[InstCombine] Optimize some memccpy calls to memcpy/null

Summary:
return memccpy(d, "helloworld", 'r', 20)
=>
return memcpy(d, "helloworld", 8 /* pos of 'r' in string */), d + 8

Reviewers: efriedma, jdoerfert

Reviewed By: jdoerfert

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68089

1 files changed, 41 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 18a17119b47..6d1def357bd 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1119,6 +1119,45 @@ Value *LibCallSimplifier::optimizeMemCpy(CallInst *CI, IRBuilder<> &B) {
   return CI->getArgOperand(0);
 }
 
+Value *LibCallSimplifier::optimizeMemCCpy(CallInst *CI, IRBuilder<> &B) {
+  Value *Dst = CI->getArgOperand(0);
+  Value *Src = CI->getArgOperand(1);
+  ConstantInt *StopChar = dyn_cast<ConstantInt>(CI->getArgOperand(2));
+  ConstantInt *N = dyn_cast<ConstantInt>(CI->getArgOperand(3));
+  StringRef SrcStr;
+  if (CI->use_empty() && Dst == Src)
+    return Dst;
+  // memccpy(d, s, c, 0) -> nullptr
+  if (N) {
+    if (N->isNullValue())
+      return Constant::getNullValue(CI->getType());
+    if (!getConstantStringInfo(Src, SrcStr, /*Offset=*/0,
+                               /*TrimAtNul=*/false) ||
+        !StopChar)
+      return nullptr;
+  } else {
+    return nullptr;
+  }
+
+  // Wrap arg 'c' of type int to char
+  size_t Pos = SrcStr.find(StopChar->getSExtValue() & 0xFF);
+  if (Pos == StringRef::npos) {
+    if (N->getZExtValue() <= SrcStr.size()) {
+      B.CreateMemCpy(Dst, 1, Src, 1, CI->getArgOperand(3));
+      return Constant::getNullValue(CI->getType());
+    }
+    return nullptr;
+  }
+
+  Value *NewN =
+      ConstantInt::get(N->getType(), std::min(Pos + 1, N->getZExtValue()));
+  // memccpy -> llvm.memcpy
+  B.CreateMemCpy(Dst, 1, Src, 1, NewN);
+  return Pos + 1 <= N->getZExtValue()
+             ? B.CreateInBoundsGEP(B.getInt8Ty(), Dst, NewN)
+             : Constant::getNullValue(CI->getType());
+}
+
 Value *LibCallSimplifier::optimizeMemPCpy(CallInst *CI, IRBuilder<> &B) {
   Value *Dst = CI->getArgOperand(0);
   Value *N = CI->getArgOperand(2);
@@ -2864,6 +2903,8 @@ Value *LibCallSimplifier::optimizeStringMemoryLibCall(CallInst *CI,
       return optimizeMemCmp(CI, Builder);
     case LibFunc_memcpy:
       return optimizeMemCpy(CI, Builder);
+    case LibFunc_memccpy:
+      return optimizeMemCCpy(CI, Builder);
     case LibFunc_mempcpy:
       return optimizeMemPCpy(CI, Builder);
     case LibFunc_memmove: