[PATCH] D139645: [WebAssembly] Fold adds with global addresses into load offset

[Luke Lau via Phabricator via llvm-commits]

luke added inline comments.


================
Comment at: llvm/test/CodeGen/WebAssembly/userstack.ll:336
+; global address, so we should fold the global address into the offset, but not
+; the frame offset.
 ; CHECK-LABEL: frame_offset_with_global_address
----------------
dschuff wrote:
> so the result of this is that the frame offset will end up in a const or add expression (consumed by the i32.load8_u), and the global address will be folded?
> Is this better than what we did before (i.e. the address in a const and the frame offset folded)?
In this case the frame offset wasn't being folded, although I'm not sure if that is intentional or not. This is the codegen before the patch:

```
frame_offset_with_global_address:
	.functype	frame_offset_with_global_address () -> (i32)
	i32.const	$push0=, str
	global.get	$push5=, __stack_pointer
	i32.const	$push6=, 16
	i32.sub 	$push9=, $pop5, $pop6
	i32.const	$push7=, 12
	i32.add 	$push8=, $pop9, $pop7
	i32.add 	$push1=, $pop0, $pop8
	i32.load8_u	$push2=, 0($pop1)
	i32.const	$push3=, 67
	i32.and 	$push4=, $pop2, $pop3
	return	$pop4
```

With the patch the global address gets folded in which saves a `const` and an `add` instruction:

```
frame_offset_with_global_address:
	.functype	frame_offset_with_global_address () -> (i32)
	global.get	$push3=, __stack_pointer
	i32.const	$push4=, 16
	i32.sub 	$push7=, $pop3, $pop4
	i32.const	$push5=, 12
	i32.add 	$push6=, $pop7, $pop5
	i32.load8_u	$push1=, str($pop6)
	i32.const	$push0=, 67
	i32.and 	$push2=, $pop1, $pop0
	return	$pop2
```




Repository:
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  https://reviews.llvm.org/D139645/new/

https://reviews.llvm.org/D139645