[PATCH] D105392: [InstCombine] Add optimization to prevent poison from being propagated.

[Hyeongyu Kim via Phabricator via llvm-commits]

hyeongyukim updated this revision to Diff 356393.
hyeongyukim added a comment.

Remove meaningless code, modify the location where freeze inserted and some refactoring.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D105392/new/

https://reviews.llvm.org/D105392

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/freeze.ll


Index: llvm/test/Transforms/InstCombine/freeze.ll
===================================================================
--- llvm/test/Transforms/InstCombine/freeze.ll
+++ llvm/test/Transforms/InstCombine/freeze.ll
@@ -86,3 +86,35 @@
   call void @use_i32_i1(i32 %a, i1 %b)
   ret void
 }
+
+; Move the freeze forward to prevent poison from spreading.
+
+define i32 @early_freeze_test1(i32 %x, i32 %y) {
+; CHECK-LABEL: @early_freeze_test1(
+; CHECK-NEXT:    [[V1:%.*]] = add i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[V1_FR:%.*]] = freeze i32 [[V1]]
+; CHECK-NEXT:    [[V2:%.*]] = shl i32 [[V1_FR]], 1
+; CHECK-NEXT:    [[V3:%.*]] = and i32 [[V2]], 2
+; CHECK-NEXT:    ret i32 [[V3]]
+;
+  %v1 = add i32 %x, %y
+  %v2 = shl i32 %v1, 1
+  %v3 = and i32 %v2, 2
+  %v3.fr = freeze i32 %v3
+  ret i32 %v3.fr
+}
+
+define i1 @early_freeze_test2(i32* %ptr) {
+; CHECK-LABEL: @early_freeze_test2(
+; CHECK-NEXT:    [[V1:%.*]] = load i32, i32* [[PTR:%.*]], align 4
+; CHECK-NEXT:    [[V1_FR:%.*]] = freeze i32 [[V1]]
+; CHECK-NEXT:    [[V2:%.*]] = and i32 [[V1_FR]], 1
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[V2]], 0
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %v1 = load i32, i32* %ptr
+  %v2 = and i32 %v1, 1
+  %cond = icmp eq i32 %v2, 0
+  %cond.fr = freeze i1 %cond
+  ret i1 %cond.fr
+}
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3525,6 +3525,45 @@
       return NV;
   }
 
+  // Try to push freeze through instructions that propagate but don't produce
+  // poison as far as possible.  If operand of freeze follows three conditions
+  // 1) one-use, 2) does not produce poison and 3) has all but one
+  // guaranteed-non-poison operands then push the freeze through to the one
+  // operand that is not guaranteed non poison.  The actual transform is as
+  // follows.
+  //   Op1 = ... ;                      ; Op1 can be posion
+  //   Op0 = Inst(Op1, NonPoisonOps...) ; Op0 has only one use and only have
+  //                                    ; single guaranteed-non-poison operands
+  //   ... = Freeze(Op0)
+  // =>
+  //   Op1 = ...
+  //   Op1.fr = Freeze(Op1)
+  //   ... = Inst(Op1.fr, NonPoisonOps...)
+  if (auto *Inst = dyn_cast<Instruction>(Op0)) {
+    Value *NotGuaranteedNonPoisonOperand;
+    unsigned NumGuaranteedNonPoisonOperand = 0;
+    for (Use &U : Inst->operands()) {
+      if (isGuaranteedNotToBeUndefOrPoison(U.get()))
+        NumGuaranteedNonPoisonOperand++;
+      else
+        NotGuaranteedNonPoisonOperand = U.get();
+    }
+
+    if (Inst->hasOneUse() && !canCreateUndefOrPoison(dyn_cast<Operator>(Op0)) &&
+        NumGuaranteedNonPoisonOperand ==
+            dyn_cast<Operator>(Op0)->getNumOperands() - 1) {
+      if (Instruction *Op1 =
+              dyn_cast<Instruction>(NotGuaranteedNonPoisonOperand)) {
+        auto &U = *Op1->use_begin();
+        auto *FI = new FreezeInst(Op1, Op1->getName() + ".fr");
+
+        replaceUse(U, FI);
+        FI->insertBefore(Inst);
+        return replaceInstUsesWith(I, Op0);
+      }
+    }
+  }
+
   if (match(Op0, m_Undef())) {
     // If I is freeze(undef), see its uses and fold it to the best constant.
     // - or: pick -1


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