amd64: fix conditional jump when compare is swapped and used elsewhere

selcmp may potentially swap the arguments and return 1 indicating
that the opposite operation should be used. However, if the compare
result is used for a conditional jump as well as elsewhere, the
original compare op is used instead of the opposite.

To fix this, add a check to see whether the opposite compare should
be used, regardless of whether selcmp() is done now, or later on
during sel().

Bug report and test case from Charlie Stanton.

1 files changed, 17 insertions, 0 deletions

diff --git a/test/cmp1.ssa b/test/cmp1.ssa
new file mode 100644
index 0000000..dd5bfa1
--- /dev/null
+++ b/test/cmp1.ssa
@@ -0,0 +1,17 @@
+# test cmp used in jnz as well as its result value
+
+export
+function w $test(w %c) {
+@start
+	%cmp =w cultw 1, %c
+	jnz %cmp, @yes, @no
+@yes
+	%cmp =w copy 1
+@no
+	ret %cmp
+}
+
+# >>> driver
+# int test(int);
+# int main(void) { return test(0); }
+# <<<