7e5f9ead16
Whilst working on a backend patch, I noticed that the middle-end's RTL optimizers weren't simplifying a truncation of a paradoxical subreg extension, though it does transform closely related (more complex) expressions. The main (first) part of this patch implements this simplification, reusing much of the logic already in place. I briefly considered suggesting that it's difficult to provide a new testcase for this change, but then realized the reviewer's response would be that this type of transformation should be self-tested in simplify-rtx, so this patch adds a bunch of tests that integer extensions and truncations are simplified as expected. No good deed goes unpunished and I was equally surprised to see that we don't currently simplify/check/defend (zero_extend:SI (reg:SI)), i.e. useless no-op extensions to the same mode. So I've added some logic to simplify (or more accurately prevent us generating dubious RTL for) those. 2021-08-23 Roger Sayle <roger@nextmovesoftware.com> gcc/ChangeLog * simplify-rtx.c (simplify_truncation): Generalize simplification of (truncate:A (subreg:B X)). (simplify_unary_operation_1) [FLOAT_TRUNCATE, FLOAT_EXTEND, SIGN_EXTEND, ZERO_EXTEND]: Handle cases where the operand already has the desired machine mode. (test_scalar_int_ops): Add tests that useless extensions and truncations are optimized away. (test_scalar_int_ext_ops): New self-test function to confirm that truncations of extensions are correctly simplified. (test_scalar_int_ext_ops2): New self-test function to check truncations of truncations, extensions of extensions, and truncations of extensions. (test_scalar_ops): Call the above two functions with a representative sampling of integer machine modes. |
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