shithub: riscv

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ref: 52dc943702a8f7815546e76286b153c3813e1db0
parent: 5bc9b0c3cac34864d479c099283793ec4ae5565e
author: Ori Bernstein <ori@eigenstate.org>
date: Sun Mar 15 11:08:04 EDT 2020

fix ccom idempotency

ccom may be called multiple times on the same
node, via 'goto loop' calls from the commute
label, OADD, and a few other places.

Casts to void could null out the LHS of the
node, which would cause the compiler to crash
if the cast was revisited due to one of these
cases, because we tried frobbing n->left.

Now, if n->left is nil, we just return.w

--- a/sys/src/cmd/cc/com.c

+++ b/sys/src/cmd/cc/com.c

@@ -1018,6 +1018,8 @@

  *	remove some zero operands

  *	remove no op casts

  *	evaluate constants

+ * Note: ccom may be called on the same node

+ * multiple times.

  */

 void

 ccom(Node *n)

@@ -1078,8 +1080,9 @@

 		if(n->type == types[TVOID] && !side(l)){

 			n->left = Z;

 			n->type = T;

-			break;

 		}

+		if(n->left == Z)

+			break;

 		if(castucom(n))

 			warn(n, "32-bit unsigned complement zero-extended to 64 bits");

 		ccom(l);