shithub: mc

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Take into account subregisters when coalescing.

    This fixes a bug we may potentially hit in register allocation
    when we have a different size register we want to coalesce. Eg:

        movb %P.117,%P.118
        xorl %rax,%rax
        movb %P.118,%al

    This change prevents coalescing %al with a clobbered register.

--- a/6/ra.c

+++ b/6/ra.c

@@ -763,6 +763,18 @@

     }

 }

+static int constrained(Isel *s, regid u, regid v)

+{

+    size_t i;

+

+    if (bshas(s->prepainted, v))

+        return 1;

+    if (bshas(s->prepainted, u))

+        for (i = 0; i < Nmode; i++)

+            if (regmap[colourmap[u]][i] && gbhasedge(s, regmap[colourmap[u]][i], v))

+                return 1;

+    return gbhasedge(s, u, v);

+}

 static void coalesce(Isel *s)

 {

     Insn *m;

@@ -782,7 +794,7 @@

         lappend(&s->mcoalesced, &s->nmcoalesced, m);

         wladd(s, u);

         wladd(s, v);

-    } else if (bshas(s->prepainted, v) || gbhasedge(s, u, v)) {

+    } else if (constrained(s, u, v)) {

         lappend(&s->mconstrained, &s->nmconstrained, m);

         wladd(s, u);

         wladd(s, v);

@@ -879,7 +891,7 @@

 }

 /*

- * Selects the colors for registers, spilling to the

+ * Selects the colours for registers, spilling to the

  * stack if no free registers can be found.

  */

 static int paint(Isel *s)