[PATCH] D108826: [SLP][LTO][WIP]Allow full SLP in LTO only at link time.

[Alexey Bataev via Phabricator via cfe-commits]

ABataev created this revision.
Herald added subscribers: hiraditya, inglorion.
ABataev requested review of this revision.
Herald added projects: clang, LLVM.
Herald added subscribers: llvm-commits, cfe-commits.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D108826

Files:
  clang/lib/Driver/ToolChains/Clang.cpp
  llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp


Index: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -172,6 +172,10 @@
     cl::desc("The maximum number of users to visit while visiting the "
              "predecessors. This prevents compilation time increase."));
 
+static cl::opt<bool> SLPLimitToRegSize(
+    "slp-limit-to-reg-size", cl::init(false), cl::Hidden,
+    cl::desc("Try to vectorize using only maximal vector register size."));
+
 static cl::opt<bool>
     ViewSLPTree("view-slp-tree", cl::Hidden,
                 cl::desc("Display the SLP trees with Graphviz"));
@@ -7453,7 +7457,8 @@
   const unsigned MinVF = R.getMinVecRegSize() / Sz;
   unsigned VF = Chain.size();
 
-  if (!isPowerOf2_32(Sz) || !isPowerOf2_32(VF) || VF < 2 || VF < MinVF)
+  if (!isPowerOf2_32(Sz) || !isPowerOf2_32(VF) || VF < 2 || VF < MinVF ||
+      (SLPLimitToRegSize && VF < R.getMaxVecRegSize() / Sz))
     return false;
 
   LLVM_DEBUG(dbgs() << "SLP: Analyzing " << VF << " stores at offset " << Idx
@@ -7717,6 +7722,7 @@
   Type *ScalarTy = VL[0]->getType();
   if (auto *IE = dyn_cast<InsertElementInst>(VL[0]))
     ScalarTy = IE->getOperand(1)->getType();
+  unsigned MaxRegSz = R.getMaxVecRegSize() / Sz;
 
   unsigned NextInst = 0, MaxInst = VL.size();
   for (unsigned VF = MaxVF; NextInst + 1 < MaxInst && VF >= MinVF; VF /= 2) {
@@ -7737,7 +7743,8 @@
       if (!isPowerOf2_32(OpsWidth))
         continue;
 
-      if ((VF > MinVF && OpsWidth <= VF / 2) || (VF == MinVF && OpsWidth < 2))
+      if ((SLPLimitToRegSize && OpsWidth < MaxRegSz) ||
+          (VF > MinVF && OpsWidth <= VF / 2) || (VF == MinVF && OpsWidth < 2))
         break;
 
       ArrayRef<Value *> Ops = VL.slice(I, OpsWidth);
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -6441,8 +6441,13 @@
   OptSpecifier SLPVectAliasOption =
       EnableSLPVec ? options::OPT_O_Group : options::OPT_fslp_vectorize;
   if (Args.hasFlag(options::OPT_fslp_vectorize, SLPVectAliasOption,
-                   options::OPT_fno_slp_vectorize, EnableSLPVec))
+                   options::OPT_fno_slp_vectorize, EnableSLPVec)) {
     CmdArgs.push_back("-vectorize-slp");
+    if (IsUsingLTO) {
+      CmdArgs.push_back("-mllvm");
+      CmdArgs.push_back("-slp-limit-to-reg-size");
+    }
+  }
 
   ParseMPreferVectorWidth(D, Args, CmdArgs);
 


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