5c: apply richard millers 5c-nan-cmp patch (from sources)

On ARM, it turns out that comparisons with NaN can be made to do the
right thing with no code penalty, by a more careful selection of
condition code values in the subsequent conditional branch.  The
meaning of the CC bits in the PSR is subtly different when they've
been copied from the floating point status register.

Suggested patch is 5c-nan-cmp (works on both vfp and emulated arm7500).

3 files changed, 17 insertions, 5 deletions

diff --git a/sys/src/cmd/5c/cgen.c b/sys/src/cmd/5c/cgen.c
index c639b180f..18971103b 100644
--- a/sys/src/cmd/5c/cgen.c
+++ b/sys/src/cmd/5c/cgen.c
@@ -701,7 +701,7 @@ boolgen(Node *n, int true, Node *nn)
 		if(true)
 			o = comrel[relindex(o)];
 		if(typefd[n->type->etype]) {
-			gopcode(o, nodfconst(0), &nod, Z);
+			gopcode(true ? o | BTRUE : o, nodfconst(0), &nod, Z);
 		} else
 			gopcode(o, nodconst(0), &nod, Z);
 		regfree(&nod);
@@ -800,14 +800,14 @@ boolgen(Node *n, int true, Node *nn)
 			regalloc(&nod, r, nn);
 			cgenrel(r, &nod, 1);
 			o = invrel[relindex(o)];
-			gopcode(o, l, &nod, Z);
+			gopcode(true ? o | BTRUE : o, l, &nod, Z);
 			regfree(&nod);
 			goto com;
 		}
 		if(sconst(r)) {
 			regalloc(&nod, l, nn);
 			cgenrel(l, &nod, 1);
-			gopcode(o, r, &nod, Z);
+			gopcode(true ? o | BTRUE : o, r, &nod, Z);
 			regfree(&nod);
 			goto com;
 		}
@@ -822,7 +822,7 @@ boolgen(Node *n, int true, Node *nn)
 			regalloc(&nod1, l, Z);
 			cgenrel(l, &nod1, 1);
 		}
-		gopcode(o, &nod, &nod1, Z);
+		gopcode(true ? o | BTRUE : o, &nod, &nod1, Z);
 		regfree(&nod);
 		regfree(&nod1);
 
diff --git a/sys/src/cmd/5c/gc.h b/sys/src/cmd/5c/gc.h
index e62955617..3d43b015c 100644
--- a/sys/src/cmd/5c/gc.h
+++ b/sys/src/cmd/5c/gc.h
@@ -14,6 +14,7 @@
 #define	SZ_VLONG	8
 #define	SZ_DOUBLE	8
 #define	FNX		100
+#define BTRUE		0x1000
 
 typedef	struct	Adr	Adr;
 typedef	struct	Prog	Prog;
diff --git a/sys/src/cmd/5c/txt.c b/sys/src/cmd/5c/txt.c
index 9ee8cb5b6..574694cdd 100644
--- a/sys/src/cmd/5c/txt.c
+++ b/sys/src/cmd/5c/txt.c
@@ -929,12 +929,14 @@ gins(int a, Node *f, Node *t)
 void
 gopcode(int o, Node *f1, Node *f2, Node *t)
 {
-	int a, et;
+	int a, et, true;
 	Adr ta;
 
 	et = TLONG;
 	if(f1 != Z && f1->type != T)
 		et = f1->type->etype;
+	true = o & BTRUE;
+	o &= ~BTRUE;
 	a = AGOK;
 	switch(o) {
 	case OAS:
@@ -1076,15 +1078,24 @@ gopcode(int o, Node *f1, Node *f2, Node *t)
 			break;
 		case OLT:
 			a = ABLT;
+			/* ensure NaN comparison is always false */
+			if(typefd[et] && !true)
+				a = ABMI;
 			break;
 		case OLE:
 			a = ABLE;
+			if(typefd[et] && !true)
+				a = ABLS;
 			break;
 		case OGE:
 			a = ABGE;
+			if(typefd[et] && true)
+				a = ABPL;
 			break;
 		case OGT:
 			a = ABGT;
+			if(typefd[et] && true)
+				a = ABHI;
 			break;
 		case OLO:
 			a = ABLO;