llvm-reduce: Fix introducing unreachable code in simplify conditionals

llvm/test/tools/llvm-reduce/reduce-conditionals.ll

@@ -1,10 +1,12 @@
-; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=simplify-conditionals-true --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t
-; RUN: FileCheck --check-prefixes=RESULT-TRUE %s < %t
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=simplify-conditionals-true --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS,CHECK --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck --check-prefixes=RESULT-TRUE,RESULT,CHECK %s < %t
 
-; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=simplify-conditionals-false --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t
-; RUN: FileCheck --check-prefixes=RESULT-FALSE %s < %t
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=simplify-conditionals-false --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS,CHECK --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck --check-prefixes=RESULT-FALSE,RESULT,CHECK %s < %t
 
-; CHECK-INTERESTINGNESS-LABEL: @func(
+; Make sure there is no unreachable code introduced by the reduction
+
+; CHECK-LABEL: @func_simplifies_true(
 ; CHECK-INTERESTINGNESS: store i32 1,
 
 ; RESULT-TRUE: bb0:
@@ -13,15 +15,98 @@
 ; RESULT-TRUE-NEXT: br label %bb2
 ; RESULT-TRUE-NOT: bb1
 
+; RESULT-FALSE: bb0:
+; RESULT-FALSE-NEXT: store i32 0, ptr null, align 4
+; RESULT-FALSE-NEXT: br i1 %cond0, label %bb1, label %bb2
+
+; RESULT-FALSE: bb1:                                              ; preds = %bb0
+; RESULT-FALSE-NEXT: store i32 1, ptr null, align 4
+; RESULT-FALSE-NEXT: br label %bb3
+
+; RESULT-FALSE: bb2:                                              ; preds = %bb0
+; RESULT-FALSE-NEXT: store i32 2, ptr null, align 4
+; RESULT-FALSE-NEXT: br label %bb3
+
+; RESULT-FALSE: bb3:                                              ; preds = %bb1, %bb2
+; RESULT-FALSE-NEXT: ret void
+define void @func_simplifies_true(i1 %cond0, i1 %cond1) {
+bb0:
+  store i32 0, ptr null
+  br i1 %cond0, label %bb1, label %bb2
+
+bb1:
+  store i32 1, ptr null
+  br i1 %cond1, label %bb2, label %bb3
+
+bb2:
+  store i32 2, ptr null
+  br label %bb3
+
+bb3:
+  ret void
+}
+
+; CHECK-LABEL: @func_simplifies_false(
+; CHECK-INTERESTINGNESS: store i32 0,
+
+; RESULT-TRUE: bb0:
+; RESULT-TRUE: store i32 0, ptr null, align 4
+; RESULT-TRUE-NEXT: store i32 1, ptr null, align 4
+; RESULT-TRUE-NEXT: br label %bb2
+; RESULT-TRUE-NOT: bb1
+
 
 ; RESULT-FALSE: bb0:
 ; RESULT-FALSE: store i32 0, ptr null, align 4
 ; RESULT-FALSE-NEXT: br label %bb2
 
-; RESULT-FALSE: bb1: ; No predecessors!
-; RESULT-FALSE-NEXT: store i32 1, ptr null, align 4
+; RESULT-FALSE: bb2: ; preds = %bb0
+; RESULT-FALSE-NEXT: store i32 2, ptr null, align 4
 ; RESULT-FALSE-NEXT: br label %bb3
-define void @func(i1 %cond0, i1 %cond1) {
+
+; RESULT-FALSE: bb3: ; preds = %bb2
+; RESULT-FALSE-NEXT: ret void
+define void @func_simplifies_false(i1 %cond0, i1 %cond1) {
+bb0:
+  store i32 0, ptr null
+  br i1 %cond0, label %bb1, label %bb2
+
+bb1:
+  store i32 1, ptr null
+  br i1 %cond1, label %bb2, label %bb3
+
+bb2:
+  store i32 2, ptr null
+  br label %bb3
+
+bb3:
+  ret void
+}
+
+; Make sure we don't break the reduction in the other functions by
+; having something interesting in unrelated unreachable code.
+
+; CHECK-LABEL: @func_simplifies_true_with_interesting_unreachable_code(
+; CHECK-INTERESTINGNESS: store i32 0,
+; CHECK-INTERESTINGNESS: store i32 %arg,
+
+
+; RESULT: bb0:
+; RESULT-NEXT: store i32 0
+; RESULT-NEXT: br i1 %cond0, label %bb1, label %bb2
+
+; RESULT: bb1:
+; RESULT-NEXT: store i32 1
+; RESULT-NEXT: br i1 %cond1, label %bb2, label %bb3
+
+; RESULT: bb2:
+; RESULT-NEXT: store i32 2
+; RESULT-NEXT: br label %bb3
+
+; RESULT: dead_code: ; preds = %dead_code
+; RESULT-NEXT: store i32 %arg,
+; RESULT-NEXT: br label %dead_code
+define void @func_simplifies_true_with_interesting_unreachable_code(i1 %cond0, i1 %cond1, i32 %arg) {
 bb0:
   store i32 0, ptr null
   br i1 %cond0, label %bb1, label %bb2
@@ -36,4 +121,35 @@ bb2:
 
