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[LoopUnswitch] Remove BFI usage (dead code)

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Chandler mentioned at the last social that the need for BFI in the new pass manager was causing a slight hiccup for this pass.  Given this code has been checked in, but off for over a year, it makes sense to just remove it for now.

Note that there's nothing wrong with the general idea - it's actually a quite good one - and once we have the infrastructure in place to implement this without the full recompuation on every loop, we absolutely should.

llvm-svn: 294715
This commit is contained in:
Philip Reames 2017-02-10 06:12:06 +00:00
parent dd1f0a3f3a
commit 278a638de5
2 changed files with 0 additions and 95 deletions
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43
lib/Transforms/Scalar/LoopUnswitch.cpp
View File

@ -77,19 +77,6 @@ static cl::opt<unsigned>
Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
cl::init(100), cl::Hidden);
static cl::opt<bool>
LoopUnswitchWithBlockFrequency("loop-unswitch-with-block-frequency",
cl::init(false), cl::Hidden,
cl::desc("Enable the use of the block frequency analysis to access PGO "
"heuristics to minimize code growth in cold regions."));
static cl::opt<unsigned>
ColdnessThreshold("loop-unswitch-coldness-threshold", cl::init(1), cl::Hidden,
cl::desc("Coldness threshold in percentage. The loop header frequency "
"(relative to the entry frequency) is compared with this "
"threshold to determine if non-trivial unswitching should be "
"enabled."));
namespace {
class LUAnalysisCache {
@ -174,13 +161,6 @@ namespace {
LUAnalysisCache BranchesInfo;
bool EnabledPGO;
// BFI and ColdEntryFreq are only used when PGO and
// LoopUnswitchWithBlockFrequency are enabled.
BlockFrequencyInfo BFI;
BlockFrequency ColdEntryFreq;
bool OptimizeForSize;
bool redoLoop;
@ -457,19 +437,6 @@ bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
if (SanitizeMemory)
computeLoopSafetyInfo(&SafetyInfo, L);
EnabledPGO = F->getEntryCount().hasValue();
if (LoopUnswitchWithBlockFrequency && EnabledPGO) {
BranchProbabilityInfo BPI(*F, *LI);
BFI.calculate(*L->getHeader()->getParent(), BPI, *LI);
// Use BranchProbability to compute a minimum frequency based on
// function entry baseline frequency. Loops with headers below this
// frequency are considered as cold.
const BranchProbability ColdProb(ColdnessThreshold, 100);
ColdEntryFreq = BlockFrequency(BFI.getEntryFreq()) * ColdProb;
}
bool Changed = false;
do {
assert(currentLoop->isLCSSAForm(*DT));
@ -581,16 +548,6 @@ bool LoopUnswitch::processCurrentLoop() {
loopHeader->getParent()->hasFnAttribute(Attribute::OptimizeForSize))
return false;
if (LoopUnswitchWithBlockFrequency && EnabledPGO) {
// Compute the weighted frequency of the hottest block in the
// loop (loopHeader in this case since inner loops should be
// processed before outer loop). If it is less than ColdFrequency,
// we should not unswitch.
BlockFrequency LoopEntryFreq = BFI.getBlockFreq(loopHeader);
if (LoopEntryFreq < ColdEntryFreq)
return false;
}
for (IntrinsicInst *Guard : Guards) {
Value *LoopCond =
FindLIVLoopCondition(Guard->getOperand(0), currentLoop, Changed);

52
test/Transforms/LoopUnswitch/cold-loop.ll
View File

@ -1,52 +0,0 @@
; RUN: opt < %s -loop-unswitch -loop-unswitch-with-block-frequency -S 2>&1 | FileCheck %s
;; trivial condition should be unswithed regardless of coldness.
define i32 @test1(i1 %cond1, i1 %cond2) !prof !1 {
br i1 %cond1, label %loop_begin, label %loop_exit, !prof !0
loop_begin:
; CHECK: br i1 true, label %continue, label %loop_exit.loopexit
br i1 %cond2, label %continue, label %loop_exit ; trivial condition
continue:
call void @some_func1() noreturn nounwind
br label %loop_begin
loop_exit:
ret i32 0
}
;; cold non-trivial condition should not be unswitched.
define i32 @test2(i32* %var, i1 %cond1, i1 %cond2) !prof !1 {
br i1 %cond1, label %loop_begin, label %loop_exit, !prof !0
loop_begin:
store i32 1, i32* %var
; CHECK: br i1 %cond2, label %continue1, label %continue2
br i1 %cond2, label %continue1, label %continue2 ; non-trivial condition
continue1:
call void @some_func1() noreturn nounwind
br label %joint
continue2:
call void @some_func2() noreturn nounwind
br label %joint
joint:
;; unswitching will duplicate these calls.
call void @some_func3() noreturn nounwind
call void @some_func4() noreturn nounwind
br label %loop_begin
loop_exit:
ret i32 0
}
declare void @some_func1() noreturn
declare void @some_func2() noreturn
declare void @some_func3() noreturn
declare void @some_func4() noreturn
!0 = !{!"branch_weights", i32 1, i32 100000000}
!1 = !{!"function_entry_count", i64 100}