more codegen

notes.md

@@ -0,0 +1,69 @@
+# lowering
+
+This C program
+
+```c
+long main() {
+    long a = 0;
+    int b = 0;
+    return 0;
+}
+```
+
+should lower into the following unoptimized IR
+
+```llvmir
+def main() {
+  bb0:
+    %a = alloca, size=8, align=8
+    store %a, 0, size=8, align=8
+    %b = alloca, size=4, align=4
+    store %b, 0, size=4, align=4
+    ret 0
+}
+```
+
+this IR can then be lowered to very sane machine code ignoring stack alignment which also like matters
+
+```x86asm
+sub rbp, 8    ; a
+mov [rbp], 0
+sub rbp, 4    ; b
+xor rax, rax
+ret
+```
+
+---
+
+```c
+int main()
+{
+    int a = 1 + 3 * 4;
+    return 0;
+}
+```
+
+```llvmir
+def main() {
+  bb0:
+    %a = alloca, size=4, align=4
+    %1 = mul 3, 4
+    %2 = add 1, %1
+    store %a, %2, size=4, align=4
+    ret 0
+}
+```
+
+```x86asm
+sub rbp, 4  ; a
+sub rbp, 4  ; %1
+mov rbx, 3
+mul rbx, 4
+mov dword ptr [rbp], rbx
+sub rbp, 4  ; %2
+mov rbx, 1
+add rbx, dword ptr [rbp + 4]
+mov dword ptr [rbp + 8], dword ptr [rbp]
+xor rax, rax
+ret
+```