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[IRCE] Avoid loop optimizations on pre and post loops

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Summary:
This patch will add loop metadata on the pre and post loops generated by IRCE.
Currently, we have metadata for disabling optimizations such as vectorization,
unrolling, loop distribution and LICM versioning (and confirmed that these
optimizations check for the metadata before proceeding with the transformation).

The pre and post loops generated by IRCE need not go through loop opts (since
these are slow paths).

Added two test cases as well.

Reviewers: sanjoy, reames

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D26806

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@289588 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Anna Thomas 2016-12-13 21:05:21 +00:00
parent d2b07a0d57
commit a740af8f6f
2 changed files with 115 additions and 0 deletions
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34
lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
View File

@ -399,6 +399,34 @@ void InductiveRangeCheck::extractRangeChecksFromBranch(
Checks, Visited);
}
// Add metadata to the loop L to disable loop optimizations. Callers need to
// confirm that optimizing loop L is not beneficial.
static void DisableAllLoopOptsOnLoop(Loop &L) {
// We do not care about any existing loopID related metadata for L, since we
// are setting all loop metadata to false.
LLVMContext &Context = L.getHeader()->getContext();
// Reserve first location for self reference to the LoopID metadata node.
MDNode *Dummy = MDNode::get(Context, {});
MDNode *DisableUnroll = MDNode::get(
Context, {MDString::get(Context, "llvm.loop.unroll.disable")});
Metadata *FalseVal =
ConstantAsMetadata::get(ConstantInt::get(Type::getInt1Ty(Context), 0));
MDNode *DisableVectorize = MDNode::get(
Context,
{MDString::get(Context, "llvm.loop.vectorize.enable"), FalseVal});
MDNode *DisableLICMVersioning = MDNode::get(
Context, {MDString::get(Context, "llvm.loop.licm_versioning.disable")});
MDNode *DisableDistribution= MDNode::get(
Context,
{MDString::get(Context, "llvm.loop.distribute.enable"), FalseVal});
MDNode *NewLoopID =
MDNode::get(Context, {Dummy, DisableUnroll, DisableVectorize,
DisableLICMVersioning, DisableDistribution});
// Set operand 0 to refer to the loop id itself.
NewLoopID->replaceOperandWith(0, NewLoopID);
L.setLoopID(NewLoopID);
}
namespace {
// Keeps track of the structure of a loop. This is similar to llvm::Loop,
@ -1309,6 +1337,9 @@ bool LoopConstrainer::run() {
&OriginalLoop, OriginalLoop.getParentLoop(), PreLoop.Map);
formLCSSARecursively(*L, DT, &LI, &SE);
simplifyLoop(L, &DT, &LI, &SE, nullptr, true);
// Pre loops are slow paths, we do not need to perform any loop
// optimizations on them.
DisableAllLoopOptsOnLoop(*L);
}
if (!PostLoop.Blocks.empty()) {
@ -1316,6 +1347,9 @@ bool LoopConstrainer::run() {
&OriginalLoop, OriginalLoop.getParentLoop(), PostLoop.Map);
formLCSSARecursively(*L, DT, &LI, &SE);
simplifyLoop(L, &DT, &LI, &SE, nullptr, true);
// Post loops are slow paths, we do not need to perform any loop
// optimizations on them.
DisableAllLoopOptsOnLoop(*L);
}
formLCSSARecursively(OriginalLoop, DT, &LI, &SE);

81
test/Transforms/IRCE/add-metadata-pre-post-loops.ll Normal file
View File

@ -0,0 +1,81 @@
; RUN: opt -irce -S < %s 2>&1 | FileCheck %s
; test that the pre and post loops have loop metadata which disables any further
; loop optimizations.
; generates a post loop, which should have metadata !llvm.loop !2
; Function Attrs: alwaysinline
define void @inner_loop(i32* %arr, i32* %a_len_ptr, i32 %n) #0 {
; CHECK-LABEL: inner_loop(
; CHECK-LABEL: in.bounds.postloop
; CHECK: br i1 %next.postloop, label %loop.postloop, label %exit.loopexit.loopexit, !llvm.loop !2, !irce.loop.clone !7
entry:
%len = load i32, i32* %a_len_ptr, !range !0
%first.itr.check = icmp sgt i32 %n, 0
br i1 %first.itr.check, label %loop, label %exit
loop: ; preds = %in.bounds, %entry
%idx = phi i32 [ 0, %entry ], [ %idx.next, %in.bounds ]
%idx.next = add i32 %idx, 1
%abc = icmp slt i32 %idx, %len
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds: ; preds = %loop
%addr = getelementptr i32, i32* %arr, i32 %idx
store i32 0, i32* %addr
%next = icmp slt i32 %idx.next, %n
br i1 %next, label %loop, label %exit
out.of.bounds: ; preds = %loop
ret void
exit: ; preds = %in.bounds, %entry
ret void
}
; add loop metadata for pre and post loops
define void @single_access_with_preloop(i32 *%arr, i32 *%a_len_ptr, i32 %n, i32 %offset) {
; CHECK-LABEL: @single_access_with_preloop(
; CHECK-LABEL: in.bounds.preloop
; CHECK: br i1 %14, label %loop.preloop, label %preloop.exit.selector, !llvm.loop !8, !irce.loop.clone !7
; CHECK-LABEL: in.bounds.postloop
; CHECK: br i1 %next.postloop, label %loop.postloop, label %exit.loopexit.loopexit, !llvm.loop !9, !irce.loop.clone !7
entry:
%len = load i32, i32* %a_len_ptr, !range !0
%first.itr.check = icmp sgt i32 %n, 0
br i1 %first.itr.check, label %loop, label %exit
loop:
%idx = phi i32 [ 0, %entry ] , [ %idx.next, %in.bounds ]
%idx.next = add i32 %idx, 1
%array.idx = add i32 %idx, %offset
%abc.high = icmp slt i32 %array.idx, %len
%abc.low = icmp sge i32 %array.idx, 0
%abc = and i1 %abc.low, %abc.high
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds:
%addr = getelementptr i32, i32* %arr, i32 %array.idx
store i32 0, i32* %addr
%next = icmp slt i32 %idx.next, %n
br i1 %next, label %loop, label %exit
out.of.bounds:
ret void
exit:
ret void
}
attributes #0 = { alwaysinline }
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 64, i32 4}
!2 = distinct !{!2, !3, !4, !5, !6}
!3 = !{!"llvm.loop.unroll.disable"}
!4 = !{!"llvm.loop.vectorize.enable", i1 false}
!5 = !{!"llvm.loop.licm_versioning.disable"}
!6 = !{!"llvm.loop.distribute.enable", i1 false}
!7 = !{}
!8 = distinct !{!8, !3, !4, !5}
!9 = distinct !{!9, !3, !4, !5}