[MergeICmps] MergeICmps is a new optimization pass that turns chains of integer

comparisons into memcmp.

Thanks to recent improvements in the LLVM codegen, the memcmp is typically
inlined as a chain of efficient hardware comparisons.
This typically benefits C++ member or nonmember operator==().

For now this is disabled by default until:
 - https://bugs.llvm.org/show_bug.cgi?id=33329 is complete
 - Benchmarks show that this is always useful.

Differential Revision:
https://reviews.llvm.org/D33987

llvm-svn: 312315

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TargetPassConfig.cpp b/llvm/lib/CodeGen/TargetPassConfig.cpp
index 481baea2dff..329768769f1 100644
--- a/llvm/lib/CodeGen/TargetPassConfig.cpp
+++ b/llvm/lib/CodeGen/TargetPassConfig.cpp
@@ -94,6 +94,10 @@ static cl::opt<bool> EnableImplicitNullChecks(
     "enable-implicit-null-checks",
     cl::desc("Fold null checks into faulting memory operations"),
     cl::init(false));
+static cl::opt<bool> EnableMergeICmps(
+    "enable-mergeicmps",
+    cl::desc("Merge ICmp chains into a single memcmp"),
+    cl::init(false));
 static cl::opt<bool> PrintLSR("print-lsr-output", cl::Hidden,
     cl::desc("Print LLVM IR produced by the loop-reduce pass"));
 static cl::opt<bool> PrintISelInput("print-isel-input", cl::Hidden,
@@ -591,6 +595,10 @@ void TargetPassConfig::addIRPasses() {
       addPass(createPrintFunctionPass(dbgs(), "\n\n*** Code after LSR ***\n"));
   }
 
+  if (getOptLevel() != CodeGenOpt::None && EnableMergeICmps) {
+    addPass(createMergeICmpsPass());
+  }
+
   // Run GC lowering passes for builtin collectors
   // TODO: add a pass insertion point here
   addPass(createGCLoweringPass());