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Check for non-static allocas #774

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Merged
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Feb 24, 2020
Merged

Check for non-static allocas #774

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18 changes: 18 additions & 0 deletions compiler/check.go
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,24 @@ func (c *Compiler) checkInstruction(inst llvm.Value, types map[llvm.Type]struct{
return errorAt(inst, err.Error())
}

// The alloca instruction can be present in every basic block. However,
// allocas in basic blocks other than the entry basic block have a number of
// problems:
// * They are hard to optimize, leading to potential missed optimizations.
// * They may cause stack overflows in loops that would otherwise be
// innocent.
// * They cause extra code to be generated, because it requires the use of
// a frame pointer.
// * Perhaps most importantly, the coroutine lowering pass of LLVM (as of
// LLVM 9) cannot deal with these allocas:
// https://llvm.org/docs/Coroutines.html
// Therefore, alloca instructions should be limited to the entry block.
if !inst.IsAAllocaInst().IsNil() {
if inst.InstructionParent() != inst.InstructionParent().Parent().EntryBasicBlock() {
return errorAt(inst, "internal error: non-static alloca")
}
}

// check operands
for i := 0; i < inst.OperandsCount(); i++ {
if err := c.checkValue(inst.Operand(i), types, specials); err != nil {
Expand Down