From: Richard Henderson <[email protected]> Skip s_mask computation for logical right shift.
Cc: [email protected] Fixes: 93a967fbb57 ("tcg/optimize: Propagate sign info for shifting") Reported-by: Jacob Young <[email protected]> Signed-off-by: Richard Henderson <[email protected]> (cherry picked from commit 5fe51606146cbf04dac07bf27256febbe56881e7) (Mjt: back-port to 10.0 across v10.0.0-1791-g03329e3ce460 "tcg/optimize: Build and use o_bits in fold_shift" and v10.0.0-425-g74dbd36f1f87 "tcg: Merge INDEX_op_shr_{i32,i64}") Signed-off-by: Michael Tokarev <[email protected]> diff --git a/tcg/optimize.c b/tcg/optimize.c index 1b9553737e2..c7c16518f08 100644 --- a/tcg/optimize.c +++ b/tcg/optimize.c @@ -2602,8 +2602,17 @@ static bool fold_shift(OptContext *ctx, TCGOp *op) int sh = ti_const_val(t2); z_mask = do_constant_folding(op->opc, ctx->type, z_mask, sh); - s_mask = do_constant_folding(op->opc, ctx->type, s_mask, sh); + if (op->opc == INDEX_op_shr_i32 || op->opc == INDEX_op_shr_i64) { + /* + * Logical right shift will force the sign bit zero. + * Don't bother computing s_mask and let fold_masks + * recompute from z_mask. + */ + return fold_masks_z(ctx, op, z_mask); + } + + s_mask = do_constant_folding(op->opc, ctx->type, s_mask, sh); return fold_masks_zs(ctx, op, z_mask, s_mask); } diff --git a/tests/tcg/i386/test-i386-opt-shr.c b/tests/tcg/i386/test-i386-opt-shr.c new file mode 100644 index 00000000000..9fb8d420223 --- /dev/null +++ b/tests/tcg/i386/test-i386-opt-shr.c @@ -0,0 +1,21 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* Regression test for tcg optimize vs sign bit repetition counting. */ + +#include <assert.h> + +int main() +{ +#ifndef __x86_64__ + char test; + + asm("movw $0x4000, %%ax\n\t" + "addw %%ax, %%ax\n\t" + "cwtl\n\t" + "shrl %%eax\n\t" + "cmpw $-0x3fff, %%ax\n\t" + "setnl %%al" + : "=a"(test)); + assert(!test); +#endif + return 0; +} -- 2.47.3
