Add loop distribution to the LTO pipeline

The LoopDistribute pass is missing from the LTO pipeline, so
-enable-loop-distribute has no effect during post-link. The pre-link
loop distribution doesn't seem to survive the LTO pipeline either.

With this patch (and -flto -mllvm -enable-loop-distribute) we see a 43%
uplift on SPEC 2006 hmmer for AArch64. The rest of SPECINT 2006 is
unaffected.

Differential Revision: https://reviews.llvm.org/D89896

llvm/lib/Transforms/IPO/PassManagerBuilder.cpp

@@ -1055,6 +1055,7 @@ void PassManagerBuilder::addLTOOptimizationPasses(legacy::PassManagerBase &PM) {
   // Unroll small loops
   PM.add(createSimpleLoopUnrollPass(OptLevel, DisableUnrollLoops,
                                     ForgetAllSCEVInLoopUnroll));
+  PM.add(createLoopDistributePass());
   PM.add(createLoopVectorizePass(true, !LoopVectorize));
   // The vectorizer may have significantly shortened a loop body; unroll again.
   PM.add(createLoopUnrollPass(OptLevel, DisableUnrollLoops,

llvm/test/Other/opt-LTO-pipeline.ll

@@ -128,9 +128,17 @@
 ; CHECK-NEXT:         Induction Variable Simplification
 ; CHECK-NEXT:         Delete dead loops
 ; CHECK-NEXT:         Unroll loops
+; CHECK-NEXT:       Loop Access Analysis
+; CHECK-NEXT:       Lazy Branch Probability Analysis
+; CHECK-NEXT:       Lazy Block Frequency Analysis
+; CHECK-NEXT:       Optimization Remark Emitter
+; CHECK-NEXT:       Loop Distribution
 ; CHECK-NEXT:       Post-Dominator Tree Construction
 ; CHECK-NEXT:       Branch Probability Analysis
 ; CHECK-NEXT:       Block Frequency Analysis
+; CHECK-NEXT:       Scalar Evolution Analysis
+; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:       Function Alias Analysis Results
 ; CHECK-NEXT:       Loop Access Analysis
 ; CHECK-NEXT:       Demanded bits analysis
 ; CHECK-NEXT:       Lazy Branch Probability Analysis