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fold-const: Fix ICE in fold_read_from_constant_string on invalid code [PR99204]

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fold_read_from_constant_string and expand_expr_real_1 have code to optimize
constant reads from string (tree vs. rtl).
If the STRING_CST array type has zero low bound, index is fold converted to
sizetype and so the compare_tree_int works fine, but if it has some other
low bound, it calls size_diffop_loc and that function from 2 sizetype
operands creates a ssizetype difference.  expand_expr_real_1 then uses
tree_fits_uhwi_p + compare_tree_int and so works fine, but fold-const.c
only checked if index is INTEGER_CST and calls compare_tree_int, which means
for negative index it will succeed and result in UB in the compiler.

2021-02-23  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/99204
	* fold-const.c (fold_read_from_constant_string): Check that
	tree_fits_uhwi_p (index) rather than just that index is INTEGER_CST.

	* gfortran.dg/pr99204.f90: New test.
This commit is contained in:
Jakub Jelinek 2021-02-23 09:49:48 +01:00
parent efa64fcce1
commit 37b64a3547
2 changed files with 11 additions and 1 deletions
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2
gcc/fold-const.c
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@ -15433,7 +15433,7 @@ fold_read_from_constant_string (tree exp)
if (string
&& TYPE_MODE (TREE_TYPE (exp)) == TYPE_MODE (TREE_TYPE (TREE_TYPE (string)))
&& TREE_CODE (string) == STRING_CST
&& TREE_CODE (index) == INTEGER_CST
&& tree_fits_uhwi_p (index)
&& compare_tree_int (index, TREE_STRING_LENGTH (string)) < 0
&& is_int_mode (TYPE_MODE (TREE_TYPE (TREE_TYPE (string))),
&char_mode)

10
gcc/testsuite/gfortran.dg/pr99204.f90 Normal file
View file

@ -0,0 +1,10 @@
! PR tree-optimization/99204
! { dg-do compile }
! { dg-options "-O2 -w" }
program pr99204
character :: c
integer :: i = -12345678
c = 'abc'(i:i)
print *, c
end