Avoid non-static allocas in WebAssembly

[aykevl]

This PR comes in two parts:

1. A refactor that makes the wasm ABI testable.
2. A small commit that moves temporary allocas to the entry block, which should fix some cases of LLVM ERROR: Coroutines cannot handle non static allocas yet #234 and Possibly spurious error: LLVM ERROR: Coroutines cannot handle non static allocas yet #421.

There are possible future improvements (such as the readonly attribute) but I left them alone for now as that's not needed to fix these bugs.

[aykevl]

I modified the first commit a bit (https://github.com/tinygo-org/tinygo/compare/aa05d54db780c99ae34f0bd6a5f01a788345b79b..1f2982b22f3fd6d004668504c360cef2ad23f258) because there was a bug in the transform (surfacing only with the added tests) that caused CI to fail.

[aykevl]

I saw some more non static allocas. I think they are created by the coroutine lowering pass (@jaddr2line).

This is the IR I found:

define internal fastcc { %"github.com/aykevl/go-smartwatch.Watch"*, %runtime._interface } @"github.com/aykevl/go-smartwatch.Open"(i8* nocapture readnone %context, i8* %parentHandle) unnamed_addr #0 section ".text.github.com/aykevl/go-smartwatch.Open" !dbg !2376 {
entry:
  %complit17.i = alloca %"tinygo.org/x/drivers/st7789.Device", align 8, !dbg !2378
  %complit10.i = alloca %machine.PinConfig, align 8, !dbg !2378
  %complit3.i = alloca %machine.PinConfig, align 8, !dbg !2378
  %complit.i = alloca %machine.PinConfig, align 8, !dbg !2378
  %bus.i = alloca %machine.SPI, align 8, !dbg !2378
  %config.i = alloca i64, align 8, !dbg !2392
  %spi.i = alloca %machine.SPI, align 8, !dbg !2392
  %task.state = alloca %runtime.taskState, align 8, !dbg !2408
  %task.token = call token @llvm.coro.id(i32 0, i8* nonnull null, i8* bitcast ({ %"github.com/aykevl/go-smartwatch.Watch"*, %runtime._interface } (i8*, i8*)* @"github.com/aykevl/go-smartwatch.Open" to i8*), i8* null), !dbg !2408
  %task.size = tail call i32 @llvm.coro.size.i32(), !dbg !2408
  %task.data = tail call fastcc i8* @runtime.alloc(i32 %task.size), !dbg !2408
  %task.handle = call noalias nonnull i8* @llvm.coro.begin(token %task.token, i8* nonnull %task.data), !dbg !2408
  %FramePtr = bitcast i8* %task.handle to %"github.com/aykevl/go-smartwatch.Open.Frame"*, !dbg !2408
  %parentHandle.spill.addr = getelementptr inbounds %"github.com/aykevl/go-smartwatch.Open.Frame", %"github.com/aykevl/go-smartwatch.Open.Frame"* %FramePtr, i32 0, i32 4, !dbg !2408
  store i8* %parentHandle, i8** %parentHandle.spill.addr, !dbg !2408
  tail call void @runtime.trackPointer(i8* nonnull %task.data, i8* undef, i8* null), !dbg !2408
  call void @llvm.dbg.value(metadata i8* %parentHandle, metadata !2409, metadata !DIExpression()), !dbg !2412
  %0 = icmp eq i8* %parentHandle, null, !dbg !2414
  br i1 %0, label %if.then.i, label %runtime.getTaskStatePtr.exit, !dbg !2415

if.then.i:                                        ; preds = %entry
  call fastcc void @runtime.blockingPanic(), !dbg !2416
  unreachable

