implement another approach

Author: ro-i

llvm/include/llvm/Transforms/Scalar/JumpThreading.h

@@ -169,6 +169,12 @@ class JumpThreadingPass : public PassInfoMixin<JumpThreadingPass> {
   bool processGuards(BasicBlock *BB);
   bool threadGuard(BasicBlock *BB, IntrinsicInst *Guard, BranchInst *BI);
 
+  // Determine unreachability with a possibly not up-to-date DominatorTree.
+  // If BB is unreachable, return a list of BB and all its predecessors.
+  // Otherwise, return an empty list.
+  SmallVector<BasicBlock *, 32> unreachableFromBB(BasicBlock *BB,
+                                                  DomTreeUpdater *DTU);
+
 private:
   BasicBlock *splitBlockPreds(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
                               const char *Suffix);

llvm/lib/IR/BasicBlock.cpp

@@ -556,14 +556,8 @@ void BasicBlock::removePredecessor(BasicBlock *Pred,
     if (NumPreds == 1)
       continue;
 
-    // Try to replace the PHI node with a constant value, but make sure that
-    // this value isn't using the PHI node. (Except it's a PHI node itself. PHI
-    // nodes are allowed to reference themselves.)
-    if (Value *PhiConstant = Phi.hasConstantValue();
-        PhiConstant &&
-        (!isa<Instruction>(PhiConstant) || isa<PHINode>(PhiConstant) ||
-         llvm::all_of(Phi.users(),
-                      [PhiConstant](User *U) { return U != PhiConstant; }))) {
+    // Try to replace the PHI node with a constant value.
+    if (Value *PhiConstant = Phi.hasConstantValue()) {
       Phi.replaceAllUsesWith(PhiConstant);
       Phi.eraseFromParent();
     }

llvm/lib/Transforms/Scalar/JumpThreading.cpp

@@ -335,15 +335,19 @@ bool JumpThreadingPass::runImpl(Function &F_, FunctionAnalysisManager *FAM_,
       if (&BB == &F->getEntryBlock() || DTU->isBBPendingDeletion(&BB))
         continue;
 
-      if (pred_empty(&BB)) {
+      if (SmallVector<BasicBlock *, 32> Unreachable =
+              unreachableFromBB(&BB, DTU.get());
+          !Unreachable.empty()) {
         // When processBlock makes BB unreachable it doesn't bother to fix up
         // the instructions in it. We must remove BB to prevent invalid IR.
-        LLVM_DEBUG(dbgs() << "  JT: Deleting dead block '" << BB.getName()
-                          << "' with terminator: " << *BB.getTerminator()
-                          << '\n');
-        LoopHeaders.erase(&BB);
-        LVI->eraseBlock(&BB);
-        DeleteDeadBlock(&BB, DTU.get());
+        for (BasicBlock *UBB : Unreachable) {
+          LLVM_DEBUG(dbgs()
+                     << "  JT: Deleting dead block '" << UBB->getName()
+                     << "' with terminator: " << *UBB->getTerminator() << '\n');
+          LoopHeaders.erase(UBB);
+          LVI->eraseBlock(UBB);
+        }
+        DeleteDeadBlocks(Unreachable, DTU.get());
         Changed = ChangedSinceLastAnalysisUpdate = true;
         continue;
       }
@@ -381,6 +385,26 @@ bool JumpThreadingPass::runImpl(Function &F_, FunctionAnalysisManager *FAM_,
   return EverChanged;
 }
 
