From: David Majnemer <david.majnemer@gmail.com>
Date: Mon, 14 Jul 2014 19:49:57 +0000 (+0000)
Subject: InstSimplify: The upper bound of X / C was missing a rounding step
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=7ceba3a1b0c9f3697740cbcbccc398927da055dc;p=oota-llvm.git

InstSimplify: The upper bound of X / C was missing a rounding step

Summary:
When calculating the upper bound of X / -8589934592, we would perform
the following calculation: Floor[INT_MAX / 8589934592]

However, flooring the result would make us wrongly come to the
conclusion that 1073741824 was not in the set of possible values.
Instead, use the ceiling of the result.

Reviewers: nicholas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D4502

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212976 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index bd42af15da3..1054c7935b5 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1964,7 +1964,15 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
       APInt Val = CI2->getValue().abs();
       if (!Val.isMinValue()) {
         Lower = IntMin.sdiv(Val);
-        Upper = IntMax.sdiv(Val) + 1;
+        APInt Rem;
+        APInt::sdivrem(IntMax, Val, Upper, Rem);
+        // We may need to round the result of the INT_MAX / CI2 calculation up
+        // if we see that the division was not exact.
+        if (Rem.isMinValue())
+          Upper = Upper + 1;
+        else
+          Upper = Upper + 2;
+        assert(Upper != Lower && "Upper part of range has wrapped!");
       }
     } else if (match(LHS, m_LShr(m_Value(), m_ConstantInt(CI2)))) {
       // 'lshr x, CI2' produces [0, UINT_MAX >> CI2].
diff --git a/test/Transforms/InstSimplify/compare.ll b/test/Transforms/InstSimplify/compare.ll
index 7d0cd9c5878..d329b7b719f 100644
--- a/test/Transforms/InstSimplify/compare.ll
+++ b/test/Transforms/InstSimplify/compare.ll
@@ -913,3 +913,14 @@ define i1 @icmp_sdiv_int_min(i32 %a) {
 ; CHECK-NEXT: [[CMP:%.*]] = icmp ne i32 [[DIV]], -1073741824
 ; CHECK-NEXT: ret i1 [[CMP]]
 }
+
+define i1 @icmp_sdiv_pr20288(i64 %a) {
+   %div = sdiv i64 %a, -8589934592
+   %cmp = icmp ne i64 %div, 1073741824
+   ret i1 %cmp
+
+; CHECK-LABEL: @icmp_sdiv_pr20288
+; CHECK-NEXT: [[DIV:%.*]] = sdiv i64 %a, -8589934592
+; CHECK-NEXT: [[CMP:%.*]] = icmp ne i64 [[DIV]], 1073741824
+; CHECK-NEXT: ret i1 [[CMP]]
+}