From 1a0bbc8a5c1e9cb9888ee8c2ba5f46752636e47f Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Sat, 16 Aug 2014 09:23:42 +0000
Subject: [PATCH] InstCombine: Fix a potential bug in 0 - (X sdiv C)  -> (X
 sdiv -C)

While *most* (X sdiv 1) operations will get caught by InstSimplify, it
is still possible for a sdiv to appear in the worklist which hasn't been
simplified yet.

This means that it is possible for 0 - (X sdiv 1) to get transformed
into (X sdiv -1); dividing by -1 can make the transform produce undef
values instead of the proper result.

Sorry for the lack of testcase, it's a bit problematic because it relies
on the exact order of operations in the worklist.

llvm-svn: 215818
---
 llvm/include/llvm/IR/Constant.h               |  3 +++
 llvm/lib/IR/Constants.cpp                     | 22 +++++++++++++++++++
 .../InstCombine/InstCombineAddSub.cpp         |  2 +-
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/IR/Constant.h b/llvm/include/llvm/IR/Constant.h
index 82ad9fc2f407..d9d163b23ecd 100644
--- a/llvm/include/llvm/IR/Constant.h
+++ b/llvm/include/llvm/IR/Constant.h
@@ -53,6 +53,9 @@ public:
   /// getNullValue.
   bool isNullValue() const;
 
+  /// \brief Returns true if the value is one.
+  bool isOneValue() const;
+
   /// isAllOnesValue - Return true if this is the value that would be returned by
   /// getAllOnesValue.
   bool isAllOnesValue() const;
diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index b815936ac428..23845d8e3b8b 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -107,6 +107,28 @@ bool Constant::isAllOnesValue() const {
   return false;
 }
 
+bool Constant::isOneValue() const {
+  // Check for 1 integers
+  if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))
+    return CI->isOne();
+
+  // Check for FP which are bitcasted from 1 integers
+  if (const ConstantFP *CFP = dyn_cast<ConstantFP>(this))
+    return CFP->getValueAPF().bitcastToAPInt() == 1;
+
+  // Check for constant vectors which are splats of 1 values.
+  if (const ConstantVector *CV = dyn_cast<ConstantVector>(this))
+    if (Constant *Splat = CV->getSplatValue())
+      return Splat->isOneValue();
+
+  // Check for constant vectors which are splats of 1 values.
+  if (const ConstantDataVector *CV = dyn_cast<ConstantDataVector>(this))
+    if (Constant *Splat = CV->getSplatValue())
+      return Splat->isOneValue();
+
+  return false;
+}
+
 bool Constant::isMinSignedValue() const {
   // Check for INT_MIN integers
   if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index b18c10dd57b6..22cc34d861a5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1583,7 +1583,7 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
 
     // 0 - (X sdiv C)  -> (X sdiv -C)  provided the negation doesn't overflow.
     if (match(Op1, m_SDiv(m_Value(X), m_Constant(C))) && match(Op0, m_Zero()) &&
-        !C->isMinSignedValue())
+        !C->isMinSignedValue() && !C->isOneValue())
       return BinaryOperator::CreateSDiv(X, ConstantExpr::getNeg(C));
 
     // 0 - (X << Y)  -> (-X << Y)   when X is freely negatable.