From 2c73d5fb9e3d68c96bb2242bbbf2930a8db10343 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Sat, 25 Apr 2009 17:05:40 +0000
Subject: [PATCH] Handle ands with 0 and shifts by 0 correctly. These aren't
 common, but indvars shouldn't crash on them. This fixes PR4054.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70051 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp           | 11 +++++++++--
 test/Transforms/IndVarSimplify/avoid-i0.ll | 23 ++++++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 test/Transforms/IndVarSimplify/avoid-i0.ll

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 409bad91669..495290d8d73 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -1754,6 +1754,8 @@ SCEVHandle ScalarEvolution::createSCEV(Value *V) {
     // For an expression like x&255 that merely masks off the high bits,
     // use zext(trunc(x)) as the SCEV expression.
     if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) {
+      if (CI->isNullValue())
+        return getSCEV(U->getOperand(1));
       const APInt &A = CI->getValue();
       unsigned Ones = A.countTrailingOnes();
       if (APIntOps::isMask(Ones, A))
@@ -1818,10 +1820,15 @@ SCEVHandle ScalarEvolution::createSCEV(Value *V) {
       if (Instruction *L = dyn_cast<Instruction>(U->getOperand(0)))
         if (L->getOpcode() == Instruction::Shl &&
             L->getOperand(1) == U->getOperand(1)) {
-          uint64_t Amt = getTypeSizeInBits(U->getType()) - CI->getZExtValue();
+          unsigned BitWidth = getTypeSizeInBits(U->getType());
+          uint64_t Amt = BitWidth - CI->getZExtValue();
+          if (Amt == BitWidth)
+            return getSCEV(L->getOperand(0));       // shift by zero --> noop
+          if (Amt > BitWidth)
+            return getIntegerSCEV(0, U->getType()); // value is undefined
           return
             getSignExtendExpr(getTruncateExpr(getSCEV(L->getOperand(0)),
-                                                    IntegerType::get(Amt)),
+                                                      IntegerType::get(Amt)),
                                  U->getType());
         }
     break;
diff --git a/test/Transforms/IndVarSimplify/avoid-i0.ll b/test/Transforms/IndVarSimplify/avoid-i0.ll
new file mode 100644
index 00000000000..28112e75f55
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/avoid-i0.ll
@@ -0,0 +1,23 @@
+; RUN: llvm-as < %s | opt -indvars
+; PR4054
+
+; Don't treat an and with 0 as a mask (trunc+zext).
+
+define i32 @int80(i8 signext %p_71) nounwind {
+entry:
+	br label %bb
+
+bb:		; preds = %bb6, %entry
+	%p_71_addr.0 = phi i8 [ %p_71, %entry ], [ %0, %bb6 ]		; <i8> [#uses=0]
+	br i1 false, label %bb4, label %bb1
+
+bb1:		; preds = %bb
+	ret i32 0
+
+bb4:		; preds = %bb4, %bb
+	br i1 false, label %bb6, label %bb4
+
+bb6:		; preds = %bb4
+	%0 = and i8 0, 0		; <i8> [#uses=1]
+	br label %bb
+}
-- 
2.34.1