Summary:
We need to use floating-point compares to ensure that s_cbranch_vcc*
instructions are always generated. With integer compares, future
optimizations could cause s_cbranch_scc* to be generated instead.
Reviewers: arsenm, nhaehnle
Subscribers: llvm-commits, kzhuravl
Differential Revision: https://reviews.llvm.org/D23401
llvm-svn: 279148
If a loop is not rotated (for example when optimizing for size), the latch is not the backedge. If we promote an expression to post-inc form, we not only increase register pressure and add a COPY for that IV expression but for all IVs!
Motivating testcase:
void f(float *a, float *b, float *c, int n) {
while (n-- > 0)
*c++ = *a++ + *b++;
}
It's imperative that the pointer increments be located in the latch block and not the header block; if not, we cannot use post-increment loads and stores and we have to keep both the post-inc and pre-inc values around until the end of the latch which bloats register usage.
llvm-svn: 278658
Insert before the skip branch if one is created.
This is a somewhat more natural placement relative
to the skip branches, and makes it possible to implement
analyzeBranch for skip blocks.
The test changes are mostly due to a quirk where
the block label is not emitted if there is a terminator
that is not also a branch.
llvm-svn: 278273
Summary:
Two types of stores are possible in pixel shaders: stores to memory that are
explicitly requested at the API level, and stores that are an implementation
detail of register spilling or lowering of arrays.
For the first kind of store, we must ensure that helper pixels have no effect
and hence WQM must be disabled. The second kind of store must always be
executed, because the written value may be loaded again in a way that is
relevant for helper pixels as well -- and there are no externally visible
effects anyway.
This is a candidate for the 3.9 release branch.
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: arsenm, kzhuravl, llvm-commits
Differential Revision: https://reviews.llvm.org/D22675
llvm-svn: 277504
Summary:
There are cases where uniform branch conditions are computed in VGPRs, and
we didn't correctly mark those as WQM.
The stray change in basic-branch.ll is because invoking the LiveIntervals
analysis leads to the detection of a dead register that would otherwise not
be seen at -O0.
This is a candidate for the 3.9 branch, as it fixes a possible hang.
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: arsenm, llvm-commits, kzhuravl
Differential Revision: https://reviews.llvm.org/D22673
llvm-svn: 277500
The main sin this was committing was using terminator
instructions in the middle of the block, and then
not updating the block successors / predecessors.
Split the blocks up to avoid this and introduce new
pseudo instructions for branches taken with exec masking.
Also use a pseudo instead of emitting s_endpgm and erasing
it in the special case of a non-void return.
llvm-svn: 273467
Summary:
The presence of this attribute indicates that VGPR outputs should be computed
in whole quad mode. This will be used by Mesa for prolog pixel shaders, so
that derivatives can be taken of shader inputs computed by the prolog, fixing
a bug.
The generated code could certainly be improved: if a prolog pixel shader is
used (which isn't common in modern OpenGL - they're used for gl_Color, polygon
stipples, and forcing per-sample interpolation), Mesa will use this attribute
unconditionally, because it has to be conservative. So WQM may be used in the
prolog when it isn't really needed, and furthermore a silly back-and-forth
switch is likely to happen at the boundary between prolog and main shader
parts.
Fixing this is a bit involved: we'd first have to add a mechanism by which
LLVM writes the WQM-related input requirements to the main shader part binary,
and then Mesa specializes the prolog part accordingly. At that point, we may
as well just compile a monolithic shader...
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95130
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: arsenm, llvm-commits, kzhuravl
Differential Revision: http://reviews.llvm.org/D20839
llvm-svn: 272063
Allocating larger register classes first should give better allocation
results (and more importantly for myself, make the lit tests more stable
with respect to scheduler changes).
Patch by Matthias Braun
llvm-svn: 270312
This makes it possible to distinguish between mesa shaders
and other kernels even in the presence of compute shaders.
Patch By: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Differential Revision: http://reviews.llvm.org/D18559
llvm-svn: 265589
Summary:
Whole quad mode is already enabled for pixel shaders that compute
derivatives, but it must be suspended for instructions that cause a
shader to have side effects (i.e. stores and atomics).
This pass addresses the issue by storing the real (initial) live mask
in a register, masking EXEC before instructions that require exact
execution and (re-)enabling WQM where required.
This pass is run before register coalescing so that we can use
machine SSA for analysis.
The changes in this patch expose a problem with the second machine
scheduling pass: target independent instructions like COPY implicitly
use EXEC when they operate on VGPRs, but this fact is not encoded in
the MIR. This can lead to miscompilation because instructions are
moved past changes to EXEC.
This patch fixes the problem by adding use-implicit operands to
target independent instructions. Some general codegen passes are
relaxed to work with such implicit use operands.
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: MatzeB, arsenm, llvm-commits
Differential Revision: http://reviews.llvm.org/D18162
llvm-svn: 263982
Tom Stellard