compiler: add support for new unsafe slice/string functions

This adds support for unsafe.SliceData, unsafe.String, and
unsafe.SringData that were introduced in Go 1.20.

compiler/testdata/go1.20.go

@@ -0,0 +1,15 @@
+package main
+
+import "unsafe"
+
+func unsafeSliceData(s []int) *int {
+	return unsafe.SliceData(s)
+}
+
+func unsafeString(ptr *byte, len int16) string {
+	return unsafe.String(ptr, len)
+}
+
+func unsafeStringData(s string) *byte {
+	return unsafe.StringData(s)
+}

compiler/testdata/go1.20.ll

@@ -0,0 +1,58 @@
+; ModuleID = 'go1.20.go'
+source_filename = "go1.20.go"
+target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128-ni:1:10:20"
+target triple = "wasm32-unknown-wasi"
+
+%runtime._string = type { ptr, i32 }
+
+declare noalias nonnull ptr @runtime.alloc(i32, ptr, ptr) #0
+
+declare void @runtime.trackPointer(ptr nocapture readonly, ptr) #0
+
+; Function Attrs: nounwind
+define hidden void @main.init(ptr %context) unnamed_addr #1 {
+entry:
+  ret void
+}
+
+; Function Attrs: nounwind
+define hidden ptr @main.unsafeSliceData(ptr %s.data, i32 %s.len, i32 %s.cap, ptr %context) unnamed_addr #1 {
+entry:
+  call void @runtime.trackPointer(ptr %s.data, ptr undef) #2
+  ret ptr %s.data
+}
+
+; Function Attrs: nounwind
+define hidden %runtime._string @main.unsafeString(ptr dereferenceable_or_null(1) %ptr, i16 %len, ptr %context) unnamed_addr #1 {
+entry:
+  %0 = icmp slt i16 %len, 0
+  %1 = icmp eq ptr %ptr, null
+  %2 = icmp ne i16 %len, 0
+  %3 = and i1 %1, %2
+  %4 = or i1 %3, %0
+  br i1 %4, label %unsafe.String.throw, label %unsafe.String.next
+
+unsafe.String.next:                               ; preds = %entry
+  %5 = zext i16 %len to i32
+  %6 = insertvalue %runtime._string undef, ptr %ptr, 0
+  %7 = insertvalue %runtime._string %6, i32 %5, 1
+  call void @runtime.trackPointer(ptr %ptr, ptr undef) #2
+  ret %runtime._string %7
+
+unsafe.String.throw:                              ; preds = %entry
+  call void @runtime.unsafeSlicePanic(ptr undef) #2
+  unreachable
+}
+
+declare void @runtime.unsafeSlicePanic(ptr) #0
+
+; Function Attrs: nounwind
+define hidden ptr @main.unsafeStringData(ptr %s.data, i32 %s.len, ptr %context) unnamed_addr #1 {
+entry:
+  call void @runtime.trackPointer(ptr %s.data, ptr undef) #2
+  ret ptr %s.data
+}
+
+attributes #0 = { "target-features"="+bulk-memory,+nontrapping-fptoint,+sign-ext" }
+attributes #1 = { nounwind "target-features"="+bulk-memory,+nontrapping-fptoint,+sign-ext" }
+attributes #2 = { nounwind }