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[PULL,09/21] target/arm: Fix SMMLS argument order

Message ID 20190903153633.6651-10-peter.maydell@linaro.org
State Accepted
Commit e0a0c8322b8ebcdad674f443a3e86db8708d6738
Headers show
Series target-arm queue | expand

Commit Message

Peter Maydell Sept. 3, 2019, 3:36 p.m. UTC 
From: Richard Henderson <richard.henderson@linaro.org>


The previous simplification got the order of operands to the
subtraction wrong.  Since the 64-bit product is the subtrahend,
we must use a 64-bit subtract to properly compute the borrow
from the low-part of the product.

Fixes: 5f8cd06ebcf5 ("target/arm: Simplify SMMLA, SMMLAR, SMMLS, SMMLSR")
Reported-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Tested-by: Laurent Desnogues <laurent.desnogues@gmail.com>

Message-id: 20190829013258.16102-1-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

---
 target/arm/translate.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

-- 
2.20.1
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Patch

diff --git a/target/arm/translate.c b/target/arm/translate.c
index 78d93f63cab..cfebd35d268 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -8831,7 +8831,16 @@  static void disas_arm_insn(DisasContext *s, unsigned int insn)
                         if (rd != 15) {
                             tmp3 = load_reg(s, rd);
                             if (insn & (1 << 6)) {
-                                tcg_gen_sub_i32(tmp, tmp, tmp3);
+                                /*
+                                 * For SMMLS, we need a 64-bit subtract.
+                                 * Borrow caused by a non-zero multiplicand
+                                 * lowpart, and the correct result lowpart
+                                 * for rounding.
+                                 */
+                                TCGv_i32 zero = tcg_const_i32(0);
+                                tcg_gen_sub2_i32(tmp2, tmp, zero, tmp3,
+                                                 tmp2, tmp);
+                                tcg_temp_free_i32(zero);
                             } else {
                                 tcg_gen_add_i32(tmp, tmp, tmp3);
                             }
@@ -10075,7 +10084,14 @@  static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
                     if (insn & (1 << 20)) {
                         tcg_gen_add_i32(tmp, tmp, tmp3);
                     } else {
-                        tcg_gen_sub_i32(tmp, tmp, tmp3);
+                        /*
+                         * For SMMLS, we need a 64-bit subtract.
+                         * Borrow caused by a non-zero multiplicand lowpart,
+                         * and the correct result lowpart for rounding.
+                         */
+                        TCGv_i32 zero = tcg_const_i32(0);
+                        tcg_gen_sub2_i32(tmp2, tmp, zero, tmp3, tmp2, tmp);
+                        tcg_temp_free_i32(zero);
                     }
                     tcg_temp_free_i32(tmp3);
                 }