In try_to_simplify_bb(), simplification is attempted when a constant phisrc whose corresponding phi-node control a conditional branch. In this case, for the path between the phisrc and the conditional branch, the following OP_PHI is sort of unneeded since the constant determine which branch will be taken. If this simplification can be made, it means that the OP_PHI doesn't depend anymore on the constant phisrc. In fact the OP_PHI's bb won't be anymore reachable from the constant phisrc's bb. But currently, the OP_PHI usage is not adjusted and this leads to all sort of oddities and causes to miss further simplifications. The situation can be more concretly seen on test-linearize's output, here an extract of Linux's kernel/futex.c:get_futex_key(). .L594: ... br %r1294, .L651, .L656 .L651: phisrc.32 %phi85 <- $1 br .L649 .L656: ... and.64 %r1340 <- %r1339, $1 phisrc.32 %phi87 <- %r1340 phi.32 %r1343 <- %phi85, %phi87 br %r1343, .L649, .L648 The constant phisrc is %phi85 in .L651, the OP_PHI and the conditional branch are .L656's last instructions (which have been packed with its now unique parent which is sign of a problem). One can see that the OP_PHi seems to depend on %phi85 (it's in its phi_list) but in fact depends only on %phi87 (.L656 can't be reached from .L651 where %phi85 is defined since after the simplification .L651 directly branches to one of the .L656's children, here .L649). The fix consists in adjusting the OP_PHI's usage when the simplification is made. On the same code extract we can now see that the situation is more "normal". In fact the OP_PHI have now been able to be optimized away together, as well as .L651: .L594: ... br %r1294, .L649, .L656 .L656: ... and.64 %r1340 <- %r1339, $1 br %r1340, .L649, .L648 Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> Signed-off-by: Christopher Li <sparse@chrisli.org>