From 8f3817f505029e97d28c54548069d5bbaa9d5527 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Mon, 23 Nov 2009 16:13:39 +0000
Subject: [PATCH] Fix a use of an invalidated iterator in the case where there
 are multiple adjacent uses of a dead basic block from the same user. This
 fixes PR5596.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89658 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/SCCP.cpp                |  6 +++-
 .../IPConstantProp/user-with-multiple-uses.ll | 30 +++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/IPConstantProp/user-with-multiple-uses.ll

diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index 977827841d9..d8c59b1d742 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -1871,8 +1871,12 @@ bool IPSCCP::runOnModule(Module &M) {
       BasicBlock *DeadBB = BlocksToErase[i];
       for (Value::use_iterator UI = DeadBB->use_begin(), UE = DeadBB->use_end();
            UI != UE; ) {
+        // Grab the user and then increment the iterator early, as the user
+        // will be deleted. Step past all adjacent uses from the same user.
+        Instruction *I = dyn_cast<Instruction>(*UI);
+        do { ++UI; } while (UI != UE && *UI == I);
+
         // Ignore blockaddress users; BasicBlock's dtor will handle them.
-        Instruction *I = dyn_cast<Instruction>(*UI++);
         if (!I) continue;
 
         bool Folded = ConstantFoldTerminator(I->getParent());
diff --git a/test/Transforms/IPConstantProp/user-with-multiple-uses.ll b/test/Transforms/IPConstantProp/user-with-multiple-uses.ll
new file mode 100644
index 00000000000..402ea41167c
--- /dev/null
+++ b/test/Transforms/IPConstantProp/user-with-multiple-uses.ll
@@ -0,0 +1,30 @@
+; RUN: opt < %s -S -ipsccp | FileCheck %s
+; PR5596
+
+; IPSCCP should propagate the 0 argument, eliminate the switch, and propagate
+; the result.
+
+; CHECK: define i32 @main() noreturn nounwind {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: %call2 = tail call i32 @wwrite(i64 0) nounwind
+; CHECK-NEXT: ret i32 123
+
+define i32 @main() noreturn nounwind {
+entry:
+  %call2 = tail call i32 @wwrite(i64 0) nounwind
+  ret i32 %call2
+}
+
+define internal i32 @wwrite(i64 %i) nounwind readnone {
+entry:
+  switch i64 %i, label %sw.default [
+    i64 3, label %return
+    i64 10, label %return
+  ]
+
+sw.default:
+  ret i32 123
+
+return:
+  ret i32 0
+}
-- 
2.34.1