From e345d6fc4e3223e2d2655114c8829538276a0bb9 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Mon, 25 Oct 2021 16:58:15 -0700
Subject: decl: Allow alignment > 16 of locals

This is not yet supported by QBE, so for now we allocate a bit extra
and choose the address in the allocated region with an aligned
address.
---
 decl.c                    |  4 +---
 qbe.c                     | 12 ++++++++++--
 test/alignas-local-32.c   |  4 ++++
 test/alignas-local-32.qbe | 11 +++++++++++
 4 files changed, 26 insertions(+), 5 deletions(-)
 create mode 100644 test/alignas-local-32.c
 create mode 100644 test/alignas-local-32.qbe

diff --git a/decl.c b/decl.c
index 50fe1c6..268ee01 100644
--- a/decl.c
+++ b/decl.c
@@ -960,10 +960,8 @@ decl(struct scope *s, struct func *f)
 			if (init || d->linkage == LINKNONE) {
 				if (d->linkage != LINKNONE || sc & SCSTATIC)
 					emitdata(d, init);
-				else if (d->align <= 16)
-					funcinit(f, d, init);
 				else
-					error(&tok.loc, "unsupported alignment %d for object with automatic storage duration", d->align);
+					funcinit(f, d, init);
 				d->defined = true;
 				if (d->tentative.next)
 					listremove(&d->tentative);
diff --git a/qbe.c b/qbe.c
index 88cd97b..264bdac 100644
--- a/qbe.c
+++ b/qbe.c
@@ -259,6 +259,7 @@ funcalloc(struct func *f, struct decl *d)
 {
 	enum instkind op;
 	struct inst *inst;
+	unsigned long long size;
 
 	assert(!d->type->incomplete);
 	assert(d->type->size > 0);
@@ -266,17 +267,24 @@ funcalloc(struct func *f, struct decl *d)
 		d->align = d->type->align;
 	else if (d->align < d->type->align)
 		error(&tok.loc, "object requires alignment %d, which is stricter than %d", d->type->align, d->align);
+	size = d->type->size;
 	switch (d->align) {
 	case 1:
 	case 2:
 	case 4:  op = IALLOC4; break;
 	case 8:  op = IALLOC8; break;
+	default: size += d->align - 16; /* fallthrough */
 	case 16: op = IALLOC16; break;
-	default:
-		fatal("internal error: invalid alignment: %d\n", d->align);
 	}
 	inst = mkinst(f, op, ptrclass, mkintconst(size), NULL);
 	arrayaddptr(&f->start->insts, inst);
+	if (d->align > 16) {
+		/* TODO: implement alloc32 in QBE and use that instead */
+		inst = mkinst(f, IADD, ptrclass, &inst->res, mkintconst(d->align - 16));
+		arrayaddptr(&f->start->insts, inst);
+		inst = mkinst(f, IAND, ptrclass, &inst->res, mkintconst(-d->align));
+		arrayaddptr(&f->start->insts, inst);
+	}
 	d->value = &inst->res;
 }
 
diff --git a/test/alignas-local-32.c b/test/alignas-local-32.c
new file mode 100644
index 0000000..e69a105
--- /dev/null
+++ b/test/alignas-local-32.c
@@ -0,0 +1,4 @@
+int main(void) {
+	_Alignas(32) char x;
+	return (unsigned long)&x % 32;
+}
diff --git a/test/alignas-local-32.qbe b/test/alignas-local-32.qbe
new file mode 100644
index 0000000..53bfab3
--- /dev/null
+++ b/test/alignas-local-32.qbe
@@ -0,0 +1,11 @@
+export
+function w $main() {
+@start.1
+	%.1 =l alloc16 17
+	%.2 =l add %.1, 16
+	%.3 =l and %.2, 18446744073709551584
+@body.2
+	%.4 =l extsw 32
+	%.5 =l urem %.3, %.4
+	ret %.5
+}
-- 
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