Revert "NewGVN: Make unreachable blocks be marked with unreachable"

This reverts commit r293196

Besides making things look nicer, ATM, we'd like to preserve analysis
more than we'd like to destroy the CFG.  We'll probably revisit in the future

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293501 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/NewGVN.cpp b/lib/Transforms/Scalar/NewGVN.cpp
index c17b9f7fcf24388350c6d78d15edf9da18826cc6..259a4eade0dbe06def558ee423ab16046ae0fe50 100644 (file)
--- a/lib/Transforms/Scalar/NewGVN.cpp
+++ b/lib/Transforms/Scalar/NewGVN.cpp
@@ -2106,21 +2106,26 @@ void NewGVN::deleteInstructionsInBlock(BasicBlock *BB) {
   DEBUG(dbgs() << "  BasicBlock Dead:" << *BB);
   ++NumGVNBlocksDeleted;
 
-  // Change to unreachable does not handle destroying phi nodes. We just replace
-  // the users with undef.
-  if (BB->empty())
+  // Check to see if there are non-terminating instructions to delete.
+  if (isa<TerminatorInst>(BB->begin()))
     return;
-  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);
+  // 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;
+  }
 }
 
 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 05fe2a22a3f539d859d008b4a4262da6c02f6e80..c1b5cc81fb5174e45e6844118a3b8dd1e9e7569a 100644 (file)
--- a/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll
+++ b/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll
@@ -1,4 +1,3 @@
-; 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"
@@ -10,29 +9,30 @@ 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 11b44ede6d756d0e0bf7ebf0e17fd025a27378e4..c24b03278b7c350051d9377da07dd5c2f11dda86 100644 (file)
--- a/test/Transforms/NewGVN/pr31594.ll
+++ b/test/Transforms/NewGVN/pr31594.ll
@@ -77,7 +77,7 @@ define void @foo(i8* %arg) {
 ; CHECK-NEXT:    i8 6, label [[BB8:%.*]]
 ; CHECK-NEXT:    ]
 ; CHECK:       bb8:
-; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    br label [[BB4]]
 ; CHECK:       bb9:
 ; CHECK-NEXT:    store i8 0, i8* [[ARG]], !g !0
 ; CHECK-NEXT:    unreachable