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compiler: fix escapes due to nil checks

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Some tests get bigger, most get smaller. However, all tested driver
examples get smaller in size showing that this is a good change in the
real world.
This commit is contained in:
Ayke van Laethem
2019-03-30 13:14:04 +01:00
committed by Ron Evans
parent cd8471acae
commit d653088cbe
4 changed files with 46 additions and 2 deletions
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compiler/asserts.go
+17 -2
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@@ -115,8 +115,23 @@ func (c *Compiler) emitNilCheck(frame *Frame, ptr llvm.Value, blockPrefix string
frame.blockExits[frame.currentBlock] = nextBlock // adjust outgoing block for phi nodes
// Compare against nil.
nilptr := llvm.ConstPointerNull(ptr.Type())
isnil := c.builder.CreateICmp(llvm.IntEQ, ptr, nilptr, "")
var isnil llvm.Value
if ptr.Type().PointerAddressSpace() == 0 {
// Do the nil check using the isnil builtin, which marks the parameter
// as nocapture.
// The reason it has to go through a builtin, is that a regular icmp
// instruction may capture the pointer in LLVM semantics, see
// https://reviews.llvm.org/D60047 for details. Pointer capturing
// unfortunately breaks escape analysis, so we use this trick to let the
// functionattr pass know that this pointer doesn't really escape.
ptr = c.builder.CreateBitCast(ptr, c.i8ptrType, "")
isnil = c.createRuntimeCall("isnil", []llvm.Value{ptr}, "")
} else {
// Do the nil check using a regular icmp. This can happen with function
// pointers on AVR, which don't benefit from escape analysis anyway.
nilptr := llvm.ConstPointerNull(ptr.Type())
isnil = c.builder.CreateICmp(llvm.IntEQ, ptr, nilptr, "")
}
c.builder.CreateCondBr(isnil, faultBlock, nextBlock)
// Fail: this is a nil pointer, exit with a panic.