From 43b40a4620c155c73ac71b48472ea2411d7c35da Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Tue, 4 Jan 2011 18:19:15 +0000
Subject: [PATCH] fix an off-by-one bug that caused a crash analyzing ashr's
 with huge shift amounts, PR8896

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122814 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ValueTracking.cpp       |  2 +-
 test/Transforms/InstCombine/crash.ll | 37 ++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 6f58afe5279..e2d7e9290ab 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -337,7 +337,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     // (ashr X, C1) & C2 == 0   iff  (-1 >> C1) & C2 == 0
     if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
       // Compute the new bits that are at the top now.
-      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
+      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
       
       // Signed shift right.
       APInt Mask2(Mask.shl(ShiftAmt));
diff --git a/test/Transforms/InstCombine/crash.ll b/test/Transforms/InstCombine/crash.ll
index deb7277c5e5..60cb7477879 100644
--- a/test/Transforms/InstCombine/crash.ll
+++ b/test/Transforms/InstCombine/crash.ll
@@ -298,3 +298,40 @@ entry:
 }
 
 
+; PR8896
+@g_54 = external global [7 x i16]
+
+define void @test15(i32* %p_92) nounwind {
+entry:
+%0 = load i32* %p_92, align 4
+%1 = icmp ne i32 %0, 0
+%2 = zext i1 %1 to i32
+%3 = call i32 @func_14() nounwind
+%4 = trunc i32 %3 to i16
+%5 = sext i16 %4 to i32
+%6 = trunc i32 %5 to i16
+br i1 undef, label %"3", label %"5"
+
+"3":                                              ; preds = %entry
+%7 = sext i16 %6 to i32
+%8 = ashr i32 %7, -1649554541
+%9 = trunc i32 %8 to i16
+br label %"5"
+
+"5":                                              ; preds = %"3", %entry
+%10 = phi i16 [ %9, %"3" ], [ %6, %entry ]
+%11 = sext i16 %10 to i32
+%12 = xor i32 %2, %11
+%13 = sext i32 %12 to i64
+%14 = icmp ne i64 %13, 0
+br i1 %14, label %return, label %"7"
+
+"7":                                              ; preds = %"5"
+ret void
+
+return:                                           ; preds = %"5"
+ret void
+}
+
+declare i32 @func_14()
+