From 382c1caece181d3f72e7e169702a36b350566751 Mon Sep 17 00:00:00 2001
From: James Molloy <james.molloy@arm.com>
Date: Mon, 16 Feb 2015 17:01:52 +0000
Subject: [PATCH] [LoopReroll] Don't crash on dead code

If a PHI has no users, don't crash; bail gracefully. This shouldn't
happen often, but we can make no guarantees that previous passes didn't leave
dead code around.

llvm-svn: 229405
---
 lib/Transforms/Scalar/LoopRerollPass.cpp |  2 ++
 test/Transforms/LoopReroll/reduction.ll  | 36 ++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/lib/Transforms/Scalar/LoopRerollPass.cpp b/lib/Transforms/Scalar/LoopRerollPass.cpp
index 852f3ed9d51..704299f3041 100644
--- a/lib/Transforms/Scalar/LoopRerollPass.cpp
+++ b/lib/Transforms/Scalar/LoopRerollPass.cpp
@@ -511,6 +511,8 @@ void LoopReroll::SimpleLoopReduction::add(Loop *L) {
   // (including the PHI), except for the last value (which is used by the PHI
   // and also outside the loop).
   Instruction *C = Instructions.front();
+  if (C->user_empty())
+    return;
 
   do {
     C = cast<Instruction>(*C->user_begin());
diff --git a/test/Transforms/LoopReroll/reduction.ll b/test/Transforms/LoopReroll/reduction.ll
index c9991c723ec..a4f168ad1a2 100644
--- a/test/Transforms/LoopReroll/reduction.ll
+++ b/test/Transforms/LoopReroll/reduction.ll
@@ -92,5 +92,41 @@ for.end:                                          ; preds = %for.body
   ret float %add12
 }
 
+define i32 @foo_unusedphi(i32* nocapture readonly %x) #0 {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %r.029 = phi i32 [ 0, %entry ], [ %add12, %for.body ]
+  %arrayidx = getelementptr inbounds i32* %x, i64 %indvars.iv
+  %0 = load i32* %arrayidx, align 4
+  %add = add nsw i32 %0, %0
+  %1 = or i64 %indvars.iv, 1
+  %arrayidx3 = getelementptr inbounds i32* %x, i64 %1
+  %2 = load i32* %arrayidx3, align 4
+  %add4 = add nsw i32 %add, %2
+  %3 = or i64 %indvars.iv, 2
+  %arrayidx7 = getelementptr inbounds i32* %x, i64 %3
+  %4 = load i32* %arrayidx7, align 4
+  %add8 = add nsw i32 %add4, %4
+  %5 = or i64 %indvars.iv, 3
+  %arrayidx11 = getelementptr inbounds i32* %x, i64 %5
+  %6 = load i32* %arrayidx11, align 4
+  %add12 = add nsw i32 %add8, %6
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 4
+  %7 = trunc i64 %indvars.iv.next to i32
+  %cmp = icmp slt i32 %7, 400
+  br i1 %cmp, label %for.body, label %for.end
+
+; CHECK-LABEL: @foo_unusedphi
+; The above is just testing for a crash - no specific output expected.
+
+; CHECK: ret
+
+for.end:                                          ; preds = %for.body
+  ret i32 %add12
+}
+
 attributes #0 = { nounwind readonly uwtable }