[compiler-rt][ubsan] Refactor cast-overflow test

[alexander-shaposhnikov]

This PR cleans up cast-overflow.cpp, more specifically:

1. avoid using undefined value as an exit code (old case 9)
2. narrowing conversions are allowed to produce inf and they are well-defined. Remove dead code (old case 8)
3. the same applies to the conversion int -> float16. Remove dead code (old case 7)

See also https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#:~:text=%2Dfsanitize%3Dfloat%2Dcast,to%20integer%20types.

Currently ubsan doesn't properly detect UB on float16 -> int casts, I have a fix for that (will send as a separate PR).

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Alexander Shaposhnikov (alexander-shaposhnikov)

Changes

This PR cleans up cast-overflow.cpp, more specifically:

1. avoid using undefined value as an exit code (old case 9)
2. narrowing conversions are allowed to produce inf and they are well-defined. Remove dead code (old case 8)
3. the same applies to the conversion int -> float16. Remove dead code (old case 7)

Currently ubsan doesn't properly detect UB on float16 -> int casts, I have a fix for that (will send as a separate PR).

---

Full diff: https://github.com/llvm/llvm-project/pull/129460.diff

1 Files Affected:

• (modified) compiler-rt/test/ubsan/TestCases/Float/cast-overflow.cpp (+7-17)

diff --git a/compiler-rt/test/ubsan/TestCases/Float/cast-overflow.cpp b/compiler-rt/test/ubsan/TestCases/Float/cast-overflow.cpp
index 4daa96c676c30..8ec71261013d6 100644
--- a/compiler-rt/test/ubsan/TestCases/Float/cast-overflow.cpp
+++ b/compiler-rt/test/ubsan/TestCases/Float/cast-overflow.cpp
@@ -7,9 +7,7 @@
 // RUN: %run %t 4 2>&1 | FileCheck %s --check-prefix=CHECK-4
 // RUN: %run %t 5 2>&1 | FileCheck %s --check-prefix=CHECK-5
 // RUN: %run %t 6 2>&1 | FileCheck %s --check-prefix=CHECK-6
-// FIXME: %run %t 7 2>&1 | FileCheck %s --check-prefix=CHECK-7
-// FIXME: not %run %t 8 2>&1 | FileCheck %s --check-prefix=CHECK-8
-// RUN: not %run %t 9 2>&1 | FileCheck %s --check-prefix=CHECK-9
+// RUN: %run %t 7 2>&1 | FileCheck %s --check-prefix=CHECK-7
 
 // Issue #41838
 // XFAIL: sparc-target-arch && target={{.*solaris.*}}
@@ -151,20 +149,12 @@ int main(int argc, char **argv) {
     return 0;
 #endif
   }
-  // FIXME: The backend cannot lower __fp16 operations on x86 yet.
-  //case '7':
-  //  (__fp16)65504; // ok
-  //  // CHECK-7: runtime error: 65505 is outside the range of representable values of type '__fp16'
-  //  return (__fp16)65505;
-
-    // Floating point -> floating point overflow.
-  case '8':
-    // CHECK-8: {{.*}}cast-overflow.cpp:[[@LINE+1]]:19: runtime error: 1e+39 is outside the range of representable values of type 'float'
-    return (float)1e39;
-  case '9':
+  case '7': {
     volatile long double ld = 300.0;
-    // CHECK-9: {{.*}}cast-overflow.cpp:[[@LINE+1]]:14: runtime error: 300 is outside the range of representable values of type 'char'
+    // CHECK-7: {{.*}}cast-overflow.cpp:[[@LINE+1]]:14: runtime error: 300 is outside the range of representable values of type 'char'
     char c = ld;
-    return c;
-  }
+    // `c` is allowed to contain UNDEF, thus we should not use
+    // its value as an exit code.
+    return 0;
+  }}
 }

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