X86: Fix the sign extension microop so it extends zeros correctly.

--HG--
extra : convert_revision : 9d7ca286ba7709175fa75226320601acce4ced98

1 files changed, 4 insertions, 2 deletions

diff --git a/src/arch/x86/isa/microops/regop.isa b/src/arch/x86/isa/microops/regop.isa
index 608b86a70..b91c77c21 100644
--- a/src/arch/x86/isa/microops/regop.isa
+++ b/src/arch/x86/isa/microops/regop.isa
@@ -661,8 +661,10 @@ let {{
     defineMicroRegOpImm('Sext', '''
             IntReg val = psrc1;
             int sign_bit = bits(val, imm8-1, imm8-1);
-            val = sign_bit ? (val | ~mask(imm8)) : val;
-            DestReg = merge(DestReg, val, dataSize);''')
+            uint64_t maskVal = mask(imm8);
+            val = sign_bit ? (val | ~maskVal) : (val & maskVal);
+            DestReg = merge(DestReg, val, dataSize);
+            ''')
 
     defineMicroRegOpImm('Zext', 'DestReg = bits(psrc1, imm8-1, 0);')
 }};