On Thu, 1 Dec 2016, Paolo Bonzini wrote:
> In code like the following from KVM:
>
> /* it is a read fault? */
> error_code = (exit_qualification << 2) & PFERR_FETCH_MASK;
>
> it would be nicer to write
>
> /* it is a read fault? */
> error_code = (exit_qualification & VMX_EPT_READ_FAULT_MASK) ?
> PFERR_FETCH_MASK : 0;
>
> instead of having to know the difference between the positions of the
> source and destination bits. LLVM catches the latter just fine (which
> is why I am sending this in stage 3...), but GCC does not, so this
> patch adds two patterns to catch it.
>
> The combine.c hunk of v1 has been committed already.
>
> Bootstrapped/regtested x86_64-pc-linux-gnu, ok?
Ok.
Thanks,
Richard.
> Paolo
>
> 2016-11-26 Paolo Bonzini <bonz...@gnu.org>
>
> * match.pd: Simplify X ? C : 0 where C is a power of 2 and
> X tests a single bit.
>
> 2016-11-26 Paolo Bonzini <bonz...@gnu.org>
>
> * gcc.dg/fold-and-lshift.c, gcc.dg/fold-and-rshift-1.c,
> gcc.dg/fold-and-rshift-2.c: New testcases.
>
> Index: match.pd
> ===================================================================
> --- match.pd (revision 242916)
> +++ match.pd (working copy)
> @@ -2630,6 +2630,21 @@
> (cmp (bit_and@2 @0 integer_pow2p@1) @1)
> (icmp @2 { build_zero_cst (TREE_TYPE (@0)); })))
>
> +/* If we have (A & C) != 0 ? D : 0 where C and D are powers of 2,
> + convert this into a shift followed by ANDing with D. */
> +(simplify
> + (cond
> + (ne (bit_and @0 integer_pow2p@1) integer_zerop)
> + integer_pow2p@2 integer_zerop)
> + (with {
> + int shift = wi::exact_log2 (@2) - wi::exact_log2 (@1);
> + }
> + (if (shift > 0)
> + (bit_and
> + (lshift (convert @0) { build_int_cst (integer_type_node, shift); }) @2)
> + (bit_and
> + (convert (rshift @0 { build_int_cst (integer_type_node, -shift); }))
> @2))))
> +
> /* If we have (A & C) != 0 where C is the sign bit of A, convert
> this into A < 0. Similarly for (A & C) == 0 into A >= 0. */
> (for cmp (eq ne)
> @@ -2644,6 +2659,19 @@
> (with { tree stype = signed_type_for (TREE_TYPE (@0)); }
> (ncmp (convert:stype @0) { build_zero_cst (stype); })))))
>
> +/* If we have A < 0 ? C : 0 where C is a power of 2, convert
> + this into a right shift followed by ANDing with C. */
> +(simplify
> + (cond
> + (lt @0 integer_zerop)
> + integer_pow2p@1 integer_zerop)
> + (with {
> + int shift = element_precision (@0) - wi::exact_log2 (@1) - 1;
> + }
> + (bit_and
> + (convert (rshift @0 { build_int_cst (integer_type_node, shift); }))
> + @1)))
> +
> /* When the addresses are not directly of decls compare base and offset.
> This implements some remaining parts of fold_comparison address
> comparisons but still no complete part of it. Still it is good
> Index: testsuite/gcc.dg/fold-and-lshift.c
> ===================================================================
> --- testsuite/gcc.dg/fold-and-lshift.c (revision 0)
> +++ testsuite/gcc.dg/fold-and-lshift.c (working copy)
> @@ -0,0 +1,35 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-original" } */
> +
> +int f(int x)
> +{
> + return (x << 2) & 128;
> +}
> +
> +int g(int x)
> +{
> + return !!(x & 32) << 7;
> +}
> +
> +int h(int x)
> +{
> + return ((x >> 5) & 1) << 7;
> +}
> +
> +int i(int x)
> +{
> + return (x & 32) >> 5 << 7;
> +}
> +
> +int j(int x)
> +{
> + return ((x >> 5) & 1) ? 128 : 0;
> +}
> +
> +int k(int x)
> +{
> + return (x & 32) ? 128 : 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-not " \\? " "original" } } */
> +/* { dg-final { scan-assembler-not "sarl" { target i?86-*-* x86_64-*-* } }
> }" */
> Index: testsuite/gcc.dg/fold-and-rshift-1.c
> ===================================================================
> --- testsuite/gcc.dg/fold-and-rshift-1.c (revision 0)
> +++ testsuite/gcc.dg/fold-and-rshift-1.c (working copy)
> @@ -0,0 +1,35 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-original" } */
> +
> +int f(int x)
> +{
> + return (x >> 2) & 128;
> +}
> +
> +int g(int x)
> +{
> + return !!(x & 512) << 7;
> +}
> +
> +int h(int x)
> +{
> + return ((x >> 9) & 1) << 7;
> +}
> +
> +int i(int x)
> +{
> + return (x & 512) >> 9 << 7;
> +}
> +
> +int j(int x)
> +{
> + return ((x >> 9) & 1) ? 128 : 0;
> +}
> +
> +int k(int x)
> +{
> + return (x & 512) ? 128 : 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-not " \\? " "original" } } */
> +/* { dg-final { scan-assembler-not "sall" { target i?86-*-* x86_64-*-* } }
> }" */
> Index: testsuite/gcc.dg/fold-and-rshift-2.c
> ===================================================================
> --- testsuite/gcc.dg/fold-and-rshift-2.c (revision 0)
> +++ testsuite/gcc.dg/fold-and-rshift-2.c (working copy)
> @@ -0,0 +1,25 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-original" } */
> +
> +unsigned f(unsigned x)
> +{
> + return (x >> 29) & 32;
> +}
> +
> +unsigned g(unsigned x)
> +{
> + return !!(x & 0x80000000) << 5;
> +}
> +
> +unsigned j(unsigned x)
> +{
> + return ((x >> 31) & 1) ? 32 : 0;
> +}
> +
> +unsigned k(unsigned x)
> +{
> + return (x & 0x80000000) ? 32 : 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-not " \\? " "original" } } */
> +/* { dg-final { scan-assembler-not "sall" { target i?86-*-* x86_64-*-* } }
> }" */
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
