From 70e10d3fe4c5df189348f64fce56254a5a32b51c Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Tue, 17 Jul 2012 06:53:39 +0000
Subject: 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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160346 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/TargetLowering.cpp | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

(limited to 'lib/CodeGen/SelectionDAG/TargetLowering.cpp')

diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 891d401201..9902ed76fa 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/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())) {
-- 
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