InstSimplify: Correct sdiv x / -1

Determining the bounds of x/ -1 would start off with us dividing it by
INT_MIN.  Suffice to say, this would not work very well.

Instead, handle it upfront by checking for -1 and mapping it to the
range: [INT_MIN + 1, INT_MAX.  This means that the result of our
division can be any value other than INT_MIN.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212981 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 1054c7935b5c581f2b3782657e6a07b087cf90dc..fd7a4de6903786b7ef7c44093799a1a0c57bb32c 100644 (file)
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1958,20 +1958,22 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
         Lower = (-Upper) + 1;
       }
     } else if (match(LHS, m_SDiv(m_Value(), m_ConstantInt(CI2)))) {
-      // 'sdiv x, CI2' produces [INT_MIN / CI2, INT_MAX / CI2].
       APInt IntMin = APInt::getSignedMinValue(Width);
       APInt IntMax = APInt::getSignedMaxValue(Width);
-      APInt Val = CI2->getValue().abs();
-      if (!Val.isMinValue()) {
+      APInt Val = CI2->getValue();
+      if (Val.isAllOnesValue()) {
+        // 'sdiv x, -1' produces [INT_MIN + 1, INT_MAX]
+        //    where CI2 != -1 and CI2 != 0 and CI2 != 1
+        Lower = IntMin + 1;
+        Upper = IntMax + 1;
+      } else if (Val.countLeadingZeros() < Width - 1) {
+        // 'sdiv x, CI2' produces [INT_MIN / CI2, INT_MAX / CI2]
+        //    where CI2 != -1 and CI2 != 0 and CI2 != 1
         Lower = IntMin.sdiv(Val);
-        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;
+        Upper = IntMax.sdiv(Val);
+        if (Lower.sgt(Upper))
+          std::swap(Lower, Upper);
+        Upper = Upper + 1;
         assert(Upper != Lower && "Upper part of range has wrapped!");
       }
     } else if (match(LHS, m_LShr(m_Value(), m_ConstantInt(CI2)))) {

diff --git a/test/Transforms/InstSimplify/compare.ll b/test/Transforms/InstSimplify/compare.ll
index d329b7b719f8a0bd6dc65cd31377da7eec889e1b..1a9f82e9f4217310a59e71090dd740148b46b01a 100644 (file)
--- a/test/Transforms/InstSimplify/compare.ll
+++ b/test/Transforms/InstSimplify/compare.ll
@@ -924,3 +924,14 @@ define i1 @icmp_sdiv_pr20288(i64 %a) {
 ; CHECK-NEXT: [[CMP:%.*]] = icmp ne i64 [[DIV]], 1073741824
 ; CHECK-NEXT: ret i1 [[CMP]]
 }
+
+define i1 @icmp_sdiv_neg1(i64 %a) {
+ %div = sdiv i64 %call, -1
+ %cmp = icmp ne i64 %div, 1073741824
+ ret i1 %cmp
+
+; CHECK-LABEL: @icmp_sdiv_neg1
+; CHECK-NEXT: [[DIV:%.*]] = sdiv i64 %a, -1
+; CHECK-NEXT: [[CMP:%.*]] = icmp ne i64 [[DIV]], 1073741824
+; CHECK-NEXT: ret i1 [[CMP]]
+}