[PATCH] D143641: [MemorySSA] Recursively check if gep's pointer operand is a guaranteed loop invariant

[luxufan via Phabricator via llvm-commits]

StephenFan created this revision.
StephenFan added reviewers: nikic, asbirlea.
Herald added subscribers: kmitropoulou, hiraditya.
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On the past, we just check if gep's pointer operand is a non-instruction
operand or is a alloca instruction to decide if it is guaranteed to be
a loop invariant. If the gep's pointer operand is also a gep then it would
be considered to be a non-guaranteed loop invariant. This patch makes
MemorySSA Recursively checking if gep's pointer operand is guaranteed
to be a loop invariant.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D143641

Files:
  llvm/lib/Analysis/MemorySSA.cpp
  llvm/test/Analysis/MemorySSA/loop-invariant.ll


Index: llvm/test/Analysis/MemorySSA/loop-invariant.ll
===================================================================
--- llvm/test/Analysis/MemorySSA/loop-invariant.ll
+++ llvm/test/Analysis/MemorySSA/loop-invariant.ll
@@ -4,7 +4,7 @@
 ; %p2 is a loop invariant and the MemoryLoc of load instr and store inst in
 ; loop block are NoAlias
 ;
-; CHECK: MemoryUse(2)
+; CHECK: MemoryUse(liveOnEntry)
 ; CHECK: %val = load i32, ptr %p2
 define void @gep(ptr %ptr) {
 entry:
@@ -24,7 +24,8 @@
   br label %loop
 }
 
-; CHECK: MemoryUse(2)
+; CHECK: %x = phi i32 [ 0, %tmp ], [ %x.inc, %loop ]
+; CHECK-NEXT: MemoryUse(liveOnEntry)
 ; CHECK-NEXT: %val = load i32, ptr %p2
 define void @load_entry_block(ptr %ptr, ptr %addr) {
 entry:
Index: llvm/lib/Analysis/MemorySSA.cpp
===================================================================
--- llvm/lib/Analysis/MemorySSA.cpp
+++ llvm/lib/Analysis/MemorySSA.cpp
@@ -2625,21 +2625,18 @@
 }
 
 bool upward_defs_iterator::IsGuaranteedLoopInvariant(const Value *Ptr) const {
-  auto IsGuaranteedLoopInvariantBase = [](const Value *Ptr) {
-    Ptr = Ptr->stripPointerCasts();
-    if (!isa<Instruction>(Ptr))
-      return true;
-    return isa<AllocaInst>(Ptr);
-  };
-
   Ptr = Ptr->stripPointerCasts();
   if (auto *I = dyn_cast<Instruction>(Ptr)) {
     if (I->getParent()->isEntryBlock())
       return true;
   }
+
   if (auto *GEP = dyn_cast<GEPOperator>(Ptr)) {
-    return IsGuaranteedLoopInvariantBase(GEP->getPointerOperand()) &&
+    return IsGuaranteedLoopInvariant(GEP->getPointerOperand()) &&
            GEP->hasAllConstantIndices();
   }
-  return IsGuaranteedLoopInvariantBase(Ptr);
+
+  if (!isa<Instruction>(Ptr))
+    return true;
+  return isa<AllocaInst>(Ptr);
 }


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