[AArch64] Re-run load/store optimizer after aggressive tail duplication

The Load/Store Optimizer runs before Machine Block Placement. At O3 the
Tail Duplication Threshold is set to 4 instructions and this can create
new opportunities for the Load/Store Optimizer. It seems worthwhile to
run it once again.

llvm-svn: 349338

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
index d5e24708ece..32c853483e3 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -556,6 +556,12 @@ void AArch64PassConfig::addPreSched2() {
 }
 
 void AArch64PassConfig::addPreEmitPass() {
+  // Machine Block Placement might have created new opportunities when run
+  // at O3, where the Tail Duplication Threshold is set to 4 instructions.
+  // Run the load/store optimizer once more.
+  if (TM->getOptLevel() >= CodeGenOpt::Aggressive && EnableLoadStoreOpt)
+    addPass(createAArch64LoadStoreOptimizationPass());
+
   if (EnableA53Fix835769)
     addPass(createAArch64A53Fix835769());
   // Relax conditional branch instructions if they're otherwise out of