[llvm] Fix Issue 65107 (PR #78444)
via llvm-commits
llvm-commits at lists.llvm.org
Wed Jan 17 05:31:59 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: hanbeom (ParkHanbum)
<details>
<summary>Changes</summary>
After we move instruction to an unreachable basic block, we need to
handle it appropriately. if not,
`removeAllNonTerminatorAndEHPadInstructions` is called within
`prepareWorklist` preparing for the second combining process, and
instructions in the unreachable block are processed.
in this case, we are considered to have modified instruction, so
message `LLVM ERROR: Instruction Combining did not reach a fixpoint
after 1 iterations` is showing and exits.
---
Full diff: https://github.com/llvm/llvm-project/pull/78444.diff
3 Files Affected:
- (modified) llvm/lib/Transforms/InstCombine/InstCombineInternal.h (+1-1)
- (modified) llvm/lib/Transforms/InstCombine/InstructionCombining.cpp (+22-3)
- (modified) llvm/test/Transforms/InstCombine/sink_to_unreachable.ll (+72)
``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 21c61bd990184d..5a1e1726946510 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -736,7 +736,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
bool removeInstructionsBeforeUnreachable(Instruction &I);
void addDeadEdge(BasicBlock *From, BasicBlock *To,
SmallVectorImpl<BasicBlock *> &Worklist);
- void handleUnreachableFrom(Instruction *I,
+ bool handleUnreachableFrom(Instruction *I,
SmallVectorImpl<BasicBlock *> &Worklist);
void handlePotentiallyDeadBlocks(SmallVectorImpl<BasicBlock *> &Worklist);
void handlePotentiallyDeadSuccessors(BasicBlock *BB, BasicBlock *LiveSucc);
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 7f2018b3a19958..f4411e52376ff3 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3082,22 +3082,23 @@ void InstCombinerImpl::addDeadEdge(BasicBlock *From, BasicBlock *To,
// Under the assumption that I is unreachable, remove it and following
// instructions. Changes are reported directly to MadeIRChange.
-void InstCombinerImpl::handleUnreachableFrom(
+bool InstCombinerImpl::handleUnreachableFrom(
Instruction *I, SmallVectorImpl<BasicBlock *> &Worklist) {
+ bool Changed = false;
BasicBlock *BB = I->getParent();
for (Instruction &Inst : make_early_inc_range(
make_range(std::next(BB->getTerminator()->getReverseIterator()),
std::next(I->getReverseIterator())))) {
if (!Inst.use_empty() && !Inst.getType()->isTokenTy()) {
replaceInstUsesWith(Inst, PoisonValue::get(Inst.getType()));
- MadeIRChange = true;
+ Changed = true;
}
if (Inst.isEHPad() || Inst.getType()->isTokenTy())
continue;
// RemoveDIs: erase debug-info on this instruction manually.
Inst.dropDbgValues();
eraseInstFromFunction(Inst);
- MadeIRChange = true;
+ Changed = true;
}
// RemoveDIs: to match behaviour in dbg.value mode, drop debug-info on
@@ -3107,6 +3108,8 @@ void InstCombinerImpl::handleUnreachableFrom(
// Handle potentially dead successors.
for (BasicBlock *Succ : successors(BB))
addDeadEdge(BB, Succ, Worklist);
+
+ return MadeIRChange = (Changed | MadeIRChange);
}
void InstCombinerImpl::handlePotentiallyDeadBlocks(
@@ -4396,6 +4399,22 @@ bool InstCombinerImpl::run() {
for (Use &U : I->operands())
if (Instruction *OpI = dyn_cast<Instruction>(U.get()))
Worklist.push(OpI);
+
+ // When we sink instruction, we must consider the case
+ // where the baisc block to which the instruction is moved
+ // is unreachable. Otherwise, a problem occurs where the
+ // sinked instruction removes the instruction from the
+ // second loop.
+ if (all_of(predecessors(UserParent), [&](BasicBlock *Pred) {
+ return DeadEdges.contains({Pred, UserParent}) ||
+ DT.dominates(UserParent, Pred);
+ })) {
+ SmallVector<BasicBlock *> DeadBlockCandidates;
+ if (handleUnreachableFrom(I, DeadBlockCandidates)) {
+ handlePotentiallyDeadBlocks(DeadBlockCandidates);
+ continue;
+ }
+ }
}
}
diff --git a/llvm/test/Transforms/InstCombine/sink_to_unreachable.ll b/llvm/test/Transforms/InstCombine/sink_to_unreachable.ll
index e788b634da8868..193b0d5a704093 100644
--- a/llvm/test/Transforms/InstCombine/sink_to_unreachable.ll
+++ b/llvm/test/Transforms/InstCombine/sink_to_unreachable.ll
@@ -157,3 +157,75 @@ bb3:
%p = phi i32 [0, %bb1], [%a, %bb2]
ret i32 %p
}
+
+define i1 @src_sink_and_remove_bb(i16 %0) {
+; CHECK-LABEL: @src_sink_and_remove_bb(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[BB1:%.*]]
+; CHECK: bb1:
+; CHECK-NEXT: br i1 true, label [[BB1]], label [[UNREACHABLE:%.*]]
+; CHECK: unreachable:
+; CHECK-NEXT: ret i1 poison
+;
+entry:
+ br label %bb1
+bb1:
+ %unknown = icmp ult i16 255, %0
+ br i1 true, label %bb1, label %unreachable
+unreachable:
+ ret i1 %unknown
+}
+
+define i1 @src_sink_and_remove_entry(i16 %0) {
+; CHECK-LABEL: @src_sink_and_remove_entry(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[BB1:%.*]]
+; CHECK: bb1:
+; CHECK-NEXT: br i1 true, label [[BB1]], label [[UNREACHABLE:%.*]]
+; CHECK: unreachable:
+; CHECK-NEXT: ret i1 poison
+;
+entry:
+ %unknown = icmp ult i16 255, %0
+ br label %bb1
+bb1:
+ br i1 true, label %bb1, label %unreachable
+unreachable:
+ ret i1 %unknown
+}
+
+define i1 @src_sink_and_remove(i8 %0) {
+; CHECK-LABEL: @src_sink_and_remove(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[BB1:%.*]]
+; CHECK: bb1:
+; CHECK-NEXT: br i1 false, label [[UNREACHABLE:%.*]], label [[BB1]]
+; CHECK: unreachable:
+; CHECK-NEXT: ret i1 poison
+;
+entry:
+ %unknown = icmp ult i8 255, %0
+ br label %bb1
+bb1:
+ br i1 false, label %unreachable, label %bb1
+unreachable:
+ ret i1 %unknown
+}
+
+define i1 @src_sink_and_combine(i8 %0) {
+; CHECK-LABEL: @src_sink_and_combine(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[BB1:%.*]]
+; CHECK: bb1:
+; CHECK-NEXT: br i1 false, label [[BB1]], label [[UNREACHABLE:%.*]]
+; CHECK: unreachable:
+; CHECK-NEXT: ret i1 false
+;
+entry:
+ br label %bb1
+bb1:
+ %unknown = icmp ult i8 255, %0
+ br i1 false, label %bb1, label %unreachable
+unreachable:
+ ret i1 %unknown
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/78444
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