From 41b3c7a50727f715111d09af982e2e9a0deeb688 Mon Sep 17 00:00:00 2001
From: James Lyon <jamesly0n@hotmail.com>
Date: Sat, 27 Apr 2013 20:39:34 +0100
Subject: Improved variable length array support.

VLA storage is now freed when it goes out of scope. This makes it
possible to use a VLA inside a loop without consuming an unlimited
amount of memory.

Combining VLAs with alloca() should work as in GCC - when a VLA is
freed, memory allocated by alloca() after the VLA was created is also
freed. There are some exceptions to this rule when using goto: if a VLA
is in scope at the goto, jumping to a label will reset the stack pointer
to where it was immediately after the last VLA was created prior to the
label, or to what it was before the first VLA was created if the label
is outside the scope of any VLA. This means that in some cases combining
alloca() and VLAs will free alloca() memory where GCC would not.
---
 i386-gen.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

(limited to 'i386-gen.c')

diff --git a/i386-gen.c b/i386-gen.c
index 044f9e6..9ff2e18 100644
--- a/i386-gen.c
+++ b/i386-gen.c
@@ -43,6 +43,7 @@ enum {
     TREG_ECX,
     TREG_EDX,
     TREG_ST0,
+    TREG_ESP = 4
 };
 
 /* return registers for function */
@@ -1117,6 +1118,44 @@ ST_FUNC void gen_bounded_ptr_deref(void)
 }
 #endif
 
+/* Save the stack pointer onto the stack */
+ST_FUNC void gen_vla_sp_save(int addr) {
+    /* mov %esp,addr(%ebp)*/
+    o(0x89);
+    gen_modrm(TREG_ESP, VT_LOCAL, NULL, addr);
+}
+
+/* Restore the SP from a location on the stack */
+ST_FUNC void gen_vla_sp_restore(int addr) {
+    o(0x8b);
+    gen_modrm(TREG_ESP, VT_LOCAL, NULL, addr);
+}
+
+/* Subtract from the stack pointer, and push the resulting value onto the stack */
+ST_FUNC void gen_vla_alloc(CType *type, int align) {
+#ifdef TCC_TARGET_PE
+    /* alloca does more than just adjust %rsp on Windows */
+    vpush_global_sym(&func_old_type, TOK_alloca);
+    vswap(); /* Move alloca ref past allocation size */
+    gfunc_call(1);
+    vset(type, REG_IRET, 0);
+#else
+    int r;
+    r = gv(RC_INT); /* allocation size */
+    /* sub r,%rsp */
+    o(0x2b);
+    o(0xe0 | r);
+    /* We align to 16 bytes rather than align */
+    /* and ~15, %esp */
+    o(0xf0e483);
+    /* mov %esp, r */
+    o(0x89);
+    o(0xe0 | r);
+    vpop();
+    vset(type, r, 0);
+#endif
+}
+
 /* end of X86 code generator */
 /*************************************************************/
 #endif
-- 
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