From 40ef630a4626365faeef8696f611e18d1a69f63a Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Wed, 2 Sep 2009 06:31:02 +0000
Subject: [PATCH] fix PR4815: some cases where DeleteDeadInstruction can delete
 the instruction BBI points to.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80768 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../Scalar/DeadStoreElimination.cpp           | 16 +++++++++---
 test/Transforms/DeadStoreElimination/crash.ll | 26 +++++++++++++++++++
 2 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 test/Transforms/DeadStoreElimination/crash.ll

diff --git a/lib/Transforms/Scalar/DeadStoreElimination.cpp b/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 376a098689d..a7b3e7524fa 100644
--- a/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -83,7 +83,7 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
 
   bool MadeChange = false;
   
-  // Do a top-down walk on the BB
+  // Do a top-down walk on the BB.
   for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ) {
     Instruction *Inst = BBI++;
     
@@ -124,7 +124,10 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
         DeleteDeadInstruction(DepStore);
         NumFastStores++;
         MadeChange = true;
-        
+
+        // DeleteDeadInstruction can delete the current instruction in loop
+        // cases, reset BBI.
+        BBI = Inst;
         if (BBI != BB.begin())
           --BBI;
         continue;
@@ -135,8 +138,15 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
     if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
       if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
           SI->getOperand(0) == DepLoad) {
+        // DeleteDeadInstruction can delete the current instruction.  Save BBI
+        // in case we need it.
+        WeakVH NextInst(BBI);
+        
         DeleteDeadInstruction(SI);
-        if (BBI != BB.begin())
+        
+        if (NextInst == 0)  // Next instruction deleted.
+          BBI = BB.begin();
+        else if (BBI != BB.begin())  // Revisit this instruction if possible.
           --BBI;
         NumFastStores++;
         MadeChange = true;
diff --git a/test/Transforms/DeadStoreElimination/crash.ll b/test/Transforms/DeadStoreElimination/crash.ll
new file mode 100644
index 00000000000..b35bd1aa5ca
--- /dev/null
+++ b/test/Transforms/DeadStoreElimination/crash.ll
@@ -0,0 +1,26 @@
+; RUN: llvm-as < %s | opt -dse | llvm-dis
+
+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"
+target triple = "i386-apple-darwin10.0"
+
+@g80 = external global i8                         ; <i8*> [#uses=3]
+
+declare signext i8 @foo(i8 signext, i8 signext) nounwind readnone ssp
+
+declare i32 @func68(i32) nounwind readonly ssp
+
+; PR4815
+define void @test1(i32 %int32p54) noreturn nounwind ssp {
+entry:
+  br label %bb
+
+bb:                                               ; preds = %bb, %entry
+  %storemerge = phi i8 [ %2, %bb ], [ 1, %entry ] ; <i8> [#uses=1]
+  store i8 %storemerge, i8* @g80
+  %0 = tail call i32 @func68(i32 1) nounwind ssp  ; <i32> [#uses=1]
+  %1 = trunc i32 %0 to i8                         ; <i8> [#uses=1]
+  store i8 %1, i8* @g80, align 1
+  store i8 undef, i8* @g80, align 1
+  %2 = tail call signext i8 @foo(i8 signext undef, i8 signext 1) nounwind ; <i8> [#uses=1]
+  br label %bb
+}
-- 
2.34.1