r600/sb: fix crash in fold_alu_op3

fold_assoc() called from fold_alu_op3() can lower the number of src to 2,
which then leads to an invalid access to n.src[2]->gvalue().
This didn't seem to have caused much harm in the past, but on Fedora 28
it will crash (presumably because -D_GLIBCXX_ASSERTIONS is used, although
with libstdc++ 4.8.5 this didn't do anything, -D_GLIBCXX_DEBUG was
needed to show the issue).

An alternative fix would be to instead call fold_alu_op2() from within
fold_assoc() when the number of src is reduced and return always TRUE
from fold_assoc() in this case, with the only actual difference being
the return value from fold_alu_op3() then. I'm not sure what the return
value actually should be in this case (or whether it even can make a
difference).

https://bugs.freedesktop.org/show_bug.cgi?id=106928
Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Dave Airlie <airlied@redhat.com>

diff --git a/src/gallium/drivers/r600/sb/sb_expr.cpp b/src/gallium/drivers/r600/sb/sb_expr.cpp
index 1df78da6608343cc0cf32a7642b4b4ed0b8483c1..ad798453bc1cf70a1f6faf684d3aee7a25f7f3d7 100644 (file)
--- a/src/gallium/drivers/r600/sb/sb_expr.cpp
+++ b/src/gallium/drivers/r600/sb/sb_expr.cpp
@@ -945,6 +945,8 @@ bool expr_handler::fold_alu_op3(alu_node& n) {
        if (!sh.safe_math && (n.bc.op_ptr->flags & AF_M_ASSOC)) {
                if (fold_assoc(&n))
                        return true;
+               if (n.src.size() < 3)
+                       return fold_alu_op2(n);
        }
 
        value* v0 = n.src[0]->gvalue();