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Teach the optimizer to delete zero sized alloca's (but not mallocs!)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12507 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -2367,11 +2367,13 @@ Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
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// Create and insert the replacement instruction...
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if (isa<MallocInst>(AI))
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New = new MallocInst(NewTy, 0, AI.getName(), &AI);
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New = new MallocInst(NewTy, 0, AI.getName());
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else {
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assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
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New = new AllocaInst(NewTy, 0, AI.getName(), &AI);
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New = new AllocaInst(NewTy, 0, AI.getName());
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}
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InsertNewInstBefore(New, AI);
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// Scan to the end of the allocation instructions, to skip over a block of
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// allocas if possible...
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@ -2387,9 +2389,15 @@ Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
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// Now make everything use the getelementptr instead of the original
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// allocation.
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ReplaceInstUsesWith(AI, V);
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return &AI;
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return ReplaceInstUsesWith(AI, V);
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}
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// If alloca'ing a zero byte object, replace the alloca with a null pointer.
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// Note that we only do this for alloca's, because malloc should allocate and
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// return a unique pointer, even for a zero byte allocation.
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if (isa<AllocaInst>(AI) && TD->getTypeSize(AI.getAllocatedType()) == 0)
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return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
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return 0;
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}
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