[PATCH] D106769: [MemCpyOpt] Relax libcall checks

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
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Rather than blocking the whole MemCpyOpt pass if the libcalls are not available, only disable creation of new memset/memcpy intrinsics where none existed previously. This only affects the store merging and load-store conversion optimization. Other optimizations are derived from existing intrinsics, which are well-defined in the absence of libcalls -- not having the libcalls just means that call simplification won't convert them to intrinsics.

This is a weaker variation of D104801 <https://reviews.llvm.org/D104801>, which dropped these checks entirely.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106769

Files:
  llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp


Index: llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -673,7 +673,10 @@
         LI->getParent() == SI->getParent()) {
 
       auto *T = LI->getType();
-      if (T->isAggregateType()) {
+      // Don't introduce calls to memcpy/memmove intrinsics out of thin air if
+      // the corresponding libcalls are not available.
+      if (T->isAggregateType() && TLI->has(LibFunc_memcpy) &&
+          TLI->has(LibFunc_memmove)) {
         MemoryLocation LoadLoc = MemoryLocation::get(LI);
 
         // We use alias analysis to check if an instruction may store to
@@ -796,6 +799,11 @@
     }
   }
 
+  // The following code creates memset intrinsics out of thin air. Don't do
+  // this if the corresponding libfunc is not available.
+  if (!TLI->has(LibFunc_memset))
+    return false;
+
   // There are two cases that are interesting for this code to handle: memcpy
   // and memset.  Right now we only handle memset.
 
@@ -1548,9 +1556,6 @@
 /// Transforms memmove calls to memcpy calls when the src/dst are guaranteed
 /// not to alias.
 bool MemCpyOptPass::processMemMove(MemMoveInst *M) {
-  if (!TLI->has(LibFunc_memmove))
-    return false;
-
   // See if the pointers alias.
   if (!AA->isNoAlias(MemoryLocation::getForDest(M),
                      MemoryLocation::getForSource(M)))
@@ -1754,11 +1759,6 @@
   MSSA = MSSA_;
   MemorySSAUpdater MSSAU_(MSSA_);
   MSSAU = MSSA_ ? &MSSAU_ : nullptr;
-  // If we don't have at least memset and memcpy, there is little point of doing
-  // anything here.  These are required by a freestanding implementation, so if
-  // even they are disabled, there is no point in trying hard.
-  if (!TLI->has(LibFunc_memset) || !TLI->has(LibFunc_memcpy))
-    return false;
 
   while (true) {
     if (!iterateOnFunction(F))


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