 bb3:
   ret void
+
+dead_code:
+  store i32 %arg, ptr null
+  br label %dead_code
+}
+
+@block_address_user = constant [1 x ptr] [ptr blockaddress(@will_be_unreachable_blockaddress_use, %will_be_unreachable)]
+
+; CHECK-LABEL: @will_be_unreachable_blockaddress_use(
+; CHECK-INTERESTINGNESS: inttoptr
+
+; RESULT-FALSE: entry:
+; RESULT-FALSE-NEXT: %i2p = inttoptr i64 %int to ptr
+; RESULT-FALSE-NEXT: br label %exit
+
+; RESULT-FALSE: exit: ; preds = %entry
+; RESULT-FALSE-NEXT: ret i1 false
+define i1 @will_be_unreachable_blockaddress_use(i1 %cond, i64 %int) {
+entry:
+  %i2p = inttoptr i64 %int to ptr
+  br i1 %cond, label %will_be_unreachable, label %exit
+
+will_be_unreachable:
+  %load = load ptr, ptr %i2p, align 8
+  br label %for.body
+
+for.body:
+  br label %for.body
+
+exit:
+  ret i1 false
 }

llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp

@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "ReduceUsingSimplifyCFG.h"
+#include "Utils.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Instructions.h"
@@ -35,13 +36,17 @@ void llvm::reduceUsingSimplifyCFGDeltaPass(Oracle &O,
 static void reduceConditionals(Oracle &O, ReducerWorkItem &WorkItem,
                                bool Direction) {
   Module &M = WorkItem.getModule();
-  SmallVector<BasicBlock *, 16> ToSimplify;
 
   LLVMContext &Ctx = M.getContext();
   ConstantInt *ConstValToSet =
       Direction ? ConstantInt::getTrue(Ctx) : ConstantInt::getFalse(Ctx);
 
-  for (auto &F : M) {
+  for (Function &F : M) {
+    if (F.isDeclaration())
+      continue;
+
+    SmallVector<BasicBlock *, 16> ToSimplify;
+
     for (auto &BB : F) {
       auto *BR = dyn_cast<BranchInst>(BB.getTerminator());
       if (!BR || !BR->isConditional() || BR->getCondition() == ConstValToSet ||
@@ -51,11 +56,13 @@ static void reduceConditionals(Oracle &O, ReducerWorkItem &WorkItem,
       BR->setCondition(ConstValToSet);
       ToSimplify.push_back(&BB);
     }
-  }
 
-  TargetTransformInfo TTI(M.getDataLayout());
-  for (auto *BB : ToSimplify)
-    simplifyCFG(BB, TTI);
+    if (!ToSimplify.empty()) {
+      // TODO: Should probably leave MergeBlockIntoPredecessor for a separate
+      // reduction
+      simpleSimplifyCFG(F, ToSimplify);
+    }
+  }
 }
 
 void llvm::reduceConditionalsTrueDeltaPass(Oracle &O,

llvm/tools/llvm-reduce/deltas/Utils.cpp

@@ -14,6 +14,8 @@
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/GlobalAlias.h"
 #include "llvm/IR/GlobalIFunc.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
 
 using namespace llvm;
 
@@ -47,3 +49,40 @@ bool llvm::hasAliasOrBlockAddressUse(Function &F) {
     return isa<GlobalAlias, GlobalIFunc, BlockAddress>(U);
   });
 }
+
+void llvm::simpleSimplifyCFG(Function &F, ArrayRef<BasicBlock *> BBs,
+                             bool FoldBlockIntoPredecessor) {
+
+  for (BasicBlock *BB : BBs) {
+    ConstantFoldTerminator(BB);
+    if (FoldBlockIntoPredecessor)
+      MergeBlockIntoPredecessor(BB);
+  }
+
+  // Remove unreachable blocks
+  //
+  // removeUnreachableBlocks can't be used here, it will turn various undefined
+  // behavior into unreachables, but llvm-reduce was the thing that generated
+  // the undefined behavior, and we don't want it to kill the entire program.
+  SmallPtrSet<BasicBlock *, 16> Visited(llvm::from_range,
+                                        depth_first(&F.getEntryBlock()));
+
+  SmallVector<BasicBlock *, 16> Unreachable;
+  for (BasicBlock &BB : F) {
+    if (!Visited.count(&BB))
+      Unreachable.push_back(&BB);
+  }
+
+  // The dead BB's may be in a dead cycle or otherwise have references to each
+  // other.  Because of this, we have to drop all references first, then delete
+  // them all at once.
+  for (BasicBlock *BB : Unreachable) {
+    for (BasicBlock *Successor : successors(&*BB))
+      if (Visited.count(Successor))
+        Successor->removePredecessor(&*BB);
+    BB->dropAllReferences();
+  }
+
+  for (BasicBlock *BB : Unreachable)
+    BB->eraseFromParent();
+}

llvm/tools/llvm-reduce/deltas/Utils.h

@@ -16,6 +16,7 @@
 #include "llvm/Support/CommandLine.h"
 
 namespace llvm {
+class BasicBlock;
 class Function;
 class Type;
 class Value;
@@ -26,6 +27,11 @@ Value *getDefaultValue(Type *T);
 bool hasAliasUse(Function &F);
 bool hasAliasOrBlockAddressUse(Function &F);
 
+// Constant fold terminators in \p and minimally prune unreachable code from the
+// function.
+void simpleSimplifyCFG(Function &F, ArrayRef<BasicBlock *> BBs,
+                       bool FoldBlockIntoPredecessor = true);
+
 } // namespace llvm
 
 #endif