[llvm] r293501 - Revert "NewGVN: Make unreachable blocks be marked with unreachable"

[Daniel Berlin via llvm-commits]

Author: dannyb
Date: Mon Jan 30 11:06:55 2017
New Revision: 293501

URL: http://llvm.org/viewvc/llvm-project?rev=293501&view=rev
Log:
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

Modified:
    llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp
    llvm/trunk/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll
    llvm/trunk/test/Transforms/NewGVN/pr31594.ll

Modified: llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp?rev=293501&r1=293500&r2=293501&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp Mon Jan 30 11:06:55 2017
@@ -2106,21 +2106,26 @@ void NewGVN::deleteInstructionsInBlock(B
   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) {

Modified: llvm/trunk/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll?rev=293501&r1=293500&r2=293501&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll (original)
+++ llvm/trunk/test/Transforms/NewGVN/2008-12-09-SelfRemove.ll Mon Jan 30 11:06:55 2017
@@ -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: }

Modified: llvm/trunk/test/Transforms/NewGVN/pr31594.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/NewGVN/pr31594.ll?rev=293501&r1=293500&r2=293501&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/NewGVN/pr31594.ll (original)
+++ llvm/trunk/test/Transforms/NewGVN/pr31594.ll Mon Jan 30 11:06:55 2017
@@ -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