[SimplifyLibCalls] Don't confuse strcpy_chk for stpcpy_chk.

This was introduced in a faulty refactoring (r225640, mea culpa):
the tests weren't testing the return values, so, for both
__strcpy_chk and __stpcpy_chk, we would return the end of the
buffer (matching stpcpy) instead of the beginning (for strcpy).

The root cause was the prefix "__" being ignored when comparing,
which made us always pick LibFunc::stpcpy_chk.
Pass the LibFunc::Func directly to avoid this kind of error.
Also, make the testcases as explicit as possible to prevent this.

The now-useful testcases expose another, entangled, stpcpy problem,
with the further simplification.  This was introduced in a
refactoring (r225640) to match the original behavior.

However, this leads to problems when successive simplifications
generate several similar instructions, none of which are removed
by the custom replaceAllUsesWith.

For instance, InstCombine (the main user) doesn't erase the
instruction in its custom RAUW.  When trying to simplify say
__stpcpy_chk:
- first, an stpcpy is created (fortified simplifier),
- second, a memcpy is created (normal simplifier), but the
  stpcpy call isn't removed.
- third, InstCombine later revisits the instructions,
  and simplifies the first stpcpy to a memcpy.  We now have
  two memcpys.

llvm-svn: 227250

1 files changed, 14 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 13c2365e1ef..fb1d83fc333 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1968,8 +1968,12 @@ Value *LibCallSimplifier::optimizeCall(CallInst *CI) {
     // Try to further simplify the result.
     CallInst *SimplifiedCI = dyn_cast<CallInst>(SimplifiedFortifiedCI);
     if (SimplifiedCI && SimplifiedCI->getCalledFunction())
-      if (Value *V = optimizeStringMemoryLibCall(SimplifiedCI, Builder))
+      if (Value *V = optimizeStringMemoryLibCall(SimplifiedCI, Builder)) {
+        // If we were able to further simplify, remove the now redundant call.
+        SimplifiedCI->replaceAllUsesWith(V);
+        SimplifiedCI->eraseFromParent();
         return V;
+      }
     return SimplifiedFortifiedCI;
   }
 
@@ -2222,11 +2226,11 @@ Value *FortifiedLibCallSimplifier::optimizeMemSetChk(CallInst *CI, IRBuilder<> &
   return nullptr;
 }
 
-Value *FortifiedLibCallSimplifier::optimizeStrCpyChk(CallInst *CI, IRBuilder<> &B) {
+Value *FortifiedLibCallSimplifier::optimizeStrpCpyChk(CallInst *CI,
+                                                      IRBuilder<> &B,
+                                                      LibFunc::Func Func) {
   Function *Callee = CI->getCalledFunction();
   StringRef Name = Callee->getName();
-  LibFunc::Func Func =
-      Name.startswith("str") ? LibFunc::strcpy_chk : LibFunc::stpcpy_chk;
 
   if (!checkStringCopyLibFuncSignature(Callee, Func, DL))
     return nullptr;
@@ -2235,7 +2239,7 @@ Value *FortifiedLibCallSimplifier::optimizeStrCpyChk(CallInst *CI, IRBuilder<> &
         *ObjSize = CI->getArgOperand(2);
 
   // __stpcpy_chk(x,x,...)  -> x+strlen(x)
-  if (!OnlyLowerUnknownSize && Dst == Src) {
+  if (Func == LibFunc::stpcpy_chk && !OnlyLowerUnknownSize && Dst == Src) {
     Value *StrLen = EmitStrLen(Src, B, DL, TLI);
     return StrLen ? B.CreateInBoundsGEP(Dst, StrLen) : nullptr;
   }
@@ -2270,11 +2274,11 @@ Value *FortifiedLibCallSimplifier::optimizeStrCpyChk(CallInst *CI, IRBuilder<> &
   return nullptr;
 }
 
-Value *FortifiedLibCallSimplifier::optimizeStrNCpyChk(CallInst *CI, IRBuilder<> &B) {
+Value *FortifiedLibCallSimplifier::optimizeStrpNCpyChk(CallInst *CI,
+                                                       IRBuilder<> &B,
+                                                       LibFunc::Func Func) {
   Function *Callee = CI->getCalledFunction();
   StringRef Name = Callee->getName();
-  LibFunc::Func Func =
-      Name.startswith("str") ? LibFunc::strncpy_chk : LibFunc::stpncpy_chk;
 
   if (!checkStringCopyLibFuncSignature(Callee, Func, DL))
     return nullptr;
@@ -2314,10 +2318,10 @@ Value *FortifiedLibCallSimplifier::optimizeCall(CallInst *CI) {
     return optimizeMemSetChk(CI, Builder);
   case LibFunc::stpcpy_chk:
   case LibFunc::strcpy_chk:
-    return optimizeStrCpyChk(CI, Builder);
+    return optimizeStrpCpyChk(CI, Builder, Func);
   case LibFunc::stpncpy_chk:
   case LibFunc::strncpy_chk:
-    return optimizeStrNCpyChk(CI, Builder);
+    return optimizeStrpNCpyChk(CI, Builder, Func);
   default:
     break;
   }