| Message ID | 20250129131127.1368879-1-pbonzini@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] tcg/optimize: optimize TSTNE using smask and zmask | expand |
On 1/29/25 05:11, Paolo Bonzini wrote: > Generalize the existing optimization of "TSTNE x,sign" and "TSTNE x,-1". > This can be useful for example in the i386 frontend, which will generate > tests of zero-extended registers against 0xffffffff. > > Ironically, on x86 hosts this is a very slight pessimization in the very > case it's meant to optimize because > > brcond_i64 cc_dst,$0xffffffff,tsteq,$L1 > > (test %ebx, %ebx) is 1 byte smaller than > > brcond_i64 cc_dst,$0x0,eq,$L1 > > (test %rbx, %rbx). However, in general it is an improvement, especially > if it avoids placing a large immediate in the constant pool. > > Signed-off-by: Paolo Bonzini<pbonzini@redhat.com> > --- > v2->v3: adjust for recent change to s_mask format > > tcg/optimize.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) Reviewed-by: Richard Henderson <richard.henderson@linaro.org> r~
diff --git a/tcg/optimize.c b/tcg/optimize.c index c23f0d13929..0f34b7d6068 100644 --- a/tcg/optimize.c +++ b/tcg/optimize.c @@ -765,6 +765,7 @@ static int do_constant_folding_cond1(OptContext *ctx, TCGOp *op, TCGArg dest, TCGArg *p1, TCGArg *p2, TCGArg *pcond) { TCGCond cond; + TempOptInfo *i1; bool swap; int r; @@ -782,19 +783,21 @@ static int do_constant_folding_cond1(OptContext *ctx, TCGOp *op, TCGArg dest, return -1; } + i1 = arg_info(*p1); + /* * TSTNE x,x -> NE x,0 - * TSTNE x,-1 -> NE x,0 + * TSTNE x,i -> NE x,0 if i includes all nonzero bits of x */ - if (args_are_copies(*p1, *p2) || arg_is_const_val(*p2, -1)) { + if (args_are_copies(*p1, *p2) || + (arg_is_const(*p2) && (i1->z_mask & ~arg_info(*p2)->val) == 0)) { *p2 = arg_new_constant(ctx, 0); *pcond = tcg_tst_eqne_cond(cond); return -1; } - /* TSTNE x,sign -> LT x,0 */ - if (arg_is_const_val(*p2, (ctx->type == TCG_TYPE_I32 - ? INT32_MIN : INT64_MIN))) { + /* TSTNE x,i -> LT x,0 if i only includes sign bit copies */ + if (arg_is_const(*p2) && (arg_info(*p2)->val & ~i1->s_mask) == 0) { *p2 = arg_new_constant(ctx, 0); *pcond = tcg_tst_ltge_cond(cond); return -1;
Generalize the existing optimization of "TSTNE x,sign" and "TSTNE x,-1". This can be useful for example in the i386 frontend, which will generate tests of zero-extended registers against 0xffffffff. Ironically, on x86 hosts this is a very slight pessimization in the very case it's meant to optimize because brcond_i64 cc_dst,$0xffffffff,tsteq,$L1 (test %ebx, %ebx) is 1 byte smaller than brcond_i64 cc_dst,$0x0,eq,$L1 (test %rbx, %rbx). However, in general it is an improvement, especially if it avoids placing a large immediate in the constant pool. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- v2->v3: adjust for recent change to s_mask format tcg/optimize.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-)