From 3eedb093ba260310dc032120096b29dfb983e134 Mon Sep 17 00:00:00 2001
From: Daniel Berlin <dberlin@dberlin.org>
Date: Thu, 26 Jan 2017 18:30:29 +0000
Subject: [PATCH] NewGVN: Make unreachable blocks be marked with unreachable

llvm-svn: 293196
---
 lib/Transforms/Scalar/NewGVN.cpp              | 31 +++++++--------
 .../NewGVN/2008-12-09-SelfRemove.ll           | 38 +++++++++----------
 test/Transforms/NewGVN/pr31594.ll             |  2 +-
 3 files changed, 33 insertions(+), 38 deletions(-)

diff --git a/lib/Transforms/Scalar/NewGVN.cpp b/lib/Transforms/Scalar/NewGVN.cpp
index 747c913278f..bf73375908f 100644
--- a/lib/Transforms/Scalar/NewGVN.cpp
+++ b/lib/Transforms/Scalar/NewGVN.cpp
@@ -1989,26 +1989,21 @@ void NewGVN::deleteInstructionsInBlock(BasicBlock *BB) {
   DEBUG(dbgs() << "  BasicBlock Dead:" << *BB);
   ++NumGVNBlocksDeleted;
 
-  // Check to see if there are non-terminating instructions to delete.
-  if (isa<TerminatorInst>(BB->begin()))
+  // Change to unreachable does not handle destroying phi nodes. We just replace
+  // the users with undef.
+  if (BB->empty())
     return;
-
-  // Delete the instructions backwards, as it has a reduced likelihood of having
-  // to update as many def-use and use-def chains. Start after the terminator.
-  auto StartPoint = BB->rbegin();
-  ++StartPoint;
-  // Note that we explicitly recalculate BB->rend() on each iteration,
-  // as it may change when we remove the first instruction.
-  for (BasicBlock::reverse_iterator I(StartPoint); I != BB->rend();) {
-    Instruction &Inst = *I++;
-    if (!Inst.use_empty())
-      Inst.replaceAllUsesWith(UndefValue::get(Inst.getType()));
-    if (isa<LandingPadInst>(Inst))
-      continue;
-
-    Inst.eraseFromParent();
-    ++NumGVNInstrDeleted;
+  auto BBI = BB->begin();
+  while (auto *Phi = dyn_cast<PHINode>(BBI)) {
+    Phi->replaceAllUsesWith(UndefValue::get(Phi->getType()));
+    ++BBI;
   }
+
+  Instruction *ToKill = &*BBI;
+  // Nothing but phi nodes, so nothing left to remove.
+  if (!ToKill)
+    return;
+  NumGVNInstrDeleted += changeToUnreachable(ToKill, false);
 }
 
 void NewGVN::markInstructionForDeletion(Instruction *I) {
diff --git a/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll b/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll
index c1b5cc81fb5..05fe2a22a3f 100644
--- a/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll
+++ b/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll
@@ -1,3 +1,4 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -newgvn -S | FileCheck %s
 
 target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
@@ -9,30 +10,29 @@ target triple = "i386-apple-darwin9.5"
 	%struct.demangle_component = type { i32, { %struct.anon } }
 
 define void @d_print_mod_list(%struct.d_print_info* %dpi, %struct.d_print_mod* %mods, i32 %suffix) nounwind {
+; CHECK-LABEL: @d_print_mod_list(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr [[STRUCT_D_PRINT_INFO:%.*]], %struct.d_print_info* [[DPI:%.*]], i32 0, i32 1
+; CHECK-NEXT:    br i1 false, label [[RETURN:%.*]], label [[BB:%.*]]
+; CHECK:       bb:
+; CHECK-NEXT:    br label [[BB21:%.*]]
+; CHECK:       bb21:
+; CHECK-NEXT:    br label [[BB21]]
+; CHECK:       return:
+; CHECK-NEXT:    unreachable
+;
 entry:
-	%0 = getelementptr %struct.d_print_info, %struct.d_print_info* %dpi, i32 0, i32 1		; <i8**> [#uses=1]
-	br i1 false, label %return, label %bb
+  %0 = getelementptr %struct.d_print_info, %struct.d_print_info* %dpi, i32 0, i32 1		; <i8**> [#uses=1]
+  br i1 false, label %return, label %bb
 
 bb:		; preds = %entry
-	%1 = load i8*, i8** %0, align 4		; <i8*> [#uses=0]
-	%2 = getelementptr %struct.d_print_info, %struct.d_print_info* %dpi, i32 0, i32 1		; <i8**> [#uses=0]
-	br label %bb21
+  %1 = load i8*, i8** %0, align 4		; <i8*> [#uses=0]
+  %2 = getelementptr %struct.d_print_info, %struct.d_print_info* %dpi, i32 0, i32 1		; <i8**> [#uses=0]
+  br label %bb21
 
 bb21:		; preds = %bb21, %bb
-	br label %bb21
+  br label %bb21
 
 return:		; preds = %entry
-	ret void
+  ret void
 }
-
-; CHECK: define void @d_print_mod_list(%struct.d_print_info* %dpi, %struct.d_print_mod* %mods, i32 %suffix) #0 {
-; CHECK: entry:
-; CHECK:   %0 = getelementptr %struct.d_print_info, %struct.d_print_info* %dpi, i32 0, i32 1
-; CHECK:   br i1 false, label %return, label %bb
-; CHECK: bb:
-; CHECK:   br label %bb21
-; CHECK: bb21:
-; CHECK:   br label %bb21
-; CHECK: return:
-; CHECK:   ret void
-; CHECK: }
diff --git a/test/Transforms/NewGVN/pr31594.ll b/test/Transforms/NewGVN/pr31594.ll
index bca4127d3ae..071fe9b0134 100644
--- a/test/Transforms/NewGVN/pr31594.ll
+++ b/test/Transforms/NewGVN/pr31594.ll
@@ -76,7 +76,7 @@ define void @foo(i8* %arg) {
 ; CHECK-NEXT:    i8 6, label [[BB8:%.*]]
 ; CHECK-NEXT:    ]
 ; CHECK:       bb8:
-; CHECK-NEXT:    br label [[BB4]]
+; CHECK-NEXT:    unreachable
 ; CHECK:       bb9:
 ; CHECK-NEXT:    store i8 0, i8* [[ARG]], !g !0
 ; CHECK-NEXT:    unreachable