Changes in directory llvm/lib/CodeGen/SelectionDAG:
DAGCombiner.cpp updated: 1.138 -> 1.139
---
Log message:
Add a little dag combine to compile this:
int %AreSecondAndThirdElementsBothNegative(<4 x float>* %in) {
entry:
%tmp1 = load <4 x float>* %in ; <<4 x float>> [#uses=1]
%tmp = tail call int %llvm.ppc.altivec.vcmpgefp.p( int 1, <4 x float> <
float 0x7FF8000000000000, float 0.000000e+00, float 0.000000e+00, float
0x7FF8000000000000 >, <4 x float> %tmp1 ) ; <int> [#uses=1]
%tmp = seteq int %tmp, 0 ; <bool> [#uses=1]
%tmp3 = cast bool %tmp to int ; <int> [#uses=1]
ret int %tmp3
}
into this:
_AreSecondAndThirdElementsBothNegative:
mfspr r2, 256
oris r4, r2, 49152
mtspr 256: http://llvm.cs.uiuc.edu/PR256 , r4
li r4, lo16(LCPI1_0)
lis r5, ha16(LCPI1_0)
lvx v0, 0, r3
lvx v1, r5, r4
vcmpgefp. v0, v1, v0
mfcr r3, 2
rlwinm r3, r3, 27, 31, 31
mtspr 256: http://llvm.cs.uiuc.edu/PR256 , r2
blr
instead of this:
_AreSecondAndThirdElementsBothNegative:
mfspr r2, 256
oris r4, r2, 49152
mtspr 256: http://llvm.cs.uiuc.edu/PR256 , r4
li r4, lo16(LCPI1_0)
lis r5, ha16(LCPI1_0)
lvx v0, 0, r3
lvx v1, r5, r4
vcmpgefp. v0, v1, v0
mfcr r3, 2
rlwinm r3, r3, 27, 31, 31
xori r3, r3, 1
cntlzw r3, r3
srwi r3, r3, 5
mtspr 256: http://llvm.cs.uiuc.edu/PR256 , r2
blr
---
Diffs of the changes: (+33 -0)
DAGCombiner.cpp | 33 +++++++++++++++++++++++++++++++++
1 files changed, 33 insertions(+)
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.138
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.139
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.138 Sat Apr 1 21:25:57 2006
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Sun Apr 2 00:11:11 2006
@@ -1601,6 +1601,39 @@
return DAG.getNode(ISD::SRL, VT, N0.getOperand(0),
DAG.getConstant(c1 + c2, N1.getValueType()));
}
+
+ // fold (srl (ctlz x), "5") -> x iff x has one bit set (the low bit).
+ if (N1C && N0.getOpcode() == ISD::CTLZ &&
+ N1C->getValue() == Log2_32(MVT::getSizeInBits(VT))) {
+ uint64_t KnownZero, KnownOne, Mask = MVT::getIntVTBitMask(VT);
+ TLI.ComputeMaskedBits(N0.getOperand(0), Mask, KnownZero, KnownOne);
+
+ // If any of the input bits are KnownOne, then the input couldn't be all
+ // zeros, thus the result of the srl will always be zero.
+ if (KnownOne) return DAG.getConstant(0, VT);
+
+ // If all of the bits input the to ctlz node are known to be zero, then
+ // the result of the ctlz is "32" and the result of the shift is one.
+ uint64_t UnknownBits = ~KnownZero & Mask;
+ if (UnknownBits == 0) return DAG.getConstant(1, VT);
+
+ // Otherwise, check to see if there is exactly one bit input to the ctlz.
+ if ((UnknownBits & (UnknownBits-1)) == 0) {
+ // Okay, we know that only that the single bit specified by UnknownBits
+ // could be set on input to the CTLZ node. If this bit is set, the SRL
+ // will return 0, if it is clear, it returns 1. Change the CTLZ/SRL pair
+ // to an SRL,XOR pair, which is likely to simplify more.
+ unsigned ShAmt = CountTrailingZeros_64(UnknownBits);
+ SDOperand Op = N0.getOperand(0);
+ if (ShAmt) {
+ Op = DAG.getNode(ISD::SRL, VT, Op,
+ DAG.getConstant(ShAmt, TLI.getShiftAmountTy()));
+ AddToWorkList(Op.Val);
+ }
+ return DAG.getNode(ISD::XOR, VT, Op, DAG.getConstant(1, VT));
+ }
+ }
+
return SDOperand();
}
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