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llvm-project/clang/INPUTS/cfg-nested-var-scopes.cpp

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Enhance the CFG construction to detect no-return destructors for temporary objects and local variables. When detected, these split the block, marking the new one as having only the exit block as a successor. This prevents a large number of false positives in warnings sensitive to no-return constructs such as -Wreturn-type, and fixes the remainder of PR10063 along with several variations of this bug that had not been reported. The test cases are extended across the board to cover these patterns. This also checks in a stress test for these types of CFGs. The stress test declares some 32k variables, a mixture of no-return and normal destructors. Previously, this resulted in roughly 2500 CFG blocks, but didn't model any of the no-return destructors. With this patch, it results in over 33k blocks, many of them now unreachable. The nice thing about how the analyzer is set up? This causes *no* regression in performance of building the CFG. It actually in some cases makes it faster, as best I can benchmark. The analysis for -Wreturn-type (and any other that cares about no-return code paths) is technically slower now as it has to look at many more candidate blocks, but it computes the correct answer. I have more test cases to follow, I think they all work now. Also I have further work that should dramatically simplify analyses in the presence of no-return. llvm-svn: 139586
2011-09-13 14:09:01 +08:00
// Hammer the CFG with large numbers of overlapping variable scopes, which
// implicit destructors triggered at each edge.
#define EXPAND_BASIC_STRUCT(i) struct X##i { X##i(int); ~X##i(); };
#define EXPAND_NORET_STRUCT(i) struct X##i { X##i(int); ~X##i() __attribute__((noreturn)); };
EXPAND_BASIC_STRUCT(0000); EXPAND_NORET_STRUCT(0001);
EXPAND_BASIC_STRUCT(0010); EXPAND_BASIC_STRUCT(0011);
EXPAND_BASIC_STRUCT(0100); EXPAND_NORET_STRUCT(0101);
EXPAND_NORET_STRUCT(0110); EXPAND_BASIC_STRUCT(0111);
EXPAND_BASIC_STRUCT(1000); EXPAND_NORET_STRUCT(1001);
EXPAND_BASIC_STRUCT(1010); EXPAND_BASIC_STRUCT(1011);
EXPAND_NORET_STRUCT(1100); EXPAND_NORET_STRUCT(1101);
EXPAND_BASIC_STRUCT(1110); EXPAND_BASIC_STRUCT(1111);
#define EXPAND_2_VARS(c, i, x) const X##i var_##c##_##i##0(x), &var_##c##_##i##1 = X##i(x)
#define EXPAND_4_VARS(c, i, x) EXPAND_2_VARS(c, i##0, x); EXPAND_2_VARS(c, i##1, x)
#define EXPAND_8_VARS(c, i, x) EXPAND_4_VARS(c, i##0, x); EXPAND_4_VARS(c, i##1, x)
#define EXPAND_16_VARS(c, i, x) EXPAND_8_VARS(c, i##0, x); EXPAND_8_VARS(c, i##1, x)
#define EXPAND_32_VARS(c, x) EXPAND_16_VARS(c, 0, x); EXPAND_16_VARS(c, 1, x)
#define EXPAND_2_INNER_CASES(i, x, y) INNER_CASE(i, x, y); INNER_CASE(i + 1, x, y);
#define EXPAND_4_INNER_CASES(i, x, y) EXPAND_2_INNER_CASES(i, x, y) EXPAND_2_INNER_CASES(i + 2, x, y)
#define EXPAND_8_INNER_CASES(i, x, y) EXPAND_4_INNER_CASES(i, x, y) EXPAND_4_INNER_CASES(i + 4, x, y)
#define EXPAND_16_INNER_CASES(i, x, y) EXPAND_8_INNER_CASES(i, x, y) EXPAND_8_INNER_CASES(i + 8, x, y)
#define EXPAND_32_INNER_CASES(i, x, y) EXPAND_16_INNER_CASES(i, x, y) EXPAND_16_INNER_CASES(i + 16, x, y)
#define EXPAND_2_OUTER_CASES(i, x, y) OUTER_CASE(i, x, y); OUTER_CASE(i + 1, x, y);
#define EXPAND_4_OUTER_CASES(i, x, y) EXPAND_2_OUTER_CASES(i, x, y) EXPAND_2_OUTER_CASES(i + 2, x, y)
#define EXPAND_8_OUTER_CASES(i, x, y) EXPAND_4_OUTER_CASES(i, x, y) EXPAND_4_OUTER_CASES(i + 4, x, y)
#define EXPAND_16_OUTER_CASES(i, x, y) EXPAND_8_OUTER_CASES(i, x, y) EXPAND_8_OUTER_CASES(i + 8, x, y)
#define EXPAND_32_OUTER_CASES(i, x, y) EXPAND_16_OUTER_CASES(i, x, y) EXPAND_16_OUTER_CASES(i + 16, x, y)
unsigned cfg_nested_vars(int x) {
int y = 0;
while (x > 0) {
EXPAND_32_VARS(a, x);
switch (x) {
#define INNER_CASE(i, x, y) \
case i: { \
int case_var = 3*x + i; \
EXPAND_32_VARS(c, case_var); \
y += case_var - 1; \
break; \
}
#define OUTER_CASE(i, x, y) \
case i: { \
int case_var = y >> 8; \
EXPAND_32_VARS(b, y); \
switch (case_var) { \
EXPAND_32_INNER_CASES(0, x, y); \
} \
break; \
}
EXPAND_32_OUTER_CASES(0, x, y);
}
--x;
}
return y;
}