InstSimplify: Fix a bug when INT_MIN is in a sdiv

When INT_MIN is the numerator in a sdiv, we would not properly handle
overflow when calculating the bounds of possible values; abs(INT_MIN) is
not a meaningful number.

Instead, check and handle INT_MIN by reasoning that the largest value is
INT_MIN/-2 and the smallest value is INT_MIN.

This fixes PR20199.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212307 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 31263bb7de89226f05e062a29a442bf0dac0a064..bd42af15da311f222757ad470d7fc647d367de7e 100644 (file)
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1948,9 +1948,15 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
       if (!CI2->isZero())
         Upper = NegOne.udiv(CI2->getValue()) + 1;
     } else if (match(LHS, m_SDiv(m_ConstantInt(CI2), m_Value()))) {
-      // 'sdiv CI2, x' produces [-|CI2|, |CI2|].
-      Upper = CI2->getValue().abs() + 1;
-      Lower = (-Upper) + 1;
+      if (CI2->isMinSignedValue()) {
+        // 'sdiv INT_MIN, x' produces [INT_MIN, INT_MIN / -2].
+        Lower = CI2->getValue();
+        Upper = Lower.lshr(1) + 1;
+      } else {
+        // 'sdiv CI2, x' produces [-|CI2|, |CI2|].
+        Upper = CI2->getValue().abs() + 1;
+        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);

diff --git a/test/Transforms/InstSimplify/compare.ll b/test/Transforms/InstSimplify/compare.ll
index 89fd6362d78d2c2d243cbf7399473d2a65352664..7d0cd9c58783751a69016d9a6dd3d9bfc18937ad 100644 (file)
--- a/test/Transforms/InstSimplify/compare.ll
+++ b/test/Transforms/InstSimplify/compare.ll
@@ -902,3 +902,14 @@ define i1 @icmp_ne_const(i32 %a) nounwind {
 ; CHECK-LABEL: @icmp_ne_const
 ; CHECK-NEXT: ret i1 true
 }
+
+define i1 @icmp_sdiv_int_min(i32 %a) {
+  %div = sdiv i32 -2147483648, %a
+  %cmp = icmp ne i32 %div, -1073741824
+  ret i1 %cmp
+
+; CHECK-LABEL: @icmp_sdiv_int_min
+; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 -2147483648, %a
+; CHECK-NEXT: [[CMP:%.*]] = icmp ne i32 [[DIV]], -1073741824
+; CHECK-NEXT: ret i1 [[CMP]]
+}