runtime.getTaskStatePtr.exit:                     ; preds = %entry
  %1 = call fastcc %runtime.taskState* @"(*runtime.task).state"(i8* nonnull %parentHandle), !dbg !2417
  %2 = bitcast %runtime.taskState* %1 to i8*, !dbg !2417
  call void @runtime.trackPointer(i8* nonnull %2, i8* undef, i8* null), !dbg !2417
  %3 = getelementptr inbounds %runtime.taskState, %runtime.taskState* %1, i32 0, i32 1, !dbg !2418
  %4 = load i8*, i8** %3, align 4, !dbg !2418
  %.spill.addr = getelementptr inbounds %"github.com/aykevl/go-smartwatch.Open.Frame", %"github.com/aykevl/go-smartwatch.Open.Frame"* %FramePtr, i32 0, i32 5, !dbg !2418
  store i8* %4, i8** %.spill.addr, !dbg !2418
  call void @runtime.trackPointer(i8* %4, i8* undef, i8* null), !dbg !2418
  %complit55 = alloca %machine.PinConfig, align 8, !dbg !2408
  %complit48 = alloca %machine.PinConfig, align 8, !dbg !2408
  %complit37 = alloca %"tinygo.org/x/drivers/st7789.Config", align 8, !dbg !2408
  %complit30 = alloca %machine.PinConfig, align 8, !dbg !2408
  %complit = alloca i64, align 8, !dbg !2408
  %tmpcast = bitcast i64* %complit to %machine.SPIConfig*, !dbg !2408
  %spi = alloca %machine.SPI, align 8, !dbg !2408
  %5 = load %"github.com/aykevl/go-smartwatch.Watch"*, %"github.com/aykevl/go-smartwatch.Watch"** @"github.com/aykevl/go-smartwatch.watch", align 4, !dbg !2408
  %6 = bitcast %"github.com/aykevl/go-smartwatch.Watch"* %5 to i8*, !dbg !2408
  call void @runtime.trackPointer(i8* %6, i8* undef, i8* null), !dbg !2408
  %7 = icmp eq %"github.com/aykevl/go-smartwatch.Watch"* %5, null, !dbg !2419
  br i1 %7, label %if.done, label %if.then, !dbg !2420

Before, it was this IR:

define internal fastcc { %"github.com/aykevl/go-smartwatch.Watch"*, %runtime._interface } @"github.com/aykevl/go-smartwatch.Open"(i8* %context, i8* %parentHandle) unnamed_addr #6 section ".text.github.com/aykevl/go-smartwatch.Open" !dbg !2779 {
entry:
  %task.state = alloca %runtime.taskState, !dbg !2781
  %task.state.i8 = bitcast %runtime.taskState* %task.state to i8*, !dbg !2781
  %task.token = call token @llvm.coro.id(i32 0, i8* %task.state.i8, i8* bitcast ({ %"github.com/aykevl/go-smartwatch.Watch"*, %runtime._interface } (i8*, i8*)* @"github.com/aykevl/go-smartwatch.Open" to i8*), i8* null), !dbg !2781
  %task.size = call i32 @llvm.coro.size.i32(), !dbg !2781
  %task.data = call i8* @runtime.alloc(i32 %task.size, i8* undef, i8* null), !dbg !2781
  call void @runtime.trackPointer(i8* %task.data, i8* undef, i8* null), !dbg !2781
  %task.handle = call i8* @llvm.coro.begin(token %task.token, i8* %task.data) #13, !dbg !2781
  %0 = call i8* @runtime.getTaskStatePtr(i8* %parentHandle, i8* undef, i8* null), !dbg !2781
  %retPtr = bitcast i8* %0 to { %"github.com/aykevl/go-smartwatch.Watch"*, %runtime._interface }*, !dbg !2781
  %complit55 = alloca %machine.PinConfig, !dbg !2781
  %complit48 = alloca %machine.PinConfig, !dbg !2781
  %complit37 = alloca %"tinygo.org/x/drivers/st7789.Config", !dbg !2781
  %complit30 = alloca %machine.PinConfig, !dbg !2781
  %complit = alloca %machine.SPIConfig, !dbg !2781
  %spi = alloca %machine.SPI, !dbg !2781
  %1 = load %"github.com/aykevl/go-smartwatch.Watch"*, %"github.com/aykevl/go-smartwatch.Watch"** @"github.com/aykevl/go-smartwatch.watch", !dbg !2781
  %2 = bitcast %"github.com/aykevl/go-smartwatch.Watch"* %1 to i8*, !dbg !2781
  call void @runtime.trackPointer(i8* %2, i8* undef, i8* null), !dbg !2781
  %3 = icmp ne %"github.com/aykevl/go-smartwatch.Watch"* %1, null, !dbg !2782
  br i1 %3, label %if.then, label %if.done, !dbg !2783

But that (unrelated?) issue shouldn't hold back this PR.

[deadprogram]

@justinclift if you have time to try this out... :)

[justinclift]

Maybe next week, definitely not this week though. 😉

[niaow]

This looks ok. Can merge after tested by someone who uses wasm more.

[deadprogram]

Anything stopping this PR from bring merged now?

[aykevl]

Yes, this should be mergeable. The first is a refactor (plus small bugfix as indicated above) and the second is a fix for a bug that has been a problem for WebAssembly for some time.

[deadprogram]

OK, merging then. Thanks!