+SmallVector<BasicBlock *, 32>
+JumpThreadingPass::unreachableFromBB(BasicBlock *BB, DomTreeUpdater *DTU) {
+  if (BB->isEntryBlock() || DTU->isBBPendingDeletion(BB))
+    return {};
+
+  SmallVector<BasicBlock *, 32> Unreachable({BB});
+  SmallPtrSet<BasicBlock *, 32> Seen({BB});
+
+  for (unsigned U = 0; U < Unreachable.size(); ++U) {
+    for (BasicBlock *Pred : predecessors(Unreachable[U])) {
+      if (Pred->isEntryBlock())
+        return {};
+      if (Seen.insert(Pred).second && !DTU->isBBPendingDeletion(Pred))
+        Unreachable.push_back(Pred);
+    }
+  }
+
+  return Unreachable;
+}
+
 // Replace uses of Cond with ToVal when safe to do so. If all uses are
 // replaced, we can remove Cond. We cannot blindly replace all uses of Cond
 // because we may incorrectly replace uses when guards/assumes are uses of

llvm/test/Transforms/JumpThreading/PR33357-lvi-recursion.ll

@@ -1,15 +1,14 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
 ; RUN: opt -S -passes=jump-threading,verify -o - %s | FileCheck %s
 @a = external global i16, align 1
 
-; CHECK-LABEL: f
-; CHECK: bb6:
-; CHECK: bb2:
-; CHECK: bb3:
-; CHECK-NOT: bb0:
-; CHECK-NOT: bb1:
-; CHECK-NOT: bb4:
-; CHECK-NOT: bb5:
 define void @f(i32 %p1) {
+; CHECK-LABEL: define void @f(
+; CHECK-SAME: i32 [[P1:%.*]]) {
+; CHECK-NEXT:  [[BB6:.*:]]
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp eq i32 [[P1]], 0
+; CHECK-NEXT:    ret void
+;
 bb0:
   %0 = icmp eq i32 %p1, 0
   br i1 true, label %bb6, label %bb1

llvm/test/Transforms/JumpThreading/ne-undef.ll

@@ -5,20 +5,7 @@ declare i1 @cond()
 
 define hidden void @hoge(i1 %c1, i32 %x)  {
 ; CHECK-LABEL: @hoge(
-; CHECK-NEXT:  bb:
-; CHECK-NEXT:    br label [[BB13:%.*]]
-; CHECK:       bb4:
-; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne i32 [[TMP7:%.*]], undef
-; CHECK-NEXT:    br i1 [[TMP3]], label [[BB5:%.*]], label [[BB13]]
-; CHECK:       bb5:
-; CHECK-NEXT:    br label [[BB6:%.*]]
-; CHECK:       bb6:
-; CHECK-NEXT:    [[TMP7]] = phi i32 [ [[TMP7]], [[BB5]] ], [ [[X:%.*]], [[BB8:%.*]] ]
-; CHECK-NEXT:    [[C:%.*]] = call i1 @cond()
-; CHECK-NEXT:    br i1 [[C]], label [[BB4:%.*]], label [[BB8]]
-; CHECK:       bb8:
-; CHECK-NEXT:    br label [[BB6]]
-; CHECK:       bb13:
+; CHECK-NEXT:  bb13:
 ; CHECK-NEXT:    ret void
 ;
 bb:

llvm/test/Transforms/JumpThreading/phi-xor-branch.ll

@@ -5,14 +5,7 @@
 
 define void @test() {
 ; CHECK-LABEL: @test(
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br label [[EXIT:%.*]]
-; CHECK:       loop:
-; CHECK-NEXT:    [[DUMMY:%.*]] = phi i16 [ 0, [[LOOP:%.*]] ]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 0, 1
-; CHECK-NEXT:    [[XOR:%.*]] = xor i1 false, [[XOR]]
-; CHECK-NEXT:    br i1 [[XOR]], label [[LOOP]], label [[EXIT]]
-; CHECK:       exit:
+; CHECK-NEXT:  exit:
 ; CHECK-NEXT:    ret void
 ;
 entry:

llvm/test/Transforms/JumpThreading/pr62908.ll

@@ -5,18 +5,7 @@
 
 define i32 @test() {
 ; CHECK-LABEL: define i32 @test() {
-; CHECK-NEXT:  join.thread:
-; CHECK-NEXT:    br label [[END:%.*]]
-; CHECK:       unreachable:
-; CHECK-NEXT:    [[SH_PROM:%.*]] = zext i32 -1 to i64
-; CHECK-NEXT:    [[SHL:%.*]] = shl nsw i64 -1, [[SH_PROM]]
-; CHECK-NEXT:    [[CONV:%.*]] = trunc i64 [[SHL]] to i32
-; CHECK-NEXT:    br label [[JOIN:%.*]]
-; CHECK:       join:
-; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ [[CONV]], [[UNREACHABLE:%.*]] ]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[PHI]], 0
-; CHECK-NEXT:    br i1 [[CMP]], label [[END]], label [[END]]
-; CHECK:       end:
+; CHECK-NEXT:  end:
 ; CHECK-NEXT:    ret i32 0
 ;
 entry:

