Author: meinersbur
Date: Wed Dec 12 09:32:52 2018
New Revision: 348944
URL: http://llvm.org/viewvc/llvm-project?rev=348944&view=rev
Log:
[Unroll/UnrollAndJam/Vectorizer/Distribute] Add followup loop attributes.
When multiple loop transformation are defined in a loop's metadata, their order
of execution is defined by the order of their respective passes in the pass
pipeline. For instance, e.g.
#pragma clang loop unroll_and_jam(enable)
#pragma clang loop distribute(enable)
is the same as
#pragma clang loop distribute(enable)
#pragma clang loop unroll_and_jam(enable)
and will try to loop-distribute before Unroll-And-Jam because the
LoopDistribute pass is scheduled after UnrollAndJam pass. UnrollAndJamPass only
supports one inner loop, i.e. it will necessarily fail after loop distribution.
It is not possible to specify another execution order. Also,t the order of
passes in the pipeline is subject to change between versions of LLVM,
optimization options and which pass manager is used.
This patch adds 'followup' attributes to various loop transformation passes.
These attributes define which attributes the resulting loop of a transformation
should have. For instance,
!0 = !{!0, !1, !2}
!1 = !{!"llvm.loop.unroll_and_jam.enable"}
!2 = !{!"llvm.loop.unroll_and_jam.followup_inner", !3}
!3 = !{!"llvm.loop.distribute.enable"}
defines a loop ID (!0) to be unrolled-and-jammed (!1) and then the attribute !3
to be added to the jammed inner loop, which contains the instruction to
distribute the inner loop.
Currently, in both pass managers, pass execution is in a fixed order and
UnrollAndJamPass will not execute again after LoopDistribute. We hope to fix
this in the future by allowing pass managers to run passes until a fixpoint is
reached, use Polly to perform these transformations, or add a loop
transformation pass which takes the order issue into account.
For mandatory/forced transformations (e.g. by having been declared by #pragma
omp simd), the user must be notified when a transformation could not be
performed. It is not possible that the responsible pass emits such a warning
because the transformation might be 'hidden' in a followup attribute when it is
executed, or it is not present in the pipeline at all. For this reason, this
patche introduces a WarnMissedTransformations pass, to warn about orphaned
transformations.
Since this changes the user-visible diagnostic message when a transformation is
applied, two test cases in the clang repository need to be updated.
To ensure that no other transformation is executed before the intended one, the
attribute `llvm.loop.disable_nonforced` can be added which should disable
transformation heuristics before the intended transformation is applied. E.g.
it would be surprising if a loop is distributed before a #pragma unroll_and_jam
is applied.
With more supported code transformations (loop fusion, interchange,
stripmining, offloading, etc.), transformations can be used as building blocks
for more complex transformations (e.g. stripmining+stripmining+interchange ->
tiling).
Reviewed By: hfinkel, dmgreen
Differential Revision: https://reviews.llvm.org/D49281
Differential Revision: https://reviews.llvm.org/D55288
Modified:
cfe/trunk/test/Misc/backend-optimization-failure-nodbg.cpp
cfe/trunk/test/Misc/backend-optimization-failure.cpp
Modified: cfe/trunk/test/Misc/backend-optimization-failure-nodbg.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Misc/backend-optimization-failure-nodbg.cpp?rev=348944&r1=348943&r2=348944&view=diff
==============================================================================
--- cfe/trunk/test/Misc/backend-optimization-failure-nodbg.cpp (original)
+++ cfe/trunk/test/Misc/backend-optimization-failure-nodbg.cpp Wed Dec 12
09:32:52 2018
@@ -4,7 +4,7 @@
// Test verifies optimization failures generated by the backend are handled
// correctly by clang. LLVM tests verify all of the failure conditions.
-void test_switch(int *A, int *B, int Length, int J) { /* expected-warning
{{loop not vectorized: failed explicitly specified loop vectorization}} */
+void test_switch(int *A, int *B, int Length, int J) { /* expected-warning
{{loop not vectorized: the optimizer was unable to perform the requested
transformation; the transformation might be disabled or specified as part of an
unsupported transformation ordering}} */
#pragma clang loop vectorize(enable) unroll(disable)
for (int i = 0; i < Length; i++) {
switch (A[i]) {
Modified: cfe/trunk/test/Misc/backend-optimization-failure.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Misc/backend-optimization-failure.cpp?rev=348944&r1=348943&r2=348944&view=diff
==============================================================================
--- cfe/trunk/test/Misc/backend-optimization-failure.cpp (original)
+++ cfe/trunk/test/Misc/backend-optimization-failure.cpp Wed Dec 12 09:32:52
2018
@@ -7,7 +7,7 @@
void test_switch(int *A, int *B, int Length,int J) {
#pragma clang loop vectorize(enable) unroll(disable)
for (int i = 0; i < Length; i++) {
-/* expected-warning@-1 {{loop not vectorized: failed explicitly specified loop
vectorization}} */ switch (A[i]) {
+/* expected-warning@-1 {{loop not vectorized: the optimizer was unable to
perform the requested transformation; the transformation might be disabled or
specified as part of an unsupported transformation ordering}} */ switch (A[i]) {
case 0:
B[i] = 1;
break;
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