[LLVMbugs] [Bug 22899] New: false negative of -Winteger-overflow

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Fri Mar 13 16:54:25 PDT 2015


            Bug ID: 22899
           Summary: false negative of -Winteger-overflow
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: chengniansun at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Clang warns on integer overflow in variable initialization but not assignment.
For example, there is warning on 
  int a = ((uint16_t)0xE570L * (uint16_t)(-1L));
But if I split the statement into two, Clang will not warn:
  int b; 
  b = ((uint16_t)0xE570L * (uint16_t)(-1L));

$: cat t.c
#include <stdint.h>
int main(void) {
  int a = ((uint16_t)0xE570L * (uint16_t)(-1L));
  int b; 
  b = ((uint16_t)0xE570L * (uint16_t)(-1L));
  return 0;
$: clang-trunk -Wconversion t.c
t.c:3:30: warning: overflow in expression; result is -445703536 with type 'int'
  int a = ((uint16_t)0xE570L * (uint16_t)(-1L));
1 warning generated.
$: gcc-trunk -Wconversion t.c
t.c: In function ‘main’:
t.c:3:30: warning: integer overflow in expression [-Woverflow]
   int a = ((uint16_t)0xE570L * (uint16_t)(-1L));
t.c:5:26: warning: integer overflow in expression [-Woverflow]
   b = ((uint16_t)0xE570L * (uint16_t)(-1L));

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