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
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 931c569..b410988 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1856,6 +1856,30 @@
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.