[PATCH] D140086: [analyzer][solver] Improve reasoning for not equal to operator

[Manas Gupta via Phabricator via cfe-commits]

manas updated this revision to Diff 486425.
manas added a comment.

Re-introduce bitwidth comparison


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D140086/new/

https://reviews.llvm.org/D140086

Files:
  clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
  clang/test/Analysis/constant-folding.c


Index: clang/test/Analysis/constant-folding.c
===================================================================
--- clang/test/Analysis/constant-folding.c
+++ clang/test/Analysis/constant-folding.c
@@ -303,7 +303,8 @@
 
   if (s1 < 0 && s1 > -4 && u1 > UINT_MAX - 4 && u1 < UINT_MAX - 1) {
     // s1: [-3, -1], u1: [UINT_MAX - 3, UINT_MAX - 2]
-    clang_analyzer_eval(u1 != s1); // expected-warning{{UNKNOWN}}
+    clang_analyzer_eval(u1 != s1); // expected-warning{{TRUE}}
+    clang_analyzer_eval(s1 != u1); // expected-warning{{TRUE}}
   }
 
   if (s1 < 1 && s1 > -6 && s1 != -4 && s1 != -3 &&
@@ -400,12 +401,10 @@
     clang_analyzer_eval(uch != sch); // expected-warning{{UNKNOWN}}
   }
 
-  // FIXME: Casting smaller signed types to unsigned one may leave us with
-  // overlapping values, falsely indicating UNKNOWN, where it is possible to
-  // assert TRUE.
   if (uch > 1 && sch < 1) {
     // uch: [2, UCHAR_MAX], sch: [SCHAR_MIN, 0]
-    clang_analyzer_eval(uch != sch); // expected-warning{{UNKNOWN}}
+    clang_analyzer_eval(uch != sch); // expected-warning{{TRUE}}
+    clang_analyzer_eval(sch != uch); // expected-warning{{TRUE}}
   }
 
   if (uch <= 1 && uch >= 1 && sch <= 1 && sch >= 1) {
@@ -419,10 +418,9 @@
     clang_analyzer_eval(ush != ssh); // expected-warning{{UNKNOWN}}
   }
 
-  // FIXME: Casting leave us with overlapping values. Should be TRUE.
   if (ush > 1 && ssh < 1) {
     // ush: [2, USHRT_MAX], ssh: [SHRT_MIN, 0]
-    clang_analyzer_eval(ush != ssh); // expected-warning{{UNKNOWN}}
+    clang_analyzer_eval(ush != ssh); // expected-warning{{TRUE}}
   }
 
   if (ush <= 1 && ush >= 1 && ssh <= 1 && ssh >= 1) {
Index: clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
===================================================================
--- clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
+++ clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
@@ -1619,7 +1619,33 @@
   if (LHS.getAPSIntType() == RHS.getAPSIntType()) {
     if (intersect(RangeFactory, LHS, RHS).isEmpty())
       return getTrueRange(T);
+
   } else {
+    // We can only lose information if we are casting smaller signed type to
+    // bigger unsigned type. For e.g.,
+    //    LHS (unsigned short): [2, USHRT_MAX]
+    //    RHS   (signed short): [SHRT_MIN, 0]
+    //
+    // Casting RHS to LHS type will leave us with overlapping values
+    //    CastedRHS : [0, 0] U [SHRT_MAX + 1, USHRT_MAX]
+    //
+    // We can avoid this by checking if signed type's maximum value is lesser
+    // than unsigned type's minimum value.
+
+    // If both have different signs then only we can get more information.
+    if (LHS.isUnsigned() != RHS.isUnsigned()) {
+      if (LHS.isUnsigned() && (LHS.getBitWidth() >= RHS.getBitWidth())) {
+        if (RHS.getMaxValue().isNegative() ||
+            LHS.getAPSIntType().convert(RHS.getMaxValue()) < LHS.getMinValue())
+          return getTrueRange(T);
+
+      } else if (RHS.isUnsigned() && (LHS.getBitWidth() <= RHS.getBitWidth())) {
+        if (LHS.getMaxValue().isNegative() ||
+            RHS.getAPSIntType().convert(LHS.getMaxValue()) < RHS.getMinValue())
+          return getTrueRange(T);
+      }
+    }
+
     // Both RangeSets should be casted to bigger unsigned type.
     APSIntType CastingType(std::max(LHS.getBitWidth(), RHS.getBitWidth()),
                            LHS.isUnsigned() || RHS.isUnsigned());
@@ -2148,7 +2174,6 @@
   RangeSet::Factory &RangeFactory;
 };
 
-
 bool ConstraintAssignor::assignSymExprToConst(const SymExpr *Sym,
                                               const llvm::APSInt &Constraint) {
   llvm::SmallSet<EquivalenceClass, 4> SimplifiedClasses;


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