[LoopUnroll] Don't verify domtree by default with +Asserts.

This verification is linear in the size of the function, so it can cause
a quadratic compile-time explosion in a function with many loops to
unroll.

Differential Revision: https://reviews.llvm.org/D54732

llvm-svn: 349871

llvm/lib/Transforms/Utils/LoopUnroll.cpp

@@ -54,10 +54,10 @@ UnrollRuntimeEpilog("unroll-runtime-epilog", cl::init(false), cl::Hidden,
 static cl::opt<bool>
 UnrollVerifyDomtree("unroll-verify-domtree", cl::Hidden,
                     cl::desc("Verify domtree after unrolling"),
-#ifdef NDEBUG
-    cl::init(false)
-#else
+#ifdef EXPENSIVE_CHECKS
     cl::init(true)
+#else
+    cl::init(false)
 #endif
                     );
 

llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp

@@ -615,7 +615,9 @@ bool llvm::peelLoop(Loop *L, unsigned PeelCount, LoopInfo *LI,
       // the original loop body.
       if (Iter == 0)
         DT->changeImmediateDominator(Exit, cast<BasicBlock>(LVMap[Latch]));
+#ifdef EXPENSIVE_CHECKS
       assert(DT->verify(DominatorTree::VerificationLevel::Fast));
+#endif
     }
 
     auto *LatchBRCopy = cast<BranchInst>(VMap[LatchBR]);