Fix issue with overloaded subscript and ++/--.

test/test_suite/methods/operator_inc.c3t

@@ -0,0 +1,65 @@
+// #target: macos-x64
+module test;
+
+import std;
+
+struct Foo
+{
+	int[5] a;
+}
+fn int Foo.get(self, usz i) @operator([]) => self.a[i];
+fn void Foo.set(&self, usz i, int j) @operator([]=) { self.a[i] = j; }
+
+Foo m;
+fn void main() {
+
+	m.a[3] = 100;
+	int x = m[3]--;
+}
+
+/* #expect: test.ll
+
+define i32 @test.Foo.get(ptr byval(%Foo) align 8 %0, i64 %1) #0 {
+entry:
+  %ptroffset = getelementptr inbounds [4 x i8], ptr %0, i64 %1
+  %2 = load i32, ptr %ptroffset, align 4
+  ret i32 %2
+}
+
+define void @test.Foo.set(ptr %0, i64 %1, i32 %2) #0 {
+entry:
+  %ptroffset = getelementptr inbounds [4 x i8], ptr %0, i64 %1
+  store i32 %2, ptr %ptroffset, align 4
+  ret void
+}
+
+define void @test.main() #0 {
+entry:
+  %x = alloca i32, align 4
+  %.anon = alloca ptr, align 8
+  %.anon1 = alloca i32, align 4
+  %.anon2 = alloca i32, align 4
+  %indirectarg = alloca %Foo, align 8
+  %.anon3 = alloca i32, align 4
+  store i32 100, ptr getelementptr inbounds (i8, ptr @test.m, i64 12), align 4
+  store ptr @test.m, ptr %.anon, align 8
+  store i32 3, ptr %.anon1, align 4
+  %0 = load ptr, ptr %.anon, align 8
+  %1 = load i32, ptr %.anon1, align 4
+  %sext = sext i32 %1 to i64
+  call void @llvm.memcpy.p0.p0.i32(ptr align 8 %indirectarg, ptr align 4 %0, i32 20, i1 false)
+  %2 = call i32 @test.Foo.get(ptr byval(%Foo) align 8 %indirectarg, i64 %sext)
+  store i32 %2, ptr %.anon2, align 4
+  %3 = load i32, ptr %.anon2, align 4
+  %sub = sub i32 %3, 1
+  store i32 %sub, ptr %.anon2, align 4
+  store i32 %3, ptr %.anon3, align 4
+  %4 = load i32, ptr %.anon1, align 4
+  %sext4 = sext i32 %4 to i64
+  %5 = load ptr, ptr %.anon, align 8
+  %6 = load i32, ptr %.anon2, align 4
+  call void @test.Foo.set(ptr %5, i64 %sext4, i32 %6)
+  %7 = load i32, ptr %.anon3, align 4
+  store i32 %7, ptr %x, align 4
+  ret void
+}