revert r311333: [LibCallSimplifier] try harder to fold memcmp with constant arguments

We're getting lots of compile-timeout bot failures like:
http://lab.llvm.org:8011/builders/clang-native-arm-lnt/builds/7119
http://lab.llvm.org:8011/builders/clang-cmake-x86_64-avx2-linux

llvm-svn: 311340

1 files changed, 10 insertions, 26 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index b2319945a2c..8257dbcf858 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -18,7 +18,6 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/Triple.h"
-#include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/OptimizationDiagnosticInfo.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
@@ -752,44 +751,29 @@ Value *LibCallSimplifier::optimizeMemCmp(CallInst *CI, IRBuilder<> &B) {
   }
 
   // memcmp(S1,S2,N/8)==0 -> (*(intN_t*)S1 != *(intN_t*)S2)==0
-  // TODO: The case where both inputs are constants does not need to be limited
-  // to legal integers or equality comparison. See block below this.
   if (DL.isLegalInteger(Len * 8) && isOnlyUsedInZeroEqualityComparison(CI)) {
+
     IntegerType *IntType = IntegerType::get(CI->getContext(), Len * 8);
     unsigned PrefAlignment = DL.getPrefTypeAlignment(IntType);
 
-    // First, see if we can fold either argument to a constant.
-    Value *LHSV = nullptr;
-    if (auto *LHSC = dyn_cast<Constant>(LHS)) {
-      LHSC = ConstantExpr::getBitCast(LHSC, IntType->getPointerTo());
-      LHSV = ConstantFoldLoadFromConstPtr(LHSC, IntType, DL);
-    }
-    Value *RHSV = nullptr;
-    if (auto *RHSC = dyn_cast<Constant>(RHS)) {
-      RHSC = ConstantExpr::getBitCast(RHSC, IntType->getPointerTo());
-      RHSV = ConstantFoldLoadFromConstPtr(RHSC, IntType, DL);
-    }
+    if (getKnownAlignment(LHS, DL, CI) >= PrefAlignment &&
+        getKnownAlignment(RHS, DL, CI) >= PrefAlignment) {
 
-    // Don't generate unaligned loads. If either source is constant data,
-    // alignment doesn't matter for that source because there is no load.
-    if (!LHSV && getKnownAlignment(LHS, DL, CI) >= PrefAlignment) {
       Type *LHSPtrTy =
           IntType->getPointerTo(LHS->getType()->getPointerAddressSpace());
-      LHSV = B.CreateLoad(B.CreateBitCast(LHS, LHSPtrTy), "lhsv");
-    }
-
-    if (!RHSV && getKnownAlignment(RHS, DL, CI) >= PrefAlignment) {
       Type *RHSPtrTy =
           IntType->getPointerTo(RHS->getType()->getPointerAddressSpace());
-      RHSV = B.CreateLoad(B.CreateBitCast(RHS, RHSPtrTy), "rhsv");
-    }
 
-    if (LHSV && RHSV)
+      Value *LHSV =
+          B.CreateLoad(B.CreateBitCast(LHS, LHSPtrTy, "lhsc"), "lhsv");
+      Value *RHSV =
+          B.CreateLoad(B.CreateBitCast(RHS, RHSPtrTy, "rhsc"), "rhsv");
+
       return B.CreateZExt(B.CreateICmpNE(LHSV, RHSV), CI->getType(), "memcmp");
+    }
   }
 
-  // Constant folding: memcmp(x, y, Len) -> constant (all arguments are const).
-  // TODO: This is limited to i8 arrays.
+  // Constant folding: memcmp(x, y, l) -> cnst (all arguments are constant)
   StringRef LHSStr, RHSStr;
   if (getConstantStringInfo(LHS, LHSStr) &&
       getConstantStringInfo(RHS, RHSStr)) {