llvm/test/Transforms/JumpThreading/pr9331.ll

@@ -5,8 +5,6 @@ define void @func(i8 zeroext %p_44) nounwind {
 ; CHECK-LABEL: @func(
 ; CHECK-NEXT:  return:
 ; CHECK-NEXT:    ret void
-; CHECK:       for.inc46:
-; CHECK-NEXT:    br label [[FOR_INC46:%.*]]
 ;
 entry:
   br i1 false, label %for.cond2, label %if.end50

llvm/test/Transforms/JumpThreading/preserving-debugloc-br.ll

@@ -1,15 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
 ; RUN: opt -S -passes=jump-threading < %s | FileCheck %s
 
-; @process_block_branch checks that JumpThreading's processBlock() propagates 
+; @process_block_branch checks that JumpThreading's processBlock() propagates
 ; the debug location to the new branch instruction.
 
 ; @process_threadable_edges_branch checks that JumpThreading's processThreadableEdges()
 ; propagates the debug location to the new branch instruction.
 
 define i32 @process_block_branch(i32 %action) #0 !dbg !5 {
 ; CHECK-LABEL: define i32 @process_block_branch(
-; CHECK:       for.cond:
-; CHECK-NEXT:    br label %for.cond, !dbg [[DBG10:![0-9]+]]
+; CHECK-SAME: i32 [[ACTION:%.*]]) #[[ATTR0:[0-9]+]] !dbg [[DBG5:![0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    switch i32 [[ACTION]], label %[[IF_THEN:.*]] [
+; CHECK-NEXT:      i32 1, label %[[IF_THEN]]
+; CHECK-NEXT:      i32 0, label %[[IF_THEN]]
+; CHECK-NEXT:    ], !dbg [[DBG8:![0-9]+]]
+; CHECK:       [[IF_THEN]]:
+; CHECK-NEXT:    ret i32 undef, !dbg [[DBG9:![0-9]+]]
 ;
 entry:
   switch i32 %action, label %lor.rhs [
@@ -35,8 +42,18 @@ for.body:                                         ; preds = %for.cond
 
 define void @process_threadable_edges_branch(i32 %value) #0 !dbg !15 {
 ; CHECK-LABEL: define void @process_threadable_edges_branch(
-; CHECK:    L0:
-; CHECK:      br label %L2, !dbg [[DBG17:![0-9]+]]
+; CHECK-SAME: i32 [[VALUE:%.*]]) #[[ATTR0]] !dbg [[DBG10:![0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[VALUE]], 32, !dbg [[DBG11:![0-9]+]]
+; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[VALUE]], 64, !dbg [[DBG12:![0-9]+]]
+; CHECK-NEXT:    br i1 [[CMP]], label %[[L0:.*]], label %[[L2:.*]], !dbg [[DBG13:![0-9]+]]
+; CHECK:       [[L0]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @f2(), !dbg [[DBG14:![0-9]+]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @f2(), !dbg [[DBG15:![0-9]+]]
+; CHECK-NEXT:    br label %[[L2]], !dbg [[DBG16:![0-9]+]]
+; CHECK:       [[L2]]:
+; CHECK-NEXT:    call void @f4(i32 [[ADD]]), !dbg [[DBG17:![0-9]+]]
+; CHECK-NEXT:    ret void, !dbg [[DBG18:![0-9]+]]
 ;
 entry:
   %cmp = icmp eq i32 %value, 32, !dbg !16
@@ -78,10 +95,6 @@ attributes #0 = { nounwind }
 !llvm.debugify = !{!2, !3}
 !llvm.module.flags = !{!4}
 
