[CodeGenPrepare] Don't simplify incomplete expression tree in AddrModeCombine

[dtcxzyw]

Since new select/phi instructions may construct loops, the expression tree to be simplified may still be incomplete (i.e., it may contain select with dummy values or phi without incoming values). This patch removes the call to simplifyInstruction for now, as it doesn't break existing tests.

Original PR: https://reviews.llvm.org/D36073
Fix the crash reported in #163453 (comment).

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

Changes

Since new select/phi instructions may construct loops, the expression tree to be simplified may still be incomplete (i.e., it may contain select with dummy values or phi without incoming values). This patch removes the call to simplifyInstruction for now, as it doesn't break existing tests.

Original PR: https://reviews.llvm.org/D36073
Fix the crash reported in #163453 (comment).

---

Full diff: https://github.com/llvm/llvm-project/pull/164628.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/CodeGenPrepare.cpp (+6-36)
• (modified) llvm/test/Transforms/CodeGenPrepare/X86/sink-addrmode-base.ll (+38)

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 9e78ec96a2f27..8ea132626a5af 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -4030,7 +4030,6 @@ bool PhiNodeSetIterator::operator!=(const PhiNodeSetIterator &RHS) const {
 /// if it is simplified.
 class SimplificationTracker {
   DenseMap<Value *, Value *> Storage;
-  const SimplifyQuery &SQ;
   // Tracks newly created Phi nodes. The elements are iterated by insertion
   // order.
   PhiNodeSet AllPhiNodes;
@@ -4038,8 +4037,6 @@ class SimplificationTracker {
   SmallPtrSet<SelectInst *, 32> AllSelectNodes;
 
 public:
-  SimplificationTracker(const SimplifyQuery &sq) : SQ(sq) {}
-
   Value *Get(Value *V) {
     do {
       auto SV = Storage.find(V);
@@ -4049,30 +4046,6 @@ class SimplificationTracker {
     } while (true);
   }
 
-  Value *Simplify(Value *Val) {
-    SmallVector<Value *, 32> WorkList;
-    SmallPtrSet<Value *, 32> Visited;
-    WorkList.push_back(Val);
-    while (!WorkList.empty()) {
-      auto *P = WorkList.pop_back_val();
-      if (!Visited.insert(P).second)
-        continue;
-      if (auto *PI = dyn_cast<Instruction>(P))
-        if (Value *V = simplifyInstruction(cast<Instruction>(PI), SQ)) {
-          for (auto *U : PI->users())
-            WorkList.push_back(cast<Value>(U));
-          Put(PI, V);
-          PI->replaceAllUsesWith(V);
-          if (auto *PHI = dyn_cast<PHINode>(PI))
-            AllPhiNodes.erase(PHI);
-          if (auto *Select = dyn_cast<SelectInst>(PI))
-            AllSelectNodes.erase(Select);
-          PI->eraseFromParent();
-        }
-    }
-    return Get(Val);
-  }
-
   void Put(Value *From, Value *To) { Storage.insert({From, To}); }
 
   void ReplacePhi(PHINode *From, PHINode *To) {
@@ -4133,8 +4106,7 @@ class AddressingModeCombiner {
   /// Common Type for all different fields in addressing modes.
   Type *CommonType = nullptr;
 
-  /// SimplifyQuery for simplifyInstruction utility.
-  const SimplifyQuery &SQ;
+  const DataLayout &DL;
 
   /// Original Address.
   Value *Original;
@@ -4143,8 +4115,8 @@ class AddressingModeCombiner {
   Value *CommonValue = nullptr;
 
 public:
-  AddressingModeCombiner(const SimplifyQuery &_SQ, Value *OriginalValue)
-      : SQ(_SQ), Original(OriginalValue) {}
+  AddressingModeCombiner(const DataLayout &DL, Value *OriginalValue)
+      : DL(DL), Original(OriginalValue) {}
 
