[LLVMbugs] [Bug 8636] New: clang chews through stack space

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=8636

           Summary: clang chews through stack space
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: chris at bubblescope.net
                CC: llvmbugs at cs.uiuc.edu


Been tracking down a memory exhaustion problem in automatically generated code
with clang which does not occur with gcc.

The following code shows our problem:

#include <stdio.h>

#define X1(x) if(i) { x } else { x }
#define X2(x) if(i) { x } else { x }
#define X3(x) if(i) { x } else { x }
#define X4(x) if(i) { x } else { x }
#define X5(x) if(i) { x } else { x }
#define X6(x) if(i) { x } else { x }
#define X7(x) if(i) { x } else { x }
#define X8(x) if(i) { x } else { x }
#define ARRAY { int x[4000]; printf("%ld\n", (y - x)); }
  void f(int i)
  {
int y[1];
X1(X2(X3(X4(X5(X6(X7(X8(ARRAY))))))));

  }

  int main(int argc, char** argv) {
    f(0);
  }

With no optimisation, gcc outputs 4000 while clang outputs 1024002. if I
increase the depth 2 more steps (the actual size we use in practice), a
clang-compiled executable just segfaults, while the gcc one works happily.

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