[clang] [clang][analyzer] Improved PointerSubChecker (PR #93676)

[Balazs Benics via cfe-commits]

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@@ -0,0 +1,74 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.core.PointerSub -verify %s
+
+void f1(void) {
+  int x, y, z[10];
+  int d = &y - &x; // expected-warning{{Subtraction of two pointers that do not point into the same array is undefined behavior}}
+  d = z - &y; // expected-warning{{Subtraction of two pointers that do not point into the same array is undefined behavior}}
+  d = &x - &x; // expected-warning{{Subtraction of two pointers that do not point into the same array is undefined behavior}}
+  d = (long*)&x - (long*)&x;
+}
+
+void f2(void) {
+  int a[10], b[10], c;
+  int *p = &a[2];
+  int *q = &a[8];
+  int d = q - p; // no-warning
+
+  q = &b[3];
+  d = q - p; // expected-warning{{Subtraction of two pointers that}}
+
+  q = a + 10;
+  d = q - p; // no warning (use of pointer to one after the end is allowed)
+  d = &a[4] - a; // no warning
+
+  q = a + 11;
+  d = q - a; // ?
+
+  d = &c - p; // expected-warning{{Subtraction of two pointers that}}
+}
+
+void f3(void) {
+  int a[3][4];
+  int d;
+
+  d = &(a[2]) - &(a[1]);
+  d = a[2] - a[1]; // expected-warning{{Subtraction of two pointers that}}
+  d = a[1] - a[1];
+  d = &(a[1][2]) - &(a[1][0]);
+  d = &(a[1][2]) - &(a[0][0]); // expected-warning{{Subtraction of two pointers that}}
+}
+
+void f4(void) {
+  int n = 4, m = 3;
+  int a[n][m];
+  int (*p)[m] = a; // p == &a[0]
+  p += 1; // p == &a[1]
+  int d = p - a; // d == 1 // expected-warning{{subtraction of pointers to type 'int[m]' of zero size has undefined behavior}}
+
+  d = &(a[2]) - &(a[1]); // expected-warning{{subtraction of pointers to type 'int[m]' of zero size has undefined behavior}}
+  d = a[2] - a[1]; // expected-warning{{Subtraction of two pointers that}}
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steakhal wrote:

Interestingly, clang's and gcc's constexpr interpreter accepts these lines, except for the last one. Who is right then?

https://github.com/llvm/llvm-project/pull/93676