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Teach the optimizer to delete zero sized alloca's (but not mallocs!)

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12507 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-03-19 06:08:10 +00:00
parent f3fbddd333
commit 7c881dffc9
1 changed files with 12 additions and 4 deletions
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16
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -2367,11 +2367,13 @@ Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
// Create and insert the replacement instruction...
if (isa<MallocInst>(AI))
New = new MallocInst(NewTy, 0, AI.getName(), &AI);
New = new MallocInst(NewTy, 0, AI.getName());
else {
assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
New = new AllocaInst(NewTy, 0, AI.getName(), &AI);
New = new AllocaInst(NewTy, 0, AI.getName());
}
InsertNewInstBefore(New, AI);
// Scan to the end of the allocation instructions, to skip over a block of
// allocas if possible...
@ -2387,9 +2389,15 @@ Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
// Now make everything use the getelementptr instead of the original
// allocation.
ReplaceInstUsesWith(AI, V);
return &AI;
return ReplaceInstUsesWith(AI, V);
}
// If alloca'ing a zero byte object, replace the alloca with a null pointer.
// Note that we only do this for alloca's, because malloc should allocate and
// return a unique pointer, even for a zero byte allocation.
if (isa<AllocaInst>(AI) && TD->getTypeSize(AI.getAllocatedType()) == 0)
return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
return 0;
}