From 87166905c8d58e152b06752f5d2f24a09ebbcbde Mon Sep 17 00:00:00 2001
From: Ahmed Bougacha <ahmed.bougacha@gmail.com>
Date: Thu, 27 Aug 2015 21:46:04 +0000
Subject: [PATCH] [CodeGen] Check FoldConstantArithmetic result before using
 it.

Fixes PR24602: r245689 introduced an unguarded use of
SelectionDAG::FoldConstantArithmetic, which returns 0 when it fails
because of opaque (hoisted) constants.

llvm-svn: 246217
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp |  5 +++--
 llvm/test/CodeGen/X86/pr24602.ll              | 17 +++++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)
 create mode 100644 llvm/test/CodeGen/X86/pr24602.ll

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 3275daf3ffdd..693331fc19e4 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4457,8 +4457,9 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
   // fold (shl (mul x, c1), c2) -> (mul x, c1 << c2)
   if (N1C && N0.getOpcode() == ISD::MUL && N0.getNode()->hasOneUse()) {
     if (ConstantSDNode *N0C1 = isConstOrConstSplat(N0.getOperand(1))) {
-      SDValue Folded = DAG.FoldConstantArithmetic(ISD::SHL, SDLoc(N1), VT, N0C1, N1C);
-      return DAG.getNode(ISD::MUL, SDLoc(N), VT, N0.getOperand(0), Folded);
+      if (SDValue Folded =
+              DAG.FoldConstantArithmetic(ISD::SHL, SDLoc(N1), VT, N0C1, N1C))
+        return DAG.getNode(ISD::MUL, SDLoc(N), VT, N0.getOperand(0), Folded);
     }
   }
 
diff --git a/llvm/test/CodeGen/X86/pr24602.ll b/llvm/test/CodeGen/X86/pr24602.ll
new file mode 100644
index 000000000000..9c029aeefec9
--- /dev/null
+++ b/llvm/test/CodeGen/X86/pr24602.ll
@@ -0,0 +1,17 @@
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown  | FileCheck %s
+
+; PR24602: Make sure we don't barf on non-foldable code (with opaque constants).
+
+; CHECK-LABEL: pr24602:
+; CHECK-NEXT: # BB#0
+; CHECK-NEXT: movabsq $-10000000000, [[CST:%[a-z0-9]+]]
+; CHECK-NEXT: imulq [[CST]], %rsi
+; CHECK-NEXT: leaq (%rdi,%rsi,8), %rax
+; CHECK-NEXT: movq [[CST]], (%rdi,%rsi,8)
+; CHECK-NEXT: retq
+define i64* @pr24602(i64* %p, i64 %n) nounwind {
+  %mul = mul nsw i64 %n, -10000000000
+  %add.ptr = getelementptr inbounds i64, i64* %p, i64 %mul
+  store i64 -10000000000, i64* %add.ptr
+  ret i64* %add.ptr
+}