Hello, On Tue, 20 Jun 2023, Jakub Jelinek via Gcc wrote:
> ce1 pass results in emit_conditional_move with > (gt (reg/v:SF 83 [ x ]) (reg:SF 84)), (reg/v:SF 83 [ x ]), (reg:SF 84) > operands in the GCC 11 case and so is successfully matched by > ix86_expand_fp_movcc as ix86_expand_sse_fp_minmax. > But, in GCC 12+, emit_conditional_move is called with > (gt (reg/v:SF 83 [ x ]) (reg:SF 84)), (reg/v:SF 83 [ x ]), (const_double:SF > 0.0 [0x0.0p+0]) > instead (reg:SF 84 in both cases contains the (const_double:SF 0.0 [0x0.0p+0]) > value, in the GCC 11 case loaded from memory, in the GCC 12+ case set > directly in a move. The reason for the difference is exactly that > because cheap SSE constant can be moved directly into a reg, it is done so > instead of reusing a pseudo that contains that value already. But reg84 is _also_ used as operand of emit_conditional_move, so there's no reason to not also use it as third operand. It seems more canonical to call a function with X-containing-B, A, B than with X-containing-B, A, something-equal-to-B-but-not-B so either the (const_double) RTL should be used in both, or reg84 should, but not a mix. Exactly so to ... > actually a minmax. Even if it allowed the cheap SSE constants, > it wouldn't know that r84 is also zero (unless the expander checks that > it is a pseudo with a single setter and verifies it or something similar). ... not have this problem. Ciao, Michael.
