[PATCH] D136524: [InstCombine] Handle select inst when eliminating constant memcpy

[Anshil Gandhi via Phabricator via llvm-commits]

gandhi21299 updated this revision to Diff 490302.
gandhi21299 added a comment.
Herald added a subscriber: StephenFan.

- Rebased against the latest revision.
- Check if the true and false values of SelectInst are already in the Worklist before inserting the SelectInst itself into the Worklist.
- Define a new SelectInst while preserving the attached MetaData.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D136524/new/

https://reviews.llvm.org/D136524

Files:
  llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
  llvm/test/Transforms/InstCombine/ptr-replace-alloca.ll
  llvm/test/Transforms/InstCombine/replace-alloca-phi.ll


Index: llvm/test/Transforms/InstCombine/ptr-replace-alloca.ll
===================================================================
--- llvm/test/Transforms/InstCombine/ptr-replace-alloca.ll
+++ llvm/test/Transforms/InstCombine/ptr-replace-alloca.ll
@@ -337,6 +337,39 @@
   ret i32 %v
 }
 
+define i8 @select_same_addrspace_remove_alloca(i1 %cond, ptr %p) {
+; CHECK-LABEL: @select_same_addrspace_remove_alloca(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[PTR:%.*]] = select i1 %cond, ptr [[G1:@.*]], ptr [[P:%.*]]
+; CHECK-NEXT:    [[LOAD:%.*]] = load i8, ptr [[PTR]], align 1
+; CHECK-NEXT:    ret i8 [[LOAD]]
+;
+entry:
+  %alloca = alloca [32 x i8]
+  call void @llvm.memcpy.p0.p0.i64(ptr %alloca, ptr @g1, i64 256, i1 false)
+  %ptr = select i1 %cond, ptr %alloca, ptr %p
+  %load = load i8, ptr %ptr
+  ret i8 %load
+}
+
+define i8 @select_diff_addrspace_keep_alloca(i1 %cond, ptr addrspace(1) %p) {
+; CHECK-LABEL: @select_diff_addrspace_keep_alloca(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    %alloca = alloca [32 x i8], align 1, addrspace(1)
+; CHECK-NEXT:    call void @llvm.memcpy.p1.p0.i64(ptr addrspace(1) noundef align 1 dereferenceable(256) %alloca, ptr noundef nonnull align 16 dereferenceable(256) @g1, i64 256, i1 false)
+; CHECK-NEXT:    %ptr = select i1 %cond, ptr addrspace(1) %alloca, ptr addrspace(1) %p
+; CHECK-NEXT:    %load = load i8, ptr addrspace(1) %ptr, align 1
+; CHECK-NEXT:    ret i8 %load
+;
+entry:
+  %alloca = alloca [32 x i8], addrspace(1)
+  call void @llvm.memcpy.p1.p0.i64(ptr addrspace(1) %alloca, ptr @g1, i64 256, i1 false)
+  %ptr = select i1 %cond, ptr addrspace(1) %alloca, ptr addrspace(1) %p
+  %load = load i8, ptr addrspace(1) %ptr
+  ret i8 %load
+}
+
 declare void @llvm.memcpy.p1.p0.i64(ptr addrspace(1), ptr, i64, i1)
 declare void @llvm.memcpy.p0.p0.i64(ptr, ptr, i64, i1)
 declare void @llvm.memcpy.p0.p1.i64(ptr, ptr addrspace(1), i64, i1)
+declare void @llvm.memcpy.p5i8.p4i8.i64([32 x i8] addrspace(5)*, [32 x i8] addrspace(4)*, i64, i1)
Index: llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -79,7 +79,7 @@
         Worklist.emplace_back(I, true);
         continue;
       }
-      if (isa<BitCastInst>(I) || isa<AddrSpaceCastInst>(I)) {
+      if (isa<BitCastInst, AddrSpaceCastInst, SelectInst>(I)) {
         // If uses of the bitcast are ok, we are ok.
         Worklist.emplace_back(I, IsOffset);
         continue;
@@ -315,6 +315,19 @@
       Worklist.insert(PHI);
       if (!collectUsersRecursive(*PHI))
         return false;
+    } else if (auto *SI = dyn_cast<SelectInst>(Inst)) {
+      if (!isa<Instruction>(SI->getTrueValue()) ||
+          !isa<Instruction>(SI->getFalseValue()))
+        return false;
+
+      if (!Worklist.contains(cast<Instruction>(SI->getTrueValue())) ||
+          !Worklist.contains(cast<Instruction>(SI->getFalseValue()))) {
+        ValuesToRevisit.insert(Inst);
+        continue;
+      }
+      Worklist.insert(SI);
+      if (!collectUsersRecursive(*SI))
+        return false;
     } else if (isa<GetElementPtrInst, BitCastInst>(Inst)) {
       Worklist.insert(Inst);
       if (!collectUsersRecursive(*Inst))
@@ -380,6 +393,13 @@
     IC.InsertNewInstWith(NewI, *BC);
     NewI->takeName(BC);
     WorkMap[BC] = NewI;
+  } else if (auto *SI = dyn_cast<SelectInst>(I)) {
+    auto *NewSI = SelectInst::Create(
+        SI->getCondition(), getReplacement(SI->getTrueValue()),
+        getReplacement(SI->getFalseValue()), SI->getName(), nullptr, SI);
+    IC.InsertNewInstWith(NewSI, *SI);
+    NewSI->takeName(SI);
+    WorkMap[SI] = NewSI;
   } else if (auto *MemCpy = dyn_cast<MemTransferInst>(I)) {
     auto *SrcV = getReplacement(MemCpy->getRawSource());
     // The pointer may appear in the destination of a copy, but we don't want to


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