From 8bbcd0e3e67882c314ee478e6be563b1bb178c26 Mon Sep 17 00:00:00 2001
From: Philip Reames <listmail@philipreames.com>
Date: Fri, 10 Feb 2017 06:12:06 +0000
Subject: [PATCH] [LoopUnswitch] Remove BFI usage (dead code)

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.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294715 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopUnswitch.cpp    | 43 -------------------
 test/Transforms/LoopUnswitch/cold-loop.ll | 52 -----------------------
 2 files changed, 95 deletions(-)
 delete mode 100644 test/Transforms/LoopUnswitch/cold-loop.ll

diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp
index d7daab4c666..d42119df3dc 100644
--- a/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -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);
diff --git a/test/Transforms/LoopUnswitch/cold-loop.ll b/test/Transforms/LoopUnswitch/cold-loop.ll
deleted file mode 100644
index 1fbc08038bb..00000000000
--- a/test/Transforms/LoopUnswitch/cold-loop.ll
+++ /dev/null
@@ -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}
-- 
2.50.1