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PR rtl-optimization 61494: Preserve x-0.0 with HONOR_SNANS.

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The following patch avoids simplifying x-0.0 to x when -fsignaling-nans
is specified, which resolves PR rtl-optimization 61494.  Indeed, running
the test program attached to that PR now reports no failures.

2020-08-02  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR rtl-optimization/61494
	* simplify-rtx.c (simplify_binary_operation_1) [MINUS]: Don't
	simplify x - 0.0 with -fsignaling-nans.
This commit is contained in:
Roger Sayle 2020-08-03 13:15:58 +01:00
parent ef59e1fb37
commit 919c9d4bd3
1 changed files with 4 additions and 3 deletions
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gcc/simplify-rtx.c
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@ -2678,11 +2678,12 @@ simplify_binary_operation_1 (enum rtx_code code, machine_mode mode,
&& !contains_symbolic_reference_p (op1))
return simplify_gen_unary (NOT, mode, op1, mode);
/* Subtracting 0 has no effect unless the mode has signed zeros
and supports rounding towards -infinity. In such a case,
0 - 0 is -0. */
/* Subtracting 0 has no effect unless the mode has signalling NaNs,
or has signed zeros and supports rounding towards -infinity.
In such a case, 0 - 0 is -0. */
if (!(HONOR_SIGNED_ZEROS (mode)
&& HONOR_SIGN_DEPENDENT_ROUNDING (mode))
&& !HONOR_SNANS (mode)
&& trueop1 == CONST0_RTX (mode))
return op0;