Re: [Qemu-devel] [PULL 03/13] target-ppc: Use 32-bit rotate instead of deposit + 64-bit rotate

[Richard Henderson <rth@twiddle.net>]

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On 06/15/2016 10:19 PM, David Gibson wrote:
> On Wed, Jun 15, 2016 at 10:17:19PM +1000, Anton Blanchard wrote:
>> Hi,
>>
>>> From: Richard Henderson <rth@twiddle.net>
>>>
>>> A 32-bit rotate insn is more common on hosts than a deposit insn,
>>> and if the host has neither the result is truely horrific.
>>>
>>> At the same time, tidy up the temporaries within these functions,
>>> drop the over-use of "likely", drop some checks for identity that
>>> will also be checked by tcg-op.c functions, and special case mask
>>> without rotate within rlwinm.
>>
>> This breaks masks that wrap:
>>
>>         li      r3,-1
>>         li      r4,-1
>>         rlwnm   r3,r3,r4,22,8
>>
>> We expect:
>>
>> ffffffffff8003ff
>>
>> But get:
>>
>> ff8003ff
>>
>> Anton
> 
> Bother.  I've tentatively put a revert into ppc-for-2.7.  Richard, do
> you have a better idea how to fix it?

Please try the following.


r~




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>From f6059bc0e1303d898be2132a444bd58478a0eba0 Mon Sep 17 00:00:00 2001
From: Richard Henderson <rth@twiddle.net>
Date: Thu, 16 Jun 2016 19:00:12 +0000
Subject: [PATCH] target-ppc: Fix rlwimi, rlwinm, rlwnm

In 63ae0915f8ec, I arranged to use a 32-bit rotate, without
considering the effect of a mask value that wraps around to
the high bits of the word.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 target-ppc/translate.c | 73 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 52 insertions(+), 21 deletions(-)

diff --git a/target-ppc/translate.c b/target-ppc/translate.c
index b689475..12cfa37 100644
--- a/target-ppc/translate.c
+++ b/target-ppc/translate.c
@@ -1636,7 +1636,6 @@ static void gen_rlwimi(DisasContext *ctx)
         tcg_gen_deposit_tl(t_ra, t_ra, t_rs, sh, me - mb + 1);
     } else {
         target_ulong mask;
-        TCGv_i32 t0;
         TCGv t1;
 
 #if defined(TARGET_PPC64)
@@ -1645,12 +1644,21 @@ static void gen_rlwimi(DisasContext *ctx)
 #endif
         mask = MASK(mb, me);
 
-        t0 = tcg_temp_new_i32();
         t1 = tcg_temp_new();
-        tcg_gen_trunc_tl_i32(t0, t_rs);
-        tcg_gen_rotli_i32(t0, t0, sh);
-        tcg_gen_extu_i32_tl(t1, t0);
-        tcg_temp_free_i32(t0);
+        if (mask <= 0xffffffffu) {
+            TCGv_i32 t0 = tcg_temp_new_i32();
+            tcg_gen_trunc_tl_i32(t0, t_rs);
+            tcg_gen_rotli_i32(t0, t0, sh);
+            tcg_gen_extu_i32_tl(t1, t0);
+            tcg_temp_free_i32(t0);
+        } else {
+#if defined(TARGET_PPC64)
+            tcg_gen_deposit_i64(t1, t_rs, t_rs, 32, 32);
+            tcg_gen_rotli_i64(t1, t1, sh);
+#else
+            g_assert_not_reached();
+#endif
+        }
 
         tcg_gen_andi_tl(t1, t1, mask);
         tcg_gen_andi_tl(t_ra, t_ra, ~mask);
@@ -1678,20 +1686,30 @@ static void gen_rlwinm(DisasContext *ctx)
         tcg_gen_ext32u_tl(t_ra, t_rs);
         tcg_gen_shri_tl(t_ra, t_ra, mb);
     } else {
+        target_ulong mask;
 #if defined(TARGET_PPC64)
         mb += 32;
         me += 32;
 #endif
+        mask = MASK(mb, me);
+
         if (sh == 0) {
-            tcg_gen_andi_tl(t_ra, t_rs, MASK(mb, me));
-        } else {
+            tcg_gen_andi_tl(t_ra, t_rs, mask);
+        } else if (mask <= 0xffffffffu) {
             TCGv_i32 t0 = tcg_temp_new_i32();
-
             tcg_gen_trunc_tl_i32(t0, t_rs);
             tcg_gen_rotli_i32(t0, t0, sh);
-            tcg_gen_andi_i32(t0, t0, MASK(mb, me));
+            tcg_gen_andi_i32(t0, t0, mask);
             tcg_gen_extu_i32_tl(t_ra, t0);
             tcg_temp_free_i32(t0);
+        } else {
+#if defined(TARGET_PPC64)
+            tcg_gen_deposit_i64(t_ra, t_rs, t_rs, 32, 32);
+            tcg_gen_rotli_i64(t_ra, t_ra, sh);
+            tcg_gen_andi_i64(t_ra, t_ra, mask);
+#else
+            g_assert_not_reached();
+#endif
         }
     }
     if (unlikely(Rc(ctx->opcode) != 0)) {
@@ -1707,24 +1725,37 @@ static void gen_rlwnm(DisasContext *ctx)
     TCGv t_rb = cpu_gpr[rB(ctx->opcode)];
     uint32_t mb = MB(ctx->opcode);
     uint32_t me = ME(ctx->opcode);
-    TCGv_i32 t0, t1;
+    target_ulong mask;
 
 #if defined(TARGET_PPC64)
     mb += 32;
     me += 32;
 #endif
+    mask = MASK(mb, me);
 
-    t0 = tcg_temp_new_i32();
-    t1 = tcg_temp_new_i32();
-    tcg_gen_trunc_tl_i32(t0, t_rb);
-    tcg_gen_trunc_tl_i32(t1, t_rs);
-    tcg_gen_andi_i32(t0, t0, 0x1f);
-    tcg_gen_rotl_i32(t1, t1, t0);
-    tcg_temp_free_i32(t0);
+    if (mask <= 0xffffffffu) {
+        TCGv_i32 t0 = tcg_temp_new_i32();
+        TCGv_i32 t1 = tcg_temp_new_i32();
+        tcg_gen_trunc_tl_i32(t0, t_rb);
+        tcg_gen_trunc_tl_i32(t1, t_rs);
+        tcg_gen_andi_i32(t0, t0, 0x1f);
+        tcg_gen_rotl_i32(t1, t1, t0);
+        tcg_gen_extu_i32_tl(t_ra, t1);
+        tcg_temp_free_i32(t0);
+        tcg_temp_free_i32(t1);
+    } else {
+#if defined(TARGET_PPC64)
+        TCGv_i64 t0 = tcg_temp_new_i64();
+        tcg_gen_andi_i64(t0, t_rb, 0x1f);
+        tcg_gen_deposit_i64(t_ra, t_rs, t_rs, 32, 32);
+        tcg_gen_rotl_i64(t_ra, t_ra, t0);
+        tcg_temp_free_i64(t0);
+#else
+        g_assert_not_reached();
+#endif
+    }
 
-    tcg_gen_andi_i32(t1, t1, MASK(mb, me));
-    tcg_gen_extu_i32_tl(t_ra, t1);
-    tcg_temp_free_i32(t1);
+    tcg_gen_andi_tl(t_ra, t_ra, mask);
 
     if (unlikely(Rc(ctx->opcode) != 0)) {
         gen_set_Rc0(ctx, t_ra);
-- 
2.5.5