Make func_800C213C match original ROM (#678)

* Make func_800C213C match original ROM

The C code for this function was very close to done, and was
functionally equivalent to the ROM.  This commit uses a few tricks
to convince the compiler to allocate the same registers as the original
ROM.  The two tricks used are:
1. Introduced a new temporary variable "yinc".
2. Added a "do while(0) {}" line in two places.

Both of these ideas came from the decomp-permuter tool.  I took the
do/while idea and guess as to what it might have been in the original
code.  I imagined that the "do while(0) {}" was probably left over from
a standard multi-line macro, which for some reason had an empty body.
I further suggest that maybe the empty body is because it was a feature
compiled out during RELEASE builds - perhaps a debug logging macro.

* Use simpler code for func_800C213C

Replaced dummy LOG macro with "do {} while(0);".  This version makes
less assumptions about what the original code looked like.

1 files changed, 8 insertions, 9 deletions

diff --git a/src/code/PreRender.c b/src/code/PreRender.c
index 94afbafb7..bc65fe3a0 100644
--- a/src/code/PreRender.c
+++ b/src/code/PreRender.c
@@ -308,14 +308,13 @@ void func_800C2118(PreRenderContext* this, Gfx** gfxp) {
     func_800C0F28(this, gfxp, this->zbufSave, this->zbuf);
 }
 
-#ifdef NON_MATCHING
-// regalloc differences in gDPLoadMultiTile
 void func_800C213C(PreRenderContext* this, Gfx** gfxp) {
     Gfx* gfx;
     s32 y;
     s32 y2;
     s32 add;
     s32 uls;
+    s32 yinc;  // vertical increment amount
     s32 ult;
     s32 lrx;
     s32 lry;
@@ -350,20 +349,23 @@ void func_800C213C(PreRenderContext* this, Gfx** gfxp) {
         }
 
         uls = 0;
+        yinc = 1;
         ult = y2;
-        lry = (y2 + add - 1);
+        lry = (y2 + add - yinc);
 
         gDPLoadMultiTile(gfx++, this->fbufSave, 0x0000, G_TX_RENDERTILE, G_IM_FMT_RGBA, G_IM_SIZ_16b, this->width,
                          this->height, uls, ult, lrx, lry, 0, G_TX_NOMIRROR | G_TX_WRAP, G_TX_NOMIRROR | G_TX_WRAP,
                          G_TX_NOMASK, G_TX_NOMASK, G_TX_NOLOD, G_TX_NOLOD);
-        gDPLoadMultiTile(gfx++, this->cvgSave, 0x0160, 1, G_IM_FMT_I, G_IM_SIZ_8b, this->width, this->height, uls, ult,
+
+        do {} while(0);  // force register allocation behavior
+        gDPLoadMultiTile(gfx++, this->cvgSave, 0x0160, yinc, G_IM_FMT_I, G_IM_SIZ_8b, this->width, this->height, uls, ult,
                          lrx, lry, 0, G_TX_NOMIRROR | G_TX_WRAP, G_TX_NOMIRROR | G_TX_WRAP, G_TX_NOMASK, G_TX_NOMASK,
                          G_TX_NOLOD, G_TX_NOLOD);
 
-        gSPTextureRectangle(gfx++, uls << 2, ult << 2, (lrx + 1) << 2, (lry + 1) << 2, G_TX_RENDERTILE, uls << 5,
+        do {} while(0);  // force register allocation behavior
+        gSPTextureRectangle(gfx++, uls << 2, ult << 2, (lrx + yinc) << 2, (lry + yinc) << 2, G_TX_RENDERTILE, uls << 5,
                             ult << 5, 1 << 10, 1 << 10);
 
-        if (1) {}
         y -= add;
         y2 += add;
     }
@@ -371,9 +373,6 @@ void func_800C213C(PreRenderContext* this, Gfx** gfxp) {
     gDPPipeSync(gfx++);
     *gfxp = gfx;
 }
-#else
-#pragma GLOBAL_ASM("asm/non_matchings/code/PreRender/func_800C213C.s")
-#endif
 
 void func_800C24BC(PreRenderContext* this, Gfx** gfxp) {
     func_800C0F28(this, gfxp, this->fbufSave, this->fbuf);