[CompileTime] [Passes] Avoid computing unnecessary analyses. NFC

Similar to c515b2f, If there are no loops in the function as seen through LI, we should avoid computing the remaining expensive analyses (such as SCEV, BPI). Reordered the analyses requests and early return if there are no loops. The logic of avoiding expensive analyses is applied to LoopVectorizer, LoopLoadElimination and LoopUnrollPass, i.e. all function passes which operate on loops. This is an NFC with compile time improvement. Differential Revision: https://reviews.llvm.org/D124529
llvm · Apr 29, 2022 · 205246c · 205246c
1 parent f685bce
commit 205246c
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Showing 4 changed files with 16 additions and 6 deletions.
diff --git a/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp b/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
@@ -706,8 +706,12 @@ FunctionPass *llvm::createLoopLoadEliminationPass() {
 
 PreservedAnalyses LoopLoadEliminationPass::run(Function &F,
                                                FunctionAnalysisManager &AM) {
-  auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
   auto &LI = AM.getResult<LoopAnalysis>(F);
+  // There are no loops in the function. Return before computing other expensive
+  // analyses.
+  if (LI.empty())
+    return PreservedAnalyses::all();
+  auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
   auto &TTI = AM.getResult<TargetIRAnalysis>(F);
   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);

diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -1545,8 +1545,12 @@ PreservedAnalyses LoopFullUnrollPass::run(Loop &L, LoopAnalysisManager &AM,
 
 PreservedAnalyses LoopUnrollPass::run(Function &F,
                                       FunctionAnalysisManager &AM) {
-  auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
   auto &LI = AM.getResult<LoopAnalysis>(F);
+  // There are no loops in the function. Return before computing other expensive
+  // analyses.
+  if (LI.empty())
+    return PreservedAnalyses::all();
+  auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
   auto &TTI = AM.getResult<TargetIRAnalysis>(F);
   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
   auto &AC = AM.getResult<AssumptionAnalysis>(F);

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -10732,8 +10732,12 @@ LoopVectorizeResult LoopVectorizePass::runImpl(
 
 PreservedAnalyses LoopVectorizePass::run(Function &F,
                                          FunctionAnalysisManager &AM) {
-    auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
     auto &LI = AM.getResult<LoopAnalysis>(F);
+    // There are no loops in the function. Return before computing other expensive
+    // analyses.
+    if (LI.empty())
+      return PreservedAnalyses::all();
+    auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
     auto &TTI = AM.getResult<TargetIRAnalysis>(F);
     auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
     auto &BFI = AM.getResult<BlockFrequencyAnalysis>(F);

diff --git a/llvm/test/Transforms/SCCP/preserve-analysis.ll b/llvm/test/Transforms/SCCP/preserve-analysis.ll
@@ -5,10 +5,8 @@
 
 ; NEW-PM-DAG: Running analysis: LoopAnalysis on test
 ; NEW-PM-DAG: Running analysis: DominatorTreeAnalysis on test
-; NEW-PM-DAG: Running analysis: AssumptionAnalysis on test
-; NEW-PM-DAG: Running analysis: TargetLibraryAnalysis on test
-; NEW-PM-DAG: Running analysis: TargetIRAnalysis on test
 ; NEW-PM: Running pass: SCCPPass on test
+; NEW-PM: Running analysis: TargetLibraryAnalysis on test
 ; NEW-PM-NOT: Running analysis: LoopAnalysis on test
 ; NEW-PM-NOT: Running analysis: DominatorTreeAnalysis on test
 ; NEW-PM-NOT: Running analysis: AssumptionAnalysis on test