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combine: Punt on out of range rotate counts [PR93505]

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What happens on this testcase is with the out of bounds rotate we get:
Trying 13 -> 16:
   13: r129:SI=r132:DI#0<-<0x20
      REG_DEAD r132:DI
   16: r123:DI=r129:SI<0
      REG_DEAD r129:SI
Successfully matched this instruction:
(set (reg/v:DI 123 [ <retval> ])
    (const_int 0 [0]))
during combine.  So, perhaps we could also change simplify-rtx.c to punt
if it is out of bounds rather than trying to optimize anything.
Or, but probably GCC11 material, if we decide that ROTATE/ROTATERT doesn't
have out of bounds counts or introduce targetm.rotate_truncation_mask,
we should truncate the argument instead of punting.
Punting is better for backports though.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/93505
	* combine.c (simplify_comparison) <case ROTATE>: Punt on out of range
	rotate counts.

	* gcc.c-torture/compile/pr93505.c: New test.
This commit is contained in:
Jakub Jelinek 2020-01-30 21:28:17 +01:00
parent 4dd468a042
commit 56b92750f8
4 changed files with 28 additions and 1 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2020-01-30 Jakub Jelinek <jakub@redhat.com>
PR middle-end/93505
* combine.c (simplify_comparison) <case ROTATE>: Punt on out of range
rotate counts.
2020-01-30 Andrew Stubbs <ams@codesourcery.com>
* config/gcn/gcn.c (print_operand): Handle LTGT.

3
gcc/combine.c
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@ -12410,7 +12410,8 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
bit. This will be converted into a ZERO_EXTRACT. */
if (const_op == 0 && sign_bit_comparison_p
&& CONST_INT_P (XEXP (op0, 1))
&& mode_width <= HOST_BITS_PER_WIDE_INT)
&& mode_width <= HOST_BITS_PER_WIDE_INT
&& UINTVAL (XEXP (op0, 1)) < mode_width)
{
op0 = simplify_and_const_int (NULL_RTX, mode, XEXP (op0, 0),
(HOST_WIDE_INT_1U

5
gcc/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2020-01-30 Jakub Jelinek <jakub@redhat.com>
PR middle-end/93505
* gcc.c-torture/compile/pr93505.c: New test.
2020-01-30 Jeff Law <law@redhat.com
* gcc.dg/tree-ssa/ssa-dse-26.c: Make existing dg-final scan

15
gcc/testsuite/gcc.c-torture/compile/pr93505.c Normal file
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@ -0,0 +1,15 @@
/* PR middle-end/93505 */
unsigned a;
unsigned
foo (unsigned x)
{
unsigned int y = 32 - __builtin_bswap64 (-a);
/* This would be UB (x << 32) at runtime. Ensure we don't
invoke UB in the compiler because of that (visible with
bootstrap-ubsan). */
x = x << y | x >> (-y & 31);
x >>= 31;
return x;
}