[PATCH] PR tree-optimization/96392 Optimize x+0.0 if x is an integer

The patch implements a missed optimization enhancement.  Under usual
IEEE rules, x+0.0 can't be simplified to x when x might potentially
be an IEEE minus zero (-0.0).  The current logic in the middle-end
checks whether the type of x should honor signed zeros, but with this
patch we introduce tree_expr_maybe_real_minus_zero_p that allows us
to confirm that the value can't possibly be -0.0, for example, the result
of a conversion from an integer type, or the result of fabs (or has a
type that doesn't honor signed zero).

Whilst modifying match.pd, I also converted some additional folding
transformations from "testing the type" to "testing the value".

2020-06-10  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR tree-optimization/96392
	* fold-const.c (fold_real_zero_addition_p): Take both arguments
	of the addition or subtraction, not just the zero.  Use this
	other argument in tests for signaling NaNs and signed zeros.
	(tree_expr_maybe_real_minus_zero_p): New predicate.
	* fold-const.h (fold_real_zero_addition_p): Update prototype.
	(tree_expr_maybe_real_minus_zero_p): New function prototype.
	* match.pd: Update calls to fold_real_zero_addition_p.
	Replace HONOR_NANS with tree_expr_maybe_nan_p.
	Replace HONOR_SIGNED_ZEROS with tree_expr_maybe_real_minus_zero_p.
	Replace HONOR_SNANS with tree_expr_maybe_signaling_nan_p.
	* tree-ssa-reassoc.c (eliminate_using_constants): Update
	call to fold_real_zero_addition_p.

gcc/testsuite/ChangeLog
	PR tree-optimization/96392
	* gcc.dg/pr96392.c: New test.

0 files changed, 0 insertions, 0 deletions