The compiler back-ends (i965's fs_visitor and brw_visitor,
ir_to_mesa_visitor, and glsl_to_tgsi_visitor) assume that when
ir_loop::counter is non-null, it points to a fresh ir_variable that
should be used as the loop counter (as opposed to an ir_variable that
exists elsewhere in the instruction stream).
However, previous to this patch:
(1) loop_control_visitor did not create a new variable for
ir_loop::counter; instead it re-used the existing ir_variable.
This caused the loop counter to be double-incremented (once
explicitly by the body of the loop, and once implicitly by
ir_loop::increment).
(2) ir_clone did not clone ir_loop::counter properly, resulting in the
cloned ir_loop pointing to the source ir_loop's counter.
(3) ir_hierarchical_visitor did not visit ir_loop::counter, resulting
in the ir_variable being missed by reparenting.
Additionally, most optimization passes (e.g. loop unrolling) assume
that the variable mentioned by ir_loop::counter is not accessed in the
body of the loop (an assumption which (1) violates).
The combination of these factors caused a perfect storm in which the
code worked properly nearly all of the time: for loops that got
unrolled, (1) would introduce a double-increment, but loop unrolling
would fail to notice it (since it assumes that ir_loop::counter is not
accessed in the body of the loop), so it would unroll the loop the
correct number of times. For loops that didn't get unrolled, (1)
would introduce a double-increment, but then later when the IR was
cloned for linking, (2) would prevent the loop counter from being
cloned properly, so it would look to further analysis stages like an
independent variable (and hence the double-increment would stop
occurring). At the end of linking, (3) would prevent the loop counter
from being reparented, so it would still belong to the shader object
rather than the linked program object. Provided that the client
program didn't delete the shader object, the memory would never get
reclaimed, and so the shader would function properly.
However, for loops that didn't get unrolled, if the client program did
delete the shader object, and the memory belonging to the loop counter
got re-used, this could cause a use-after-free bug, leading to a
crash.
This patch fixes loop_control_visitor, ir_clone, and
ir_hierarchical_visitor to treat ir_loop::counter the same way the
back-ends treat it: as a freshly allocated ir_variable that needs to
be visited and cloned independently of other ir_variables.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=72026
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
This gives the compiler the chance to inline and not export class symbols
even in the absence of LTO. Saves about 60kb on disk.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@.intel.com>
When analyzing a loop where the loop condition is expressed in the
non-standard order (e.g. "4 > i" instead of "i < 4"), we were
reversing the condition incorrectly, leading to a loop bound that was
off by 1.
Fixes piglit tests {vs,fs}-loop-bounds-unrolled.shader_test.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Fix the following GCC warning.
loop_controls.cpp: In function 'int calculate_iterations(ir_rvalue*, ir_rvalue*, ir_rvalue*, ir_expression_operation)':
loop_controls.cpp:88: warning: format not a string literal and no format arguments
The loop_controls pass didn't look at the counter values it put in ir_loop
on previous iterations, so while the first iteration worked, subsequent
ones couldn't determine max_iterations.
The places where constant_expression_value are still used in loop
analysis are places where a new expression tree is created and
constant folding won't have happened. This is used, for example, when
we try to determine the maximal loop iteration count.
Based on review comments by Eric. "...rely on constant folding to
have done its job, instead of going all through the subtree again when
it wasn't a constant."
