x86_64/isel: fix edge case with branch on float add result

In `if (x + 1)` the implicit `!= 0` can be omitted for integers, because
the x86 `add` instruction sets the zero flag accordingly. But for floats
it doesn't, so applying that optimization there was wrong. Luckily it
was caught by a nullptr dereference later in `emit::Xjcc()` for the
(missing) unordered branch target, instead of miscompiling.

2 files changed, 6 insertions, 1 deletions

diff --git a/test/12-flt.c b/test/12-flt.c
index 36f4e90..5077026 100644
--- a/test/12-flt.c
+++ b/test/12-flt.c
@@ -40,6 +40,11 @@ double nummod(double a, double b) {
    return m;
 }
 
+double branch(double a) {
+   if (a + 1.1) return 0.0;
+   return -a;
+}
+
 int main() {
    NAN/=0.0;
    assert(_(1.0) < _(2.0));
diff --git a/x86_64/isel.c b/x86_64/isel.c
index 3a753e6..ded1a52 100644
--- a/x86_64/isel.c
+++ b/x86_64/isel.c
@@ -577,7 +577,7 @@ seljmp(struct function *fn, struct block *blk)
        && (oiscmp(instrtab[c.i].op) || instrtab[c.i].op == Oand || instrtab[c.i].op == Osub)) {
          instrtab[c.i].keep = 1;
       } else {
-         if (!(opflags[instrtab[c.i].op] & ZF) || blk->ins.n == 0 || c.i != blk->ins.p[blk->ins.n - 1]) {
+         if (kisflt(instrtab[c.i].cls) || !(opflags[instrtab[c.i].op] & ZF) || blk->ins.n == 0 || c.i != blk->ins.p[blk->ins.n - 1]) {
             struct instr *ins;
             int curi = blk->ins.n;
             blk->jmp.arg[0] = insertinstr(blk, blk->ins.n, mkinstr(Oneq, insrescls(instrtab[c.i]), c, ZEROREF));