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Teach SCEVExpander to expand arithmetic involving pointers into GEP

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instructions. It attempts to create high-level multi-operand GEPs,
though in cases where this isn't possible it falls back to casting
the pointer to i8* and emitting a GEP with that. Using GEP instructions
instead of ptrtoint+arithmetic+inttoptr helps pointer analyses that
don't use ScalarEvolution, such as BasicAliasAnalysis.

Also, make the AddrModeMatcher more aggressive in handling GEPs.
Previously it assumed that operand 0 of a GEP would require a register
in almost all cases. It now does extra checking and can do more
matching if operand 0 of the GEP is foldable. This fixes a problem
that was exposed by SCEVExpander using GEPs.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72093 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2009-05-19 02:15:55 +00:00
parent fb57f1c8ec
commit 5be18e8476
9 changed files with 270 additions and 72 deletions
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61
lib/Transforms/Utils/AddrModeMatcher.cpp
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@ -255,43 +255,44 @@ bool AddressingModeMatcher::MatchOperationAddr(User *AddrInst, unsigned Opcode,
// Save the valid addressing mode in case we can't match.
ExtAddrMode BackupAddrMode = AddrMode;
// Check that this has no base reg yet. If so, we won't have a place to
// put the base of the GEP (assuming it is not a null ptr).
bool SetBaseReg = true;
if (isa<ConstantPointerNull>(AddrInst->getOperand(0)))
SetBaseReg = false; // null pointer base doesn't need representation.
else if (AddrMode.HasBaseReg)
return false; // Base register already specified, can't match GEP.
else {
// Otherwise, we'll use the GEP base as the BaseReg.
unsigned OldSize = AddrModeInsts.size();
// See if the scale and offset amount is valid for this target.
AddrMode.BaseOffs += ConstantOffset;
// Match the base operand of the GEP.
if (!MatchAddr(AddrInst->getOperand(0), Depth+1)) {
// If it couldn't be matched, just stuff the value in a register.
if (AddrMode.HasBaseReg) {
AddrMode = BackupAddrMode;
AddrModeInsts.resize(OldSize);
return false;
}
AddrMode.HasBaseReg = true;
AddrMode.BaseReg = AddrInst->getOperand(0);
}
// See if the scale and offset amount is valid for this target.
AddrMode.BaseOffs += ConstantOffset;
// Match the remaining variable portion of the GEP.
if (!MatchScaledValue(AddrInst->getOperand(VariableOperand), VariableScale,
Depth)) {
// If it couldn't be matched, try stuffing the base into a register
// instead of matching it, and retrying the match of the scale.
AddrMode = BackupAddrMode;
return false;
AddrModeInsts.resize(OldSize);
if (AddrMode.HasBaseReg)
return false;
AddrMode.HasBaseReg = true;
AddrMode.BaseReg = AddrInst->getOperand(0);
AddrMode.BaseOffs += ConstantOffset;
if (!MatchScaledValue(AddrInst->getOperand(VariableOperand),
VariableScale, Depth)) {
// If even that didn't work, bail.
AddrMode = BackupAddrMode;
AddrModeInsts.resize(OldSize);
return false;
}
}
// If we have a null as the base of the GEP, folding in the constant offset
// plus variable scale is all we can do.
if (!SetBaseReg) return true;
// If this match succeeded, we know that we can form an address with the
// GepBase as the basereg. Match the base pointer of the GEP more
// aggressively by zeroing out BaseReg and rematching. If the base is
// (for example) another GEP, this allows merging in that other GEP into
// the addressing mode we're forming.
AddrMode.HasBaseReg = false;
AddrMode.BaseReg = 0;
bool Success = MatchAddr(AddrInst->getOperand(0), Depth+1);
assert(Success && "MatchAddr should be able to fill in BaseReg!");
Success=Success;
return true;
}
}