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Fold the PPCISD shifts when presented with 0 inputs. This occurs for code

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like:
long long test(long long X, int Y) {
  return 1ULL << Y;
}
long long test2(long long X, int Y) {
  return -1LL << Y;
}

which we used to compile to:

_test:
        li r2, 1
        subfic r3, r5, 32
        li r4, 0
        addi r6, r5, -32
        srw r3, r2, r3
        slw r4, r4, r5
        slw r6, r2, r6
        or r3, r4, r3
        slw r4, r2, r5
        or r3, r3, r6
        blr
_test2:
        li r2, -1
        subfic r3, r5, 32
        addi r6, r5, -32
        srw r3, r2, r3
        slw r4, r2, r5
        slw r2, r2, r6
        or r3, r4, r3
        or r3, r3, r2
        blr

Now we produce:

_test:
        li r2, 1
        addi r3, r5, -32
        subfic r4, r5, 32
        slw r3, r2, r3
        srw r4, r2, r4
        or r3, r4, r3
        slw r4, r2, r5
        blr
_test2:
        li r2, -1
        subfic r3, r5, 32
        addi r6, r5, -32
        srw r3, r2, r3
        slw r4, r2, r5
        slw r2, r2, r6
        or r3, r4, r3
        or r3, r3, r2
        blr


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30479 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2006-09-19 05:22:59 +00:00
parent 863ac769b8
commit cf9d0acfef
1 changed files with 20 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
lib/Target/PowerPC/PPCISelLowering.cpp
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@@ -2309,6 +2309,26 @@ SDOperand PPCTargetLowering::PerformDAGCombine(SDNode *N,
SelectionDAG &DAG = DCI.DAG;
switch (N->getOpcode()) {
default: break;
case PPCISD::SHL:
if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N->getOperand(0))) {
if (C->getValue() == 0) // 0 << V -> 0.
return N->getOperand(0);
}
break;
case PPCISD::SRL:
if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N->getOperand(0))) {
if (C->getValue() == 0) // 0 >>u V -> 0.
return N->getOperand(0);
}
break;
case PPCISD::SRA:
if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N->getOperand(0))) {
if (C->getValue() == 0 || // 0 >>s V -> 0.
C->isAllOnesValue()) // -1 >>s V -> -1.
return N->getOperand(0);
}
break;
case ISD::SINT_TO_FP:
if (TM.getSubtarget<PPCSubtarget>().has64BitSupport()) {
if (N->getOperand(0).getOpcode() == ISD::FP_TO_SINT) {