[ExpandMemCmp] Split ExpandMemCmp from CodeGen into its own pass.

Summary:
This is mostly a noop (most of the test diffs are renamed blocks).
There are a few temporary register renames (eax<->ecx) and a few blocks are
shuffled around.

See the discussion in PR33325 for more details.

Reviewers: spatel

Subscribers: mgorny

Differential Revision: https://reviews.llvm.org/D39456

llvm-svn: 317211

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/TargetPassConfig.cpp b/llvm/lib/CodeGen/TargetPassConfig.cpp
index c5101b1ecfc..59e88ba3bda 100644
--- a/llvm/lib/CodeGen/TargetPassConfig.cpp
+++ b/llvm/lib/CodeGen/TargetPassConfig.cpp
@@ -600,8 +600,14 @@ void TargetPassConfig::addIRPasses() {
       addPass(createPrintFunctionPass(dbgs(), "\n\n*** Code after LSR ***\n"));
   }
 
-  if (getOptLevel() != CodeGenOpt::None && EnableMergeICmps) {
-    addPass(createMergeICmpsPass());
+  if (getOptLevel() != CodeGenOpt::None) {
+    // The MergeICmpsPass tries to create memcmp calls by grouping sequences of
+    // loads and compares. ExpandMemCmpPass then tries to expand those calls
+    // into optimally-sized loads and compares. The transforms are enabled by a
+    // target lowering hook.
+    if (EnableMergeICmps)
+      addPass(createMergeICmpsPass());
+    addPass(createExpandMemCmpPass());
   }
 
   // Run GC lowering passes for builtin collectors