5l: two stack split bugs in one day

An ARM expert could probably phrase the
comparison in fewer instructions, but this works.

R=ken2
CC=golang-dev
https://golang.org/cl/2620041

diff --git a/src/cmd/5l/noop.c b/src/cmd/5l/noop.c
index a3a0ae29b25b3afe462d3970debad882d54e093e..5def0d3f1693c265223827acbf53e5ce81c058de 100644 (file)
--- a/src/cmd/5l/noop.c
+++ b/src/cmd/5l/noop.c
@@ -37,6 +37,7 @@
 enum
 {
        StackBig = 4096,
+       StackSmall = 128,
 };
 
 static Sym*    sym_div;
@@ -296,7 +297,7 @@ noops(void)
                                        // TODO(kaib): add more trampolines
                                        // TODO(kaib): put stackguard in register
                                        // TODO(kaib): add support for -K and underflow detection
-       
+
                                        // MOVW                 g_stackguard(g), R1
                                        p = appendp(p);
                                        p->as = AMOVW;
@@ -304,14 +305,31 @@ noops(void)
                                        p->from.reg = REGG;
                                        p->to.type = D_REG;
                                        p->to.reg = 1;
-       
-                                       // CMP                  R1, $-autosize(SP)
-                                       p = appendp(p);
-                                       p->as = ACMP;
-                                       p->from.type = D_REG;
-                                       p->from.reg = 1;
-                                       p->from.offset = -autosize;
-                                       p->reg = REGSP;
+                                       
+                                       if(autosize < StackSmall) {     
+                                               // CMP                  R1, SP
+                                               p = appendp(p);
+                                               p->as = ACMP;
+                                               p->from.type = D_REG;
+                                               p->from.reg = 1;
+                                               p->reg = REGSP;
+                                       } else {
+                                               // MOVW         $-autosize(SP), R2
+                                               // CMP  R1, R2
+                                               p = appendp(p);
+                                               p->as = AMOVW;
+                                               p->from.type = D_CONST;
+                                               p->from.reg = REGSP;
+                                               p->from.offset = -autosize;
+                                               p->to.type = D_REG;
+                                               p->to.reg = 2;
+                                               
+                                               p = appendp(p);
+                                               p->as = ACMP;
+                                               p->from.type = D_REG;
+                                               p->from.reg = 1;
+                                               p->reg = 2;
+                                       }
        
                                        // MOVW.LO              $autosize, R1
                                        p = appendp(p);