for P1, optimize short branches forward to the return label

Author: totalspectrum

backends/asm/assemble_ir.c

@@ -945,13 +945,6 @@ PrintCompressCondJump(struct flexbuf *fb, int cond, Operand *dst)
     flexbuf_addstr(fb, "\n");
 }
 
-// LMM jumps +- this amount are turned into add/sub of the pc
-// pick a conservative value
-// 127 would be the absolute maximum here
-#define MAX_REL_JUMP_OFFSET_LMM 100
-// On P2 conditional jumps have a range +/- 256
-#define MAX_REL_JUMP_OFFSET_P2 200
-
 /* convert IR list into assembly language */
 static int didPub = 0;
 
@@ -1230,10 +1223,14 @@ DoAssembleIR(struct flexbuf *fb, IR *ir, Module *P)
                 PrintCond(fb, ir->cond);
                 // if we know the destination we may be able to optimize
                 // the branch
-                if (ir->aux && gl_lmm_kind == LMM_KIND_ORIG && !(ir->flags & (FLAG_KEEP_INSTR|FLAG_JMPTABLE_INSTR))) {
+                if ((ir->flags & FLAG_RET_BRANCH) || (ir->aux && gl_lmm_kind == LMM_KIND_ORIG && !(ir->flags & (FLAG_KEEP_INSTR|FLAG_JMPTABLE_INSTR))) ) {
                     int offset;
-                    dest = (IR *)ir->aux;
-                    offset = dest->addr - ir->addr;
+                    if (ir->aux) {
+                        dest = (IR *)ir->aux;
+                        offset = dest->addr - ir->addr;
+                    } else {
+                        offset = 1; /* fake, but we know it's a short forward branch */
+                    }
                     if ( offset > 0 && offset < MAX_REL_JUMP_OFFSET_LMM) {
                         flexbuf_printf(fb, "add\t__pc, #4*(");
                         PrintOperand(fb, ir->dst);

backends/asm/optimize_ir.c

@@ -3307,7 +3307,7 @@ OptimizeAddSub(IRList *irl)
 // forward or backward
 //
 static void
-AssignTemporaryAddresses(IRList *irl)
+AssignTemporaryAddresses(IRList *irl, Operand *retlabel)
 {
     IR *ir;
     unsigned addr = 0;
@@ -3323,6 +3323,16 @@ AssignTemporaryAddresses(IRList *irl)
             ir->aux = NULL;
         }
     }
+    /* on P1, flag short branches to the return */
+    if (retlabel && !gl_p2) {
+        for (ir = irl->head; ir; ir = ir->next) {
+            if (IsJump(ir) && ir->dst == retlabel
+                && (addr - ir->addr < MAX_REL_JUMP_OFFSET_LMM))
+            {
+                ir->flags |= FLAG_RET_BRANCH;
+            }
+        }
+    }
 }
 
 //
@@ -5348,7 +5358,7 @@ OptimizeIRLocal(IRList *irl, Function *f)
 again:
     do {
         change = 0;
-        AssignTemporaryAddresses(irl);
+        AssignTemporaryAddresses(irl, FuncData(f)->asmreturnlabel);
         if (flags & OPT_BASIC_REGS) {
             OPT_PASS(CheckLabelUsage(irl));
             OPT_PASS(OptimizeReadWrite(irl));

backends/asm/outasm.h

@@ -1,6 +1,6 @@
 /*
  * Spin to Pasm converter
- * Copyright 2016-2024 Total Spectrum Software Inc.
+ * Copyright 2016-2025 Total Spectrum Software Inc.
  * PASM output routines
  */
 
@@ -11,6 +11,13 @@
 #include "becommon.h"
 #include "util/sha256.h"
 
+// LMM jumps +- this amount are turned into add/sub of the pc
+// pick a conservative value
+// 127 would be the absolute maximum here
+#define MAX_REL_JUMP_OFFSET_LMM 100
+// On P2 conditional jumps have a range +/- 256
+#define MAX_REL_JUMP_OFFSET_P2 200
+
 // functions for producing local identifiers
 const char *IdentifierLocalName(Function *func, const char *name);
 const char *IdentifierModuleName(Module *P, const char *name);

instr.h

@@ -295,8 +295,9 @@ enum flags {
     FLAG_USER_FCACHE     = 0x20000,
 
     // rest of the bits are used by the optimizer
-    FLAG_LABEL_USED = 0x100000,
-    FLAG_INSTR_NEW  = 0x200000,
+    FLAG_LABEL_USED =  0x100000,
+    FLAG_INSTR_NEW  =  0x200000,
+    FLAG_RET_BRANCH =  0x400000,  /* for a short forward branch to return */
     FLAG_OPTIMIZER = 0xFFF00000,
 };