donat.nagy created this revision.
donat.nagy added reviewers: NoQ, george.karpenkov, rnkovacs,
baloghadamsoftware, mikhail.ramalho.
Herald added subscribers: cfe-commits, Szelethus.
Extend the alpha.core.Conversion checker to handle implicit converions
where a too large integer value is converted to a floating point type. Each
floating point type has a range where it can exactly represent all integers; we
emit a warning when the integer value is above this range. Although it is
possible to exactly represent some integers which are outside of this range
(those that are divisible by a large enough power of 2); we still report cast
involving those, because their usage may lead to bugs. (For example, if 1<<24
is stored in a float variable x, then x==x+1 holds.)
Repository:
rC Clang
https://reviews.llvm.org/D52730
Files:
lib/StaticAnalyzer/Checkers/ConversionChecker.cpp
test/Analysis/conversion.c
Index: test/Analysis/conversion.c
===================================================================
--- test/Analysis/conversion.c
+++ test/Analysis/conversion.c
@@ -137,6 +137,12 @@
U8 = S + 10;
}
+char dontwarn6(long long x) {
+ long long y=42;
+ y += x;
+ return y==42;
+}
+
// false positives..
@@ -181,3 +187,28 @@
}
}
+
+double floating_point(long long a, int b) {
+ if (a>1LL<<55) {
+ double r = a; // expected-warning {{Loss of precision}}
+ return r;
+ } else if (b>1<<25) {
+ float f = b; // expected-warning {{Loss of precision}}
+ return f;
+ }
+ return 137;
+}
+
+double floating_point2() {
+ int a = 1<<24;
+ long long b = 1LL<<53;
+ double d = a; // no-warning
+ double f = b; // no-warning
+ return d-f;
+}
+
+int floating_point_3(unsigned long long a) {
+ double b = a; // no-warning
+ return 42;
+}
+
Index: lib/StaticAnalyzer/Checkers/ConversionChecker.cpp
===================================================================
--- lib/StaticAnalyzer/Checkers/ConversionChecker.cpp
+++ lib/StaticAnalyzer/Checkers/ConversionChecker.cpp
@@ -14,8 +14,10 @@
// of expressions. A warning is reported when:
// * a negative value is implicitly converted to an unsigned value in an
// assignment, comparison or multiplication.
-// * assignment / initialization when source value is greater than the max
-// value of target
+// * assignment / initialization when the source value is greater than the max
+// value of the target integer type
+// * assignment / initialization when the source integer is above the range
+// where the target floating point type can represent all integers
//
// Many compilers and tools have similar checks that are based on semantic
// analysis. Those checks are sound but have poor precision. ConversionChecker
@@ -132,19 +134,65 @@
QualType SubType = Cast->IgnoreParenImpCasts()->getType();
- if (!DestType->isIntegerType() || !SubType->isIntegerType())
+ if (!DestType->isRealType() || !SubType->isIntegerType())
return false;
- if (C.getASTContext().getIntWidth(DestType) >=
- C.getASTContext().getIntWidth(SubType))
+ const bool isInteger = DestType->isIntegerType();
+
+ const auto &AC = C.getASTContext();
+
+ // We will find the largest RepresentsUntilExp value such that the DestType
+ // can exactly represent all integers 0 <= n < 2^RepresentsUntilExp
+ unsigned RepresentsUntilExp;
+
+ if (isInteger) {
+ RepresentsUntilExp = AC.getIntWidth(DestType);
+ if (RepresentsUntilExp == 1) {
+ // This is just casting a number to bool, probably not a bug.
+ return false;
+ }
+ if (DestType->isSignedIntegerType()) {
+ RepresentsUntilExp--;
+ }
+ } else {
+ unsigned FloatingSize = AC.getTypeSize(DestType);
+ switch (FloatingSize) {
+ case 64:
+ // double and possibly long double on some systems
+ RepresentsUntilExp = 53; break;
+ case 32:
+ // float
+ RepresentsUntilExp = 24; break;
+ case 16:
+ // _Float16
+ RepresentsUntilExp = 12; break;
+ default:
+ // larger types, which can represent all integers below 2^64
+ return false;
+ }
+ }
+
+ if (RepresentsUntilExp >= sizeof(unsigned long long)*8) {
return false;
+ }
+
+ unsigned CorrectedSrcWidth = AC.getIntWidth(SubType);
+ if (SubType->isSignedIntegerType()) {
+ CorrectedSrcWidth--;
+ }
- unsigned W = C.getASTContext().getIntWidth(DestType);
- if (W == 1 || W >= 64U)
+ if (RepresentsUntilExp >= CorrectedSrcWidth) {
+ // Simple case: the destination can store all values of the source type.
return false;
+ }
- unsigned long long MaxVal = 1ULL << W;
+ unsigned long long MaxVal = 1ULL << RepresentsUntilExp;
+ if (!isInteger) {
+ // if this is a floating point type, it can also represent MaxVal exactly
+ MaxVal++;
+ }
return C.isGreaterOrEqual(Cast->getSubExpr(), MaxVal);
+ // TODO: maybe also check negative values with too large magnitude
}
bool ConversionChecker::isLossOfSign(const ImplicitCastExpr *Cast,
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