From: Sandipan Das <sandipan@linux.ibm.com>
Date: Sat, 6 Feb 2021 11:51:00 +0000 (+0530)
Subject: arch-power: Add character compare instructions
X-Git-Tag: develop-gem5-snapshot~36
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=22535322445c80df4f8c0979200a2d1211fd5edc;p=gem5.git

arch-power: Add character compare instructions

This adds the following instructions.
  * Compare Ranged Byte (cmprb)
  * Compare Equal Byte (cmpeqb)

Change-Id: I12a9135bf302acd741abe27cb557e8e8bba82edc
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
---

diff --git a/src/arch/power/isa/decoder.isa b/src/arch/power/isa/decoder.isa
index 63d3afc14..d5b2a341b 100644
--- a/src/arch/power/isa/decoder.isa
+++ b/src/arch/power/isa/decoder.isa
@@ -458,6 +458,30 @@ decode PO default Unknown::unknown() {
                     cr = makeCRField((uint32_t)Ra, (uint32_t)Rb, xer.so);
                 }
             }});
+
+            192: cmprb({{
+                uint32_t src1 = Ra_ub;
+                uint32_t src2 = Rb_uw;
+                uint8_t src2lo = src2 & 0xff;
+                uint8_t src2hi = (src2 >>= 8) & 0xff;
+                uint32_t res = (src2lo <= src1) & (src1 <= src2hi);
+                if (length) {
+                    src2lo = (src2 >>= 8) & 0xff;
+                    src2hi = (src2 >>= 8) & 0xff;
+                    res = ((src2lo <= src1) & (src1 <= src2hi)) | res;
+                }
+                cr = res << 2;
+            }});
+
+            224: cmpeqb({{
+                // Based on "Determine if a word has a byte equal to n"
+                // from https://graphics.stanford.edu/~seander/bithacks.html
+                const uint64_t m1 = 0x0101010101010101;
+                const uint64_t m2 = 0x8080808080808080;
+                uint64_t res = Rb ^ (Ra_ub * m1);
+                res = (res - m1) & ~res & m2;
+                cr = (res != 0) << 2;
+            }});
         }
 
         // Integer logic instructions use source registers Rs and Rb,
diff --git a/src/arch/power/isa/formats/integer.isa b/src/arch/power/isa/formats/integer.isa
index 9a3e0d8fd..87763698b 100644
--- a/src/arch/power/isa/formats/integer.isa
+++ b/src/arch/power/isa/formats/integer.isa
@@ -71,7 +71,7 @@ def template IntRcOeConstructor {{
 
 let {{
 
-readXERCode = 'Xer xer = XER;'
+readXERCode = 'M5_VAR_USED Xer xer = XER;'
 
 setXERCode = 'XER = xer;'