[llvm-commits] CVS: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

[Chris Lattner]

Changes in directory llvm/lib/CodeGen/SelectionDAG:

SelectionDAG.cpp updated: 1.62 -> 1.63
---
Log message:

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)



---
Diffs of the changes:  (+13 -1)

 SelectionDAG.cpp |   14 +++++++++++++-
 1 files changed, 13 insertions(+), 1 deletion(-)


Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1.62 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1.63
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1.62	Thu Apr  7 13:58:54 2005
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp	Thu Apr  7 14:43:53 2005
@@ -585,7 +585,7 @@
     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 @@
         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;
   }