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| author | Eric Botcazou <ebotcazou@adacore.com> | 2023-05-29 09:45:57 +0200 |
|---|---|---|
| committer | Eric Botcazou <ebotcazou@adacore.com> | 2023-05-29 11:13:08 +0200 |
| commit | 3fa303becdc877a77e67e04401a50246dd05bd81 (patch) | |
| tree | 59900ba53dca1cb3243791b1ac1ac81f1f994ac8 | |
| parent | 6c2b2de098af7d3bf42126301438b70ad1279bcd (diff) | |
| download | gcc-3fa303becdc877a77e67e04401a50246dd05bd81.zip gcc-3fa303becdc877a77e67e04401a50246dd05bd81.tar.gz gcc-3fa303becdc877a77e67e04401a50246dd05bd81.tar.bz2 | |
Fix artificial overflow during GENERIC folding
The Ada compiler gives a bogus warning:
storage_offset1.ads:16:52: warning: Constraint_Error will be raised at run
time [enabled by default]
Ironically enough, this occurs because of an intermediate conversion to an
unsigned type which is supposed to hide overflows but is counter-productive
for constants because TREE_OVERFLOW is always set for them, so it ends up
setting a bogus TREE_OVERFLOW when converting back to the original type.
The fix simply redirects INTEGER_CSTs to the other, direct path without the
intermediate conversion to the unsigned type.
gcc/
* match.pd ((T)P - (T)(P + A) -> -(T) A): Avoid artificial overflow
on constants.
gcc/testsuite/
* gnat.dg/specs/storage_offset1.ads: New test.
| -rw-r--r-- | gcc/match.pd | 9 | ||||
| -rw-r--r-- | gcc/testsuite/gnat.dg/specs/storage_offset1.ads | 18 |
2 files changed, 27 insertions, 0 deletions
diff --git a/gcc/match.pd b/gcc/match.pd index 6e32f47..577f4ba 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -3194,6 +3194,13 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) (convert (plus:c @@0 @1))) (if (INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_UNDEFINED (type) + /* For integer literals, using an intermediate unsigned type to avoid + an overflow at run time is counter-productive because it introduces + spurious overflows at compile time, in the form of TREE_OVERFLOW on + the result, which may be problematic in GENERIC for some front-ends: + (T)P - (T)(P + 4) -> (T)(-(U)4) -> (T)(4294967292) -> -4(OVF) + so we use the direct path for them. */ + && TREE_CODE (@1) != INTEGER_CST && element_precision (type) <= element_precision (TREE_TYPE (@1))) (with { tree utype = unsigned_type_for (type); } (convert (negate (convert:utype @1)))) @@ -3213,6 +3220,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) (convert (pointer_plus @@0 @1))) (if (INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_UNDEFINED (type) + /* See above the rationale for this condition. */ + && TREE_CODE (@1) != INTEGER_CST && element_precision (type) <= element_precision (TREE_TYPE (@1))) (with { tree utype = unsigned_type_for (type); } (convert (negate (convert:utype @1)))) diff --git a/gcc/testsuite/gnat.dg/specs/storage_offset1.ads b/gcc/testsuite/gnat.dg/specs/storage_offset1.ads new file mode 100644 index 0000000..f0f7a61 --- /dev/null +++ b/gcc/testsuite/gnat.dg/specs/storage_offset1.ads @@ -0,0 +1,18 @@ +-- { dg-do compile } + +with System.Storage_Elements; use System.Storage_Elements; +with System; + +package Storage_Offset1 is + + type Rec is record + I1, I2 : Integer; + end record; + + type Ptr is access all Rec; + + R : Ptr := new Rec; + + Offset : constant Storage_Offset := R.I1'Address - R.I2'Address; + +end Storage_Offset1; |