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tcg/arm: Simplify usage of encode_imm

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We have already computed the rotated value of the imm8
portion of the complete imm12 encoding.  No sense leaving
the combination of rot + rotation to the caller.

Create an encode_imm12_nofail helper that performs an assert.

This removes the final use of the local "rotl" function,
which duplicated our generic "rol32" function.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2021-08-09 12:27:08 -10:00
parent 31d160adc9
commit 90606715dc
1 changed files with 77 additions and 64 deletions
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141
tcg/arm/tcg-target.c.inc
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@ -312,10 +312,10 @@ static bool reloc_pc8(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
{
const tcg_insn_unit *src_rx = tcg_splitwx_to_rx(src_rw);
ptrdiff_t offset = tcg_ptr_byte_diff(target, src_rx) - 8;
int rot = encode_imm(offset);
int imm12 = encode_imm(offset);
if (rot >= 0) {
*src_rw = deposit32(*src_rw, 0, 12, rol32(offset, rot) | (rot << 7));
if (imm12 >= 0) {
*src_rw = deposit32(*src_rw, 0, 12, imm12);
return true;
}
return false;
@ -369,33 +369,52 @@ static bool patch_reloc(tcg_insn_unit *code_ptr, int type,
(ALL_GENERAL_REGS & ~((1 << TCG_REG_R0) | (1 << TCG_REG_R1)))
#endif
static inline uint32_t rotl(uint32_t val, int n)
{
return (val << n) | (val >> (32 - n));
}
/* ARM immediates for ALU instructions are made of an unsigned 8-bit
right-rotated by an even amount between 0 and 30. */
/*
* ARM immediates for ALU instructions are made of an unsigned 8-bit
* right-rotated by an even amount between 0 and 30.
*
* Return < 0 if @imm cannot be encoded, else the entire imm12 field.
*/
static int encode_imm(uint32_t imm)
{
int shift;
uint32_t rot, imm8;
/* simple case, only lower bits */
if ((imm & ~0xff) == 0)
return 0;
/* then try a simple even shift */
shift = ctz32(imm) & ~1;
if (((imm >> shift) & ~0xff) == 0)
return 32 - shift;
/* now try harder with rotations */
if ((rotl(imm, 2) & ~0xff) == 0)
return 2;
if ((rotl(imm, 4) & ~0xff) == 0)
return 4;
if ((rotl(imm, 6) & ~0xff) == 0)
return 6;
/* imm can't be encoded */
/* Simple case, no rotation required. */
if ((imm & ~0xff) == 0) {
return imm;
}
/* Next, try a simple even shift. */
rot = ctz32(imm) & ~1;
imm8 = imm >> rot;
rot = 32 - rot;
if ((imm8 & ~0xff) == 0) {
goto found;
}
/*
* Finally, try harder with rotations.
* The ctz test above will have taken care of rotates >= 8.
*/
for (rot = 2; rot < 8; rot += 2) {
imm8 = rol32(imm, rot);
if ((imm8 & ~0xff) == 0) {
goto found;
}
}
/* Fail: imm cannot be encoded. */
return -1;
found:
/* Note that rot is even, and we discard bit 0 by shifting by 7. */
return rot << 7 | imm8;
}
static int encode_imm_nofail(uint32_t imm)
{
int ret = encode_imm(imm);
tcg_debug_assert(ret >= 0);
return ret;
}
static inline int check_fit_imm(uint32_t imm)
@ -782,20 +801,18 @@ static void tcg_out_movi_pool(TCGContext *s, int cond, int rd, uint32_t arg)
static void tcg_out_movi32(TCGContext *s, int cond, int rd, uint32_t arg)
{
int rot, diff, opc, sh1, sh2;
int imm12, diff, opc, sh1, sh2;
uint32_t tt0, tt1, tt2;
/* Check a single MOV/MVN before anything else. */
rot = encode_imm(arg);
if (rot >= 0) {
tcg_out_dat_imm(s, cond, ARITH_MOV, rd, 0,
rotl(arg, rot) | (rot << 7));
imm12 = encode_imm(arg);
