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3 changes, 2 of which are cleanup one of which changes codegen: 

1. Rearrange code a bit so that the special case doesn't require indenting lots
   of code.
2. Add comments describing PPC calling convention.
3. Only round up to 56-bytes of stack space for an outgoing call if the callee
   is varargs.  This saves a bit of stack space.

llvm-svn: 28342
This commit is contained in:
Chris Lattner 2006-05-17 00:15:40 +00:00
parent f058f5aef1
commit b7552a88d6
1 changed files with 111 additions and 105 deletions
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24
llvm/lib/Target/PowerPC/PPCISelLowering.cpp
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@ -889,19 +889,26 @@ static SDOperand LowerCALL(SDOperand Op, SelectionDAG &DAG) {
std::vector<SDOperand> args_to_use;
// Count how many bytes are to be pushed on the stack, including the linkage
// area, and parameter passing area.
// area, and parameter passing area. We start with 24 bytes, which is
// prereserved space for [SP][CR][LR][3 x unused].
unsigned NumBytes = 24;
if (Op.getNumOperands() == 5) {
Chain = DAG.getCALLSEQ_START(Chain, DAG.getConstant(NumBytes, MVT::i32));
} else {
// Add up all the space actually used.
for (unsigned i = 5, e = Op.getNumOperands(); i != e; ++i)
NumBytes += MVT::getSizeInBits(Op.getOperand(i).getValueType())/8;
// Just to be safe, we'll always reserve the full 24 bytes of linkage area
// plus 32 bytes of argument space in case any called code gets funky on us.
// (Required by ABI to support var arg)
if (NumBytes < 56) NumBytes = 56;
// If we are calling what looks like a varargs function on the caller side,
// there are two cases:
// 1) The callee uses va_start.
// 2) The callee doesn't use va_start.
//
// In the case of #1, the prolog code will store up to 8 GPR argument
// registers to the stack, allowing va_start to index over them in memory.
// Because we cannot tell the difference (on the caller side) between #1/#2,
// we have to conservatively assume we have #1. As such, make sure we have
// at least enough stack space for the caller to store the 8 GPRs.
if (isVarArg && Op.getNumOperands() > 5 && NumBytes < 56)
NumBytes = 56;
// Adjust the stack pointer for the new arguments...
// These operations are automatically eliminated by the prolog/epilog pass
@ -1002,7 +1009,6 @@ static SDOperand LowerCALL(SDOperand Op, SelectionDAG &DAG) {
}
if (!MemOps.empty())
Chain = DAG.getNode(ISD::TokenFactor, MVT::Other, MemOps);
}
std::vector<MVT::ValueType> RetVals(Op.Val->value_begin(),
Op.Val->value_end());