On 26/04/17 13:39, Wilco Dijkstra wrote:
> Float to int moves currently generate inefficient code due to
> hacks used in the movsi and movdi patterns. The 'r = w' variant
> uses '*' which explicitly tells the register allocator to ignore it.
> As a result float to int moves typically spill to the stack, which is
> extremely inefficient. For example:
>
> static inline unsigned asuint (float f)
> {
> union { float f; unsigned i; } u = {f};
> return u.i;
> }
>
> float foo (float x)
> {
> unsigned i = asuint (x);
> if (__builtin_expect (i > 42, 0))
> return x*x;
> return i;
> }
>
> generates:
>
> sub sp, sp, #16
> str s0, [sp, 12]
> ldr w0, [sp, 12]
> cmp w0, 42
> bhi .L7
> scvtf s0, w0
> add sp, sp, 16
> ret
> .L7:
> fmul s0, s0, s0
> add sp, sp, 16
> ret
>
> Removing '*' from the variant generates:
>
> fmov w0, s0
> cmp w0, 42
> bhi .L6
> scvtf s0, w0
> ret
> .L6:
> fmul s0, s0, s0
> ret
>
> Passes regress & bootstrap, OK for commit?
>
> ChangeLog:
> 2017-04-26 Wilco Dijkstra <[email protected]>
>
> * config/aarch64/aarch64.md (movsi_aarch64): Remove '*' from r=w.
> (movdi_aarch64): Likewise.
>
OK.
While on the subject, why is the w->w operation also hidden?
R.
> --
> diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
> index
> 51368e29f2d1fd12f48a972bd81a08589a720e07..d656e92e1ff02bdc90c824227ec3b2e1ccfe665a
> 100644
> --- a/gcc/config/aarch64/aarch64.md
> +++ b/gcc/config/aarch64/aarch64.md
> @@ -1026,8 +1026,8 @@ (define_expand "mov<mode>"
> )
>
> (define_insn_and_split "*movsi_aarch64"
> - [(set (match_operand:SI 0 "nonimmediate_operand" "=r,k,r,r,r,r,*w,m,
> m,r,r ,*w, r,*w")
> - (match_operand:SI 1 "aarch64_mov_operand" " r,r,k,M,n,m,
> m,rZ,*w,S,Ush,rZ,*w,*w"))]
> + [(set (match_operand:SI 0 "nonimmediate_operand" "=r,k,r,r,r,r,*w,m,
> m,r,r ,*w,r,*w")
> + (match_operand:SI 1 "aarch64_mov_operand" " r,r,k,M,n,m,
> m,rZ,*w,S,Ush,rZ,w,*w"))]
> "(register_operand (operands[0], SImode)
> || aarch64_reg_or_zero (operands[1], SImode))"
> "@
> @@ -1058,8 +1058,8 @@ (define_insn_and_split "*movsi_aarch64"
> )
>
> (define_insn_and_split "*movdi_aarch64"
> - [(set (match_operand:DI 0 "nonimmediate_operand" "=r,k,r,r,r,r,*w,m,
> m,r,r, *w, r,*w,w")
> - (match_operand:DI 1 "aarch64_mov_operand" " r,r,k,N,n,m,
> m,rZ,*w,S,Ush,rZ,*w,*w,Dd"))]
> + [(set (match_operand:DI 0 "nonimmediate_operand" "=r,k,r,r,r,r,*w,m,
> m,r,r, *w,r,*w,w")
> + (match_operand:DI 1 "aarch64_mov_operand" " r,r,k,N,n,m,
> m,rZ,*w,S,Ush,rZ,w,*w,Dd"))]
> "(register_operand (operands[0], DImode)
> || aarch64_reg_or_zero (operands[1], DImode))"
> "@
>