if (imm12 >= 0) {
tcg_out_dat_imm(s, cond, ARITH_MOV, rd, 0, imm12);
return;
}
rot = encode_imm(~arg);
if (rot >= 0) {
tcg_out_dat_imm(s, cond, ARITH_MVN, rd, 0,
rotl(~arg, rot) | (rot << 7));
imm12 = encode_imm(~arg);
if (imm12 >= 0) {
tcg_out_dat_imm(s, cond, ARITH_MVN, rd, 0, imm12);
return;
}
@ -803,17 +820,15 @@ static void tcg_out_movi32(TCGContext *s, int cond, int rd, uint32_t arg)
or within the TB, which is immediately before the code block. */
diff = tcg_pcrel_diff(s, (void *)arg) - 8;
if (diff >= 0) {
rot = encode_imm(diff);
if (rot >= 0) {
tcg_out_dat_imm(s, cond, ARITH_ADD, rd, TCG_REG_PC,
rotl(diff, rot) | (rot << 7));
imm12 = encode_imm(diff);
if (imm12 >= 0) {
tcg_out_dat_imm(s, cond, ARITH_ADD, rd, TCG_REG_PC, imm12);
return;
}
} else {
rot = encode_imm(-diff);
if (rot >= 0) {
tcg_out_dat_imm(s, cond, ARITH_SUB, rd, TCG_REG_PC,
rotl(-diff, rot) | (rot << 7));
imm12 = encode_imm(-diff);
if (imm12 >= 0) {
tcg_out_dat_imm(s, cond, ARITH_SUB, rd, TCG_REG_PC, imm12);
return;
}
}
@ -845,6 +860,8 @@ static void tcg_out_movi32(TCGContext *s, int cond, int rd, uint32_t arg)
sh2 = ctz32(tt1) & ~1;
tt2 = tt1 & ~(0xff << sh2);
if (tt2 == 0) {
int rot;
rot = ((32 - sh1) << 7) & 0xf00;
tcg_out_dat_imm(s, cond, opc, rd, 0, ((tt0 >> sh1) & 0xff) | rot);
rot = ((32 - sh2) << 7) & 0xf00;
@ -857,37 +874,35 @@ static void tcg_out_movi32(TCGContext *s, int cond, int rd, uint32_t arg)
tcg_out_movi_pool(s, cond, rd, arg);
}
/*
* Emit either the reg,imm or reg,reg form of a data-processing insn.
* rhs must satisfy the "rI" constraint.
*/
static inline void tcg_out_dat_rI(TCGContext *s, int cond, int opc, TCGArg dst,
TCGArg lhs, TCGArg rhs, int rhs_is_const)
{
/* Emit either the reg,imm or reg,reg form of a data-processing insn.
* rhs must satisfy the "rI" constraint.
*/
if (rhs_is_const) {
int rot = encode_imm(rhs);
tcg_debug_assert(rot >= 0);
tcg_out_dat_imm(s, cond, opc, dst, lhs, rotl(rhs, rot) | (rot << 7));
tcg_out_dat_imm(s, cond, opc, dst, lhs, encode_imm_nofail(rhs));
} else {
tcg_out_dat_reg(s, cond, opc, dst, lhs, rhs, SHIFT_IMM_LSL(0));
}
}
/*
* Emit either the reg,imm or reg,reg form of a data-processing insn.
* rhs must satisfy the "rIK" constraint.
*/
static void tcg_out_dat_rIK(TCGContext *s, int cond, int opc, int opinv,
TCGReg dst, TCGReg lhs, TCGArg rhs,
bool rhs_is_const)
{
/* Emit either the reg,imm or reg,reg form of a data-processing insn.
* rhs must satisfy the "rIK" constraint.
*/
if (rhs_is_const) {
int rot = encode_imm(rhs);
if (rot < 0) {
rhs = ~rhs;
rot = encode_imm(rhs);
tcg_debug_assert(rot >= 0);
int imm12 = encode_imm(rhs);
if (imm12 < 0) {
imm12 = encode_imm_nofail(~rhs);
opc = opinv;
}
tcg_out_dat_imm(s, cond, opc, dst, lhs, rotl(rhs, rot) | (rot << 7));
tcg_out_dat_imm(s, cond, opc, dst, lhs, imm12);
} else {
tcg_out_dat_reg(s, cond, opc, dst, lhs, rhs, SHIFT_IMM_LSL(0));
}
@ -901,14 +916,12 @@ static void tcg_out_dat_rIN(TCGContext *s, int cond, int opc, int opneg,
* rhs must satisfy the "rIN" constraint.
*/
if (rhs_is_const) {
int rot = encode_imm(rhs);
if (rot < 0) {
rhs = -rhs;
rot = encode_imm(rhs);
tcg_debug_assert(rot >= 0);
int imm12 = encode_imm(rhs);
if (imm12 < 0) {
imm12 = encode_imm_nofail(-rhs);
opc = opneg;
}
tcg_out_dat_imm(s, cond, opc, dst, lhs, rotl(rhs, rot) | (rot << 7));
tcg_out_dat_imm(s, cond, opc, dst, lhs, imm12);
} else {
tcg_out_dat_reg(s, cond, opc, dst, lhs, rhs, SHIFT_IMM_LSL(0));
}