   ~AddressingModeCombiner() { eraseCommonValueIfDead(); }
 
@@ -4256,7 +4228,7 @@ class AddressingModeCombiner {
     // Keep track of keys where the value is null. We will need to replace it
     // with constant null when we know the common type.
     SmallVector<Value *, 2> NullValue;
-    Type *IntPtrTy = SQ.DL.getIntPtrType(AddrModes[0].OriginalValue->getType());
+    Type *IntPtrTy = DL.getIntPtrType(AddrModes[0].OriginalValue->getType());
     for (auto &AM : AddrModes) {
       Value *DV = AM.GetFieldAsValue(DifferentField, IntPtrTy);
       if (DV) {
@@ -4306,7 +4278,7 @@ class AddressingModeCombiner {
     // simplification is possible only if original phi/selects were not
     // simplified yet.
     // Using this mapping we can find the current value in AddrToBase.
-    SimplificationTracker ST(SQ);
+    SimplificationTracker ST;
 
     // First step, DFS to create PHI nodes for all intermediate blocks.
     // Also fill traverse order for the second step.
@@ -4465,7 +4437,6 @@ class AddressingModeCombiner {
           PHI->addIncoming(ST.Get(Map[PV]), B);
         }
       }
-      Map[Current] = ST.Simplify(V);
     }
   }
 
@@ -5856,8 +5827,7 @@ bool CodeGenPrepare::optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
   // the graph are compatible.
   bool PhiOrSelectSeen = false;
   SmallVector<Instruction *, 16> AddrModeInsts;
-  const SimplifyQuery SQ(*DL, TLInfo);
-  AddressingModeCombiner AddrModes(SQ, Addr);
+  AddressingModeCombiner AddrModes(*DL, Addr);
   TypePromotionTransaction TPT(RemovedInsts);
   TypePromotionTransaction::ConstRestorationPt LastKnownGood =
       TPT.getRestorationPoint();
diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/sink-addrmode-base.ll b/llvm/test/Transforms/CodeGenPrepare/X86/sink-addrmode-base.ll
index 63fd1845594c6..2570b3b2efc31 100644
--- a/llvm/test/Transforms/CodeGenPrepare/X86/sink-addrmode-base.ll
+++ b/llvm/test/Transforms/CodeGenPrepare/X86/sink-addrmode-base.ll
@@ -951,3 +951,41 @@ fallthrough:
   %v = add i32 %v1, %v2
   ret i32 %v
 }
+
+; Make sure we don't simplify an incomplete expression tree.
+define i8 @pr163453(ptr %p, i1 %cond) {
+; CHECK-LABEL: define i8 @pr163453(
+; CHECK-SAME: ptr [[P:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[P_ADDR_0:%.*]] = getelementptr i8, ptr [[P]], i64 1
+; CHECK-NEXT:    [[TMP0:%.*]] = load i8, ptr [[P]], align 1
+; CHECK-NEXT:    [[INCDEC_PTR11:%.*]] = getelementptr i8, ptr [[P]], i64 2
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND]], ptr [[P_ADDR_0]], ptr [[INCDEC_PTR11]]
+; CHECK-NEXT:    [[LOAD:%.*]] = load i8, ptr [[SPEC_SELECT]], align 1
+; CHECK-NEXT:    ret i8 [[LOAD]]
+;
+entry:
+  br label %for.cond
+
+for.cond:
+  %p.pn = phi ptr [ %p, %entry ], [ %p.addr.0, %for.inc ]
+  %p.addr.0 = getelementptr i8, ptr %p.pn, i64 1
+  br i1 false, label %exit, label %for.body
+
+for.body:
+  %1 = load i8, ptr %p.pn, align 1
+  br i1 false, label %for.inc, label %if.else
+
+if.else:
+  %incdec.ptr11 = getelementptr i8, ptr %p.pn, i64 2
+  %spec.select = select i1 %cond, ptr %p.addr.0, ptr %incdec.ptr11
+  br label %exit
+
+for.inc:
+  br label %for.cond
+
+exit:
+  %p.addr.3 = phi ptr [ %spec.select, %if.else ], [ %p.addr.0, %for.cond ]
+  %load = load i8, ptr %p.addr.3, align 1
+  ret i8 %load
+}

[nikic]

Does SimplificationTracker still do something useful if the Simplify() part is dropped?

Original PR: https://reviews.llvm.org/D36073

There is some talk about tests in the review discussion, but the actual 400 loc commit does not have even a single test :(

[nikic]

Okay, looks like the tests landed in a separate commit for some reason: cde03f3