From 8a7186dbc2df4879f511b2ae6f2bce25ad37d965 Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Thu, 6 Dec 2012 01:28:01 +0000
Subject: Let targets provide hooks that compute known zero and ones for
 any_extend and extload's. If they are implemented as zero-extend, or
 implicitly zero-extend, then this can enable more demanded bits
 optimizations. e.g.

define void @foo(i16* %ptr, i32 %a) nounwind {
entry:
  %tmp1 = icmp ult i32 %a, 100
  br i1 %tmp1, label %bb1, label %bb2
bb1:
  %tmp2 = load i16* %ptr, align 2
  br label %bb2
bb2:
  %tmp3 = phi i16 [ 0, %entry ], [ %tmp2, %bb1 ]
  %cmp = icmp ult i16 %tmp3, 24
  br i1 %cmp, label %bb3, label %exit
bb3:
  call void @bar() nounwind
  br label %exit
exit:
  ret void
}

This compiles to the followings before:
        push    {lr}
        mov     r2, #0
        cmp     r1, #99
        bhi     LBB0_2
@ BB#1:                                 @ %bb1
        ldrh    r2, [r0]
LBB0_2:                                 @ %bb2
        uxth    r0, r2
        cmp     r0, #23
        bhi     LBB0_4
@ BB#3:                                 @ %bb3
        bl      _bar
LBB0_4:                                 @ %exit
        pop     {lr}
        bx      lr

The uxth is not needed since ldrh implicitly zero-extend the high bits. With
this change it's eliminated.

rdar://12771555


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169459 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/SelectionDAG.cpp   | 10 +++-------
 lib/CodeGen/SelectionDAG/TargetLowering.cpp | 24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 7 deletions(-)

(limited to 'lib/CodeGen')

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 7dd57d5420..631449ca79 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1930,6 +1930,8 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, APInt &KnownZero,
       KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - MemBits);
     } else if (const MDNode *Ranges = LD->getRanges()) {
       computeMaskedBitsLoad(*Ranges, KnownZero);
+    } else if (ISD::isEXTLoad(Op.getNode())) {
+      TLI.computeMaskedBitsForAnyExtend(Op, KnownZero, KnownOne, *this, Depth);
     }
     return;
   }
@@ -1972,13 +1974,7 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, APInt &KnownZero,
     return;
   }
   case ISD::ANY_EXTEND: {
-    EVT InVT = Op.getOperand(0).getValueType();
-    unsigned InBits = InVT.getScalarType().getSizeInBits();
-    KnownZero = KnownZero.trunc(InBits);
-    KnownOne = KnownOne.trunc(InBits);
-    ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
-    KnownZero = KnownZero.zext(BitWidth);
-    KnownOne = KnownOne.zext(BitWidth);
+    TLI.computeMaskedBitsForAnyExtend(Op, KnownZero, KnownOne, *this, Depth);
     return;
   }
   case ISD::TRUNCATE: {
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 931c569d42..b410988dbd 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1856,6 +1856,30 @@ void TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
   KnownZero = KnownOne = APInt(KnownOne.getBitWidth(), 0);
 }
 
+void TargetLowering::computeMaskedBitsForAnyExtend(const SDValue Op,
+                                                   APInt &KnownZero,
+                                                   APInt &KnownOne,
+                                                   const SelectionDAG &DAG,
+                                                   unsigned Depth) const {
+  unsigned BitWidth = Op.getValueType().getScalarType().getSizeInBits();
+  if (Op.getOpcode() == ISD::ANY_EXTEND) {
+    EVT InVT = Op.getOperand(0).getValueType();
+    unsigned InBits = InVT.getScalarType().getSizeInBits();
+    KnownZero = KnownZero.trunc(InBits);
+    KnownOne = KnownOne.trunc(InBits);
+    DAG.ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
+    KnownZero = KnownZero.zext(BitWidth);
+    KnownOne = KnownOne.zext(BitWidth);
+    return;
+  } else if (ISD::isEXTLoad(Op.getNode())) {
+    KnownZero = KnownOne = APInt(BitWidth, 0);
+    return;
+  }
+  
+  assert(0 && "Expecting an ANY_EXTEND or extload!");
+}
+
+
 /// ComputeNumSignBitsForTargetNode - This method can be implemented by
 /// targets that want to expose additional information about sign bits to the
 /// DAG Combiner.
-- 
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