Changes in directory llvm/lib/CodeGen/SelectionDAG:
DAGCombiner.cpp updated: 1.57 -> 1.58
---
Log message:
Codegen mul by negative power of two with a shift and negate.
This implements test/Regression/CodeGen/PowerPC/mul-neg-power-2.ll,
producing:
_foo:
slwi r2, r3, 1
subfic r3, r2, 63
blr
instead of:
_foo:
mulli r2, r3, -2
addi r3, r2, 63
blr
---
Diffs of the changes: (+13 -3)
DAGCombiner.cpp | 16 +++++++++++++---
1 files changed, 13 insertions(+), 3 deletions(-)
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.57
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.58
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.57 Thu Oct 27 02:10:34 2005
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Sun Oct 30 01:41:49 2005
@@ -735,8 +735,7 @@
// fold (mul c1, c2) -> c1*c2
if (N0C && N1C)
- return DAG.getConstant(N0C->getValue() * N1C->getValue(),
- N->getValueType(0));
+ return DAG.getConstant(N0C->getValue() * N1C->getValue(), VT);
// canonicalize constant to RHS
if (N0C && !N1C)
return DAG.getNode(ISD::MUL, VT, N1, N0);
@@ -748,9 +747,20 @@
return DAG.getNode(ISD::SUB, VT, DAG.getConstant(0, VT), N0);
// fold (mul x, (1 << c)) -> x << c
if (N1C && isPowerOf2_64(N1C->getValue()))
- return DAG.getNode(ISD::SHL, N->getValueType(0), N0,
+ return DAG.getNode(ISD::SHL, VT, N0,
DAG.getConstant(Log2_64(N1C->getValue()),
TLI.getShiftAmountTy()));
+ // fold (mul x, -(1 << c)) -> -(x << c) or (-x) << c
+ if (N1C && isPowerOf2_64(-N1C->getSignExtended())) {
+ // FIXME: If the input is something that is easily negated (e.g. a
+ // single-use add), we should put the negate there.
+ return DAG.getNode(ISD::SUB, VT, DAG.getConstant(0, VT),
+ DAG.getNode(ISD::SHL, VT, N0,
+ DAG.getConstant(Log2_64(-N1C->getSignExtended()),
+ TLI.getShiftAmountTy())));
+ }
+
+
// fold (mul (mul x, c1), c2) -> (mul x, c1*c2)
if (N1C && N0.getOpcode() == ISD::MUL) {
ConstantSDNode *N00C = dyn_cast<ConstantSDNode>(N0.getOperand(0));
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