargetLowering::ZeroOrOneSetCCResult:
+        if (Opcode == ISD::ZERO_EXTEND_INREG) return N1;
+        break;
+      case TargetLowering::ZeroOrNegativeOneSetCCResult:
+        if (Opcode == ISD::SIGN_EXTEND_INREG) return N1;
+        break;
+      }
     break;
   }