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Re: [Qemu-devel] [PATCH 4/7] tcg/mips: Support r6 JR encoding


From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH 4/7] tcg/mips: Support r6 JR encoding
Date: Thu, 1 Oct 2015 06:49:11 +1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0

On 10/01/2015 01:30 AM, James Hogan wrote:
MIPSr6 encodes JR as JALR with zero as the link register, and the pre-r6
JR encoding is removed. Update TCG to use the new encoding when built
for r6.

We still use the old encoding for pre-r6, so as not to confuse return
prediction stack hardware which may detect only particular encodings of
the return instruction.

Signed-off-by: James Hogan <address@hidden>
Cc: Richard Henderson <address@hidden>
Cc: Aurelien Jarno <address@hidden>
---
  tcg/mips/tcg-target.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tcg/mips/tcg-target.c b/tcg/mips/tcg-target.c
index 4305af967326..0a16140b1cdb 100644
--- a/tcg/mips/tcg-target.c
+++ b/tcg/mips/tcg-target.c
@@ -288,7 +288,7 @@ typedef enum {
      OPC_SRLV     = OPC_SPECIAL | 0x06,
      OPC_ROTRV    = OPC_SPECIAL | (0x01 <<  6) | 0x06,
      OPC_SRAV     = OPC_SPECIAL | 0x07,
-    OPC_JR       = OPC_SPECIAL | 0x08,
+    OPC_JR_R5    = OPC_SPECIAL | 0x08,
      OPC_JALR     = OPC_SPECIAL | 0x09,
      OPC_MOVZ     = OPC_SPECIAL | 0x0A,
      OPC_MOVN     = OPC_SPECIAL | 0x0B,
@@ -322,6 +322,9 @@ typedef enum {
      OPC_SEH      = OPC_SPECIAL3 | 0x620,
  } MIPSInsn;

+/* MIPS r6 doesn't have JR, JALR should be used instead */
+#define OPC_JR (use_mips32r6_instructions ? OPC_JALR : OPC_JR_R5)

This could be done in the enum instead of a define, but otherwise,


Reviewed-by: Richard Henderson <address@hidden>


r~





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