[PATCH] D105392: [InstCombine] Add optimization to prevent poison from being propagated.
Hyeongyu Kim via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Sun Jul 4 12:39:15 PDT 2021
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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