This is another case where instcombine demanded bits optimization created

large immediates. Add dag combine logic to recover in case the large
immediates doesn't fit in cmp immediate operand field.

int foo(unsigned long l) {
  return (l>> 47) == 1;
}

we produce

  %shr.mask = and i64 %l, -140737488355328
  %cmp = icmp eq i64 %shr.mask, 140737488355328
  %conv = zext i1 %cmp to i32
  ret i32 %conv

which codegens to

movq    $0xffff800000000000,%rax
andq    %rdi,%rax
movq    $0x0000800000000000,%rcx
cmpq    %rcx,%rax
sete    %al
movzbl    %al,%eax
ret

TargetLowering::SimplifySetCC would transform
(X & -256) == 256 -> (X >> 8) == 1
if the immediate fails the isLegalICmpImmediate() test. For x86,
that's immediates which are not a signed 32-bit immediate.

Based on a patch by Eli Friedman.

PR10328
rdar://9758774

llvm-svn: 160346

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 891d401201f..9902ed76fa7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -2322,6 +2322,27 @@ TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
           }
         }
       }
+
+    if (!isLegalICmpImmediate(C1.getSExtValue())) {
+      // (X & -256) == 256 -> (X >> 8) == 1
+      if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
+          N0.getOpcode() == ISD::AND && N0.hasOneUse()) {
+        if (ConstantSDNode *AndRHS =
+            dyn_cast<ConstantSDNode>(N0.getOperand(1))) {
+          const APInt &AndRHSC = AndRHS->getAPIntValue();
+          if ((-AndRHSC).isPowerOf2() && (AndRHSC & C1) == C1) {
+            unsigned ShiftBits = AndRHSC.countTrailingZeros();
+            EVT ShiftTy = DCI.isBeforeLegalize() ?
+              getPointerTy() : getShiftAmountTy(N0.getValueType());
+            EVT CmpTy = N0.getValueType();
+            SDValue Shift = DAG.getNode(ISD::SRL, dl, CmpTy, N0.getOperand(0),
+                                        DAG.getConstant(ShiftBits, ShiftTy));
+            SDValue CmpRHS = DAG.getConstant(C1.lshr(ShiftBits), CmpTy);
+            return DAG.getSetCC(dl, VT, Shift, CmpRHS, Cond);
+          }
+        }
+      }
+    }
   }
 
   if (isa<ConstantFPSDNode>(N0.getNode())) {