-;.
-; CHECK: [[DBG10]] = !DILocation(line: 6,
-; CHECK: [[DBG17]] = !DILocation(line: 13,
-;.
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
 !1 = !DIFile(filename: "temp.ll", directory: "/")
@@ -111,3 +124,21 @@ attributes #0 = { nounwind }
 !25 = !DILocation(line: 17, column: 1, scope: !15)
 !26 = !DILocation(line: 18, column: 1, scope: !15)
 !27 = !DILocation(line: 19, column: 1, scope: !15)
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C, file: [[META1:![0-9]+]], producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+; CHECK: [[META1]] = !DIFile(filename: "temp.ll", directory: {{.*}})
+; CHECK: [[DBG5]] = distinct !DISubprogram(name: "process_block_branch", linkageName: "process_block_branch", scope: null, file: [[META1]], line: 1, type: [[META6:![0-9]+]], scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]])
+; CHECK: [[META6]] = !DISubroutineType(types: [[META7:![0-9]+]])
+; CHECK: [[META7]] = !{}
+; CHECK: [[DBG8]] = !DILocation(line: 1, column: 1, scope: [[DBG5]])
+; CHECK: [[DBG9]] = !DILocation(line: 2, column: 1, scope: [[DBG5]])
+; CHECK: [[DBG10]] = distinct !DISubprogram(name: "process_threadable_edges_branch", linkageName: "process_threadable_edges_branch", scope: null, file: [[META1]], line: 8, type: [[META6]], scopeLine: 8, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]])
+; CHECK: [[DBG11]] = !DILocation(line: 8, column: 1, scope: [[DBG10]])
+; CHECK: [[DBG12]] = !DILocation(line: 9, column: 1, scope: [[DBG10]])
+; CHECK: [[DBG13]] = !DILocation(line: 10, column: 1, scope: [[DBG10]])
+; CHECK: [[DBG14]] = !DILocation(line: 11, column: 1, scope: [[DBG10]])
+; CHECK: [[DBG15]] = !DILocation(line: 12, column: 1, scope: [[DBG10]])
+; CHECK: [[DBG16]] = !DILocation(line: 13, column: 1, scope: [[DBG10]])
+; CHECK: [[DBG17]] = !DILocation(line: 16, column: 1, scope: [[DBG10]])
+; CHECK: [[DBG18]] = !DILocation(line: 17, column: 1, scope: [[DBG10]])
+;.

llvm/test/Transforms/JumpThreading/removed-use.ll

@@ -1,10 +1,10 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
 ; RUN: opt -S < %s -passes=jump-threading | FileCheck %s
-; CHECK-LABEL: @foo
-; CHECK: bb6:
-; CHECK-NEXT: ret void
-; CHECK: bb3:
-; CHECK: br label %bb3
 define void @foo() {
+; CHECK-LABEL: define void @foo() {
+; CHECK-NEXT:  [[BB6:.*:]]
+; CHECK-NEXT:    ret void
+;
 entry:
   br i1 true, label %bb6, label %bb3
 
@@ -27,9 +27,13 @@ bb6:
   ret void
 }
 
-; CHECK-LABEL: @bar
 ; Just check that we don't crash on this test.
 define void @bar(i1 %p) {
+; CHECK-LABEL: define void @bar(
+; CHECK-SAME: i1 [[P:%.*]]) {
+; CHECK-NEXT:  [[EXIT:.*:]]
+; CHECK-NEXT:    ret void
+;
 entry:
   br i1 false, label %bb2, label %exit
 
