[LPM/BPI] Preserve BPI through trivial loop pass pipeline (e.g. LCSSA, LoopSimplify)

Currently, we do not expose BPI to loop passes at all. In the old pass manager, we appear to have been ignoring the fact that LCSSA and/or LoopSimplify didn't preserve BPI, and making it available to the following loop passes anyways.  In the new one, it's invalidated before running any loop pass if either LCSSA or LoopSimplify actually make changes. If they don't make changes, then BPI is valid and available.  So, we go ahead and teach LCSSA and LoopSimplify how to preserve BPI for consistency between old and new pass managers.

This patch avoids an invalidation between the two requires in the following trivial pass pipeline:
opt -passes="requires<branch-prob>,loop(no-op-loop),requires<branch-prob>"
(when the input file is one which requires either LCSSA or LoopSimplify to canonicalize the loops)

Differential Revision: https://reviews.llvm.org/D60790

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358901 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/LCSSA.cpp b/lib/Transforms/Utils/LCSSA.cpp
index 73b2e4326c481743b2f27077101c556ad9cb126a..5ddb7381a56896f0902c14a6eaa08bc1438e8f81 100644 (file)
--- a/lib/Transforms/Utils/LCSSA.cpp
+++ b/lib/Transforms/Utils/LCSSA.cpp
@@ -31,6 +31,7 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/BasicAliasAnalysis.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/ScalarEvolution.h"
@@ -442,6 +443,7 @@ struct LCSSAWrapperPass : public FunctionPass {
     AU.addPreserved<GlobalsAAWrapperPass>();
     AU.addPreserved<ScalarEvolutionWrapperPass>();
     AU.addPreserved<SCEVAAWrapperPass>();
+    AU.addPreserved<BranchProbabilityInfoWrapperPass>();
 
     // This is needed to perform LCSSA verification inside LPPassManager
     AU.addRequired<LCSSAVerificationPass>();
@@ -485,5 +487,8 @@ PreservedAnalyses LCSSAPass::run(Function &F, FunctionAnalysisManager &AM) {
   PA.preserve<GlobalsAA>();
   PA.preserve<SCEVAA>();
   PA.preserve<ScalarEvolutionAnalysis>();
+  // BPI maps terminators to probabilities, since we don't modify the CFG, no
+  // updates are needed to preserve it.
+  PA.preserve<BranchProbabilityAnalysis>();
   return PA;
 }

diff --git a/lib/Transforms/Utils/LoopSimplify.cpp b/lib/Transforms/Utils/LoopSimplify.cpp
index c347b5e26e3830bd376c124735a8383ea30b0bd8..b076e6ffc5320aab83aea963653692da33eb819b 100644 (file)
--- a/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/lib/Transforms/Utils/LoopSimplify.cpp
@@ -48,6 +48,7 @@
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/BasicAliasAnalysis.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/DependenceAnalysis.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/InstructionSimplify.h"
@@ -740,6 +741,7 @@ namespace {
       AU.addPreservedID(LCSSAID);
       AU.addPreserved<DependenceAnalysisWrapperPass>();
       AU.addPreservedID(BreakCriticalEdgesID);  // No critical edges added.
+      AU.addPreserved<BranchProbabilityInfoWrapperPass>();
     }
 
     /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
@@ -812,6 +814,12 @@ PreservedAnalyses LoopSimplifyPass::run(Function &F,
   PA.preserve<SCEVAA>();
   PA.preserve<ScalarEvolutionAnalysis>();
   PA.preserve<DependenceAnalysis>();
+  // BPI maps conditional terminators to probabilities, LoopSimplify can insert
+  // blocks, but it does so only by splitting existing blocks and edges. This
+  // results in the interesting property that all new terminators inserted are
+  // unconditional branches which do not appear in BPI. All deletions are
+  // handled via ValueHandle callbacks w/in BPI. 
+  PA.preserve<BranchProbabilityAnalysis>();
   return PA;
 }
 

diff --git a/test/Other/opt-O2-pipeline.ll b/test/Other/opt-O2-pipeline.ll
index ca12d9ad6635ed5aa9f021909f5cf05b02c7a470..12999c64026f67cd07672a20b0e0e28b10886169 100644 (file)
--- a/test/Other/opt-O2-pipeline.ll
+++ b/test/Other/opt-O2-pipeline.ll
@@ -271,7 +271,6 @@
 ; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:       Function Alias Analysis Results
 ; CHECK-NEXT:       Scalar Evolution Analysis
-; CHECK-NEXT:       Branch Probability Analysis
 ; CHECK-NEXT:       Block Frequency Analysis
 ; CHECK-NEXT:       Loop Pass Manager
 ; CHECK-NEXT:         Loop Sink

diff --git a/test/Other/opt-O3-pipeline.ll b/test/Other/opt-O3-pipeline.ll
index 864b748df1bf706d6f879507633c72c08a064194..366a138203866f0c4f1e7447605d10830f51b77d 100644 (file)
--- a/test/Other/opt-O3-pipeline.ll
+++ b/test/Other/opt-O3-pipeline.ll
@@ -276,7 +276,6 @@
 ; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:       Function Alias Analysis Results
 ; CHECK-NEXT:       Scalar Evolution Analysis
-; CHECK-NEXT:       Branch Probability Analysis
 ; CHECK-NEXT:       Block Frequency Analysis
 ; CHECK-NEXT:       Loop Pass Manager
 ; CHECK-NEXT:         Loop Sink

diff --git a/test/Other/opt-Os-pipeline.ll b/test/Other/opt-Os-pipeline.ll
index a0240ac2977aef56fa83a6aa65752bdbc7a0bf1c..c3a225d5e8d7ebb71dbd6c768892dab974546468 100644 (file)
--- a/test/Other/opt-Os-pipeline.ll
+++ b/test/Other/opt-Os-pipeline.ll
@@ -258,7 +258,6 @@
 ; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:       Function Alias Analysis Results
 ; CHECK-NEXT:       Scalar Evolution Analysis
-; CHECK-NEXT:       Branch Probability Analysis
 ; CHECK-NEXT:       Block Frequency Analysis
 ; CHECK-NEXT:       Loop Pass Manager
 ; CHECK-NEXT:         Loop Sink