@@ -46,7 +50,7 @@ bb4:
 bb5:
   %x1 = phi i32 [ %x0, %bb3 ], [ 0, %bb4 ]
   switch i32 %x1, label %exit [
-    i32 10, label %bb2
+  i32 10, label %bb2
   ]
 
 exit:

llvm/test/Transforms/JumpThreading/unreachable-loops.ll

@@ -12,12 +12,6 @@ define void @unreachable_single_bb_loop() {
 ; CHECK-NEXT:    [[TMP:%.*]] = call i32 @a()
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[TMP]], 1
 ; CHECK-NEXT:    br i1 [[TMP1]], label [[BB8:%.*]], label [[BB8]]
-; CHECK:       bb2:
-; CHECK-NEXT:    [[TMP4:%.*]] = icmp ne i32 [[TMP]], 1
-; CHECK-NEXT:    switch i1 [[TMP4]], label [[BB2:%.*]] [
-; CHECK-NEXT:      i1 false, label [[BB8]]
-; CHECK-NEXT:      i1 true, label [[BB8]]
-; CHECK-NEXT:    ]
 ; CHECK:       bb8:
 ; CHECK-NEXT:    ret void
 ;
@@ -52,14 +46,6 @@ define void @unreachable_multi_bbs_loop() {
 ; CHECK-NEXT:    [[TMP:%.*]] = call i32 @a()
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[TMP]], 1
 ; CHECK-NEXT:    br i1 [[TMP1]], label [[BB8:%.*]], label [[BB8]]
-; CHECK:       bb3:
-; CHECK-NEXT:    br label [[BB2:%.*]]
-; CHECK:       bb2:
-; CHECK-NEXT:    [[TMP4:%.*]] = icmp ne i32 [[TMP]], 1
-; CHECK-NEXT:    switch i1 [[TMP4]], label [[BB3:%.*]] [
-; CHECK-NEXT:      i1 false, label [[BB8]]
-; CHECK-NEXT:      i1 true, label [[BB8]]
-; CHECK-NEXT:    ]
 ; CHECK:       bb8:
 ; CHECK-NEXT:    ret void
 ;
@@ -99,10 +85,6 @@ define void @PR48362(i1 %arg) {
 ; CHECK-LABEL: @PR48362(
 ; CHECK-NEXT:  cleanup.cont1500:
 ; CHECK-NEXT:    unreachable
-; CHECK:       if.end1733:
-; CHECK-NEXT:    [[I82:%.*]] = load i32, ptr undef, align 1
-; CHECK-NEXT:    [[TOBOOL1731_NOT:%.*]] = icmp eq i32 [[I82]], 0
-; CHECK-NEXT:    br label [[IF_END1733:%.*]]
 ;
 cleanup1491:                                      ; preds = %for.body1140
   switch i32 0, label %cleanup2343.loopexit4 [
@@ -189,23 +171,9 @@ cleanup2343.loopexit4:                            ; preds = %cleanup1491
 
 define i32 @constant_phi_leads_to_self_reference(ptr %ptr) {
 ; CHECK-LABEL: @constant_phi_leads_to_self_reference(
-; CHECK-NEXT:    [[A10:%.*]] = alloca i1, align 1
-; CHECK-NEXT:    br label [[F6:%.*]]
-; CHECK:       T3:
-; CHECK-NEXT:    [[L6:%.*]] = phi i1 [ [[C4:%.*]], [[BB6:%.*]] ]
-; CHECK-NEXT:    br label [[BB5:%.*]]
-; CHECK:       BB5:
-; CHECK-NEXT:    [[L10:%.*]] = load i1, ptr [[A10]], align 1
-; CHECK-NEXT:    br i1 [[L10]], label [[BB6]], label [[F6]]
-; CHECK:       BB6:
-; CHECK-NEXT:    [[LGV3:%.*]] = load i1, ptr [[A7:%.*]], align 1
-; CHECK-NEXT:    [[C4]] = icmp sle i1 [[L6]], true
-; CHECK-NEXT:    store i1 [[C4]], ptr [[A7]], align 1
-; CHECK-NEXT:    br i1 [[L6]], label [[F6]], label [[T3:%.*]]
-; CHECK:       F6:
+; CHECK-NEXT:  F6:
+; CHECK-NEXT:    [[A9:%.*]] = alloca i1, align 1
 ; CHECK-NEXT:    ret i32 0
-; CHECK:       F7:
-; CHECK-NEXT:    br label [[BB5]]
 ;
   %A9 = alloca i1, align 1
   br i1 false, label %BB4, label %F6