From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Fri, 10 Jul 2020 13:12:50 +0000 (+0100)
Subject: add test7 div regression
X-Git-Tag: div_pipeline~110
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=7c7e005ee8ca4d3f008573fded47a3a74a86739b;p=soc.git

add test7 div regression
---

diff --git a/src/soc/fu/div/output_stage.py b/src/soc/fu/div/output_stage.py
index 80968ea5..6b5a42ec 100644
--- a/src/soc/fu/div/output_stage.py
+++ b/src/soc/fu/div/output_stage.py
@@ -23,7 +23,7 @@ class DivOutputStage(PipeModBase):
         self.fields.create_specs()
         self.quotient_neg = Signal()
         self.remainder_neg = Signal()
-        self.quotient_64 = Signal(64)
+        self.quotient_65 = Signal(65) # one extra spare bit for overflow
         self.remainder_64 = Signal(64)
 
     def ispec(self):
@@ -48,7 +48,7 @@ class DivOutputStage(PipeModBase):
         abs_remainder = self.i.core.remainder[rem_start:rem_start+64]
         dividend_neg = self.i.dividend_neg
         divisor_neg = self.i.divisor_neg
-        quotient_64 = self.quotient_64
+        quotient_65 = self.quotient_65
         remainder_64 = self.remainder_64
 
         # work out if sign of result is to be negative
@@ -61,7 +61,7 @@ class DivOutputStage(PipeModBase):
         # result as negation of just the lower 32-bits, so we don't
         # need to do anything special before negating
         comb += [
-            quotient_64.eq(Mux(self.quotient_neg,
+            quotient_65.eq(Mux(self.quotient_neg,
                                -abs_quotient, abs_quotient)),
             remainder_64.eq(Mux(self.remainder_neg,
                                 -abs_remainder, abs_remainder))
@@ -92,6 +92,22 @@ class DivOutputStage(PipeModBase):
         with m.Else():
             calc_overflow(self.i.dive_abs_ov64, 0x8000000000000000)
 
+        # microwatt overflow detection
+        ov = Signal(reset_less=True)
+        with m.If(self.i.div_by_zero):
+            comb += ov.eq(1)
+        with m.Elif(~op.is_32bit):
+            comb += ov.eq(self.i.dive_abs_ov64)
+            with m.If(op.is_signed & (quotient_65[64] ^ quotient_65[63])):
+                comb += ov.eq(1)
+        with m.Elif(op.is_signed):
+            comb += ov.eq(self.i.dive_abs_ov32)
+            with m.If(quotient_65[32] != quotient_65[31]):
+                comb += ov.eq(1)
+        with m.Else():
+            comb += ov.eq(self.i.dive_abs_ov32)
+        comb += xer_ov.eq(Repl(ov, 2)) # set OV _and_ OV32
+
         ##########################
         # main switch for DIV
 
@@ -102,20 +118,20 @@ class DivOutputStage(PipeModBase):
                 with m.If(op.is_32bit):
                     with m.If(op.is_signed):
                         # matches POWER9's divweo behavior
-                        comb += o.eq(quotient_64[0:32].as_unsigned())
+                        comb += o.eq(quotient_65[0:32].as_unsigned())
                     with m.Else():
-                        comb += o.eq(quotient_64[0:32].as_unsigned())
+                        comb += o.eq(quotient_65[0:32].as_unsigned())
                 with m.Else():
-                    comb += o.eq(quotient_64)
+                    comb += o.eq(quotient_65)
             with m.Case(InternalOp.OP_DIV):
                 with m.If(op.is_32bit):
                     with m.If(op.is_signed):
                         # matches POWER9's divwo behavior
-                        comb += o.eq(quotient_64[0:32].as_unsigned())
+                        comb += o.eq(quotient_65[0:32].as_unsigned())
                     with m.Else():
-                        comb += o.eq(quotient_64[0:32].as_unsigned())
+                        comb += o.eq(quotient_65[0:32].as_unsigned())
                 with m.Else():
-                    comb += o.eq(quotient_64)
+                    comb += o.eq(quotient_65)
             with m.Case(InternalOp.OP_MOD):
                 with m.If(op.is_32bit):
                     with m.If(op.is_signed):
diff --git a/src/soc/fu/div/test/test_pipe_caller.py b/src/soc/fu/div/test/test_pipe_caller.py
index 9525a337..663bb0ac 100644
--- a/src/soc/fu/div/test/test_pipe_caller.py
+++ b/src/soc/fu/div/test/test_pipe_caller.py
@@ -132,6 +132,14 @@ class DIVTestCase(FHDLTestCase):
         initial_regs[2] = 0x9dc66a7622c32bc0
         self.run_tst_program(Program(lst), initial_regs)
 
+    def test_7_regression(self):
+        # https://bugs.libre-soc.org/show_bug.cgi?id=425
+        lst = ["divw. 3, 1, 2"]
+        initial_regs = [0] * 32
+        initial_regs[1] = 0xf1791627e05e8096
+        initial_regs[2] = 0xffc868bf4573da0b
+        self.run_tst_program(Program(lst), initial_regs)
+
     def tst_rand_divw(self):
         insns = ["divw", "divw.", "divwo", "divwo."]
         for i in range(40):
@@ -223,12 +231,14 @@ class TestRunner(FHDLTestCase):
                         is_32bit = yield ctx_op.is_32bit
                         is_signed = yield ctx_op.is_signed
                         quotient_root = yield do.i.core.quotient_root
+                        quotient_65 = yield do.quotient_65
                         dive_abs_ov32 = yield do.i.dive_abs_ov32
                         div_by_zero = yield do.i.div_by_zero
                         quotient_neg = yield do.quotient_neg
                         print ("32bit", hex(is_32bit))
                         print ("signed", hex(is_signed))
                         print ("quotient_root", hex(quotient_root))
+                        print ("quotient_65", hex(quotient_65))
                         print ("div_by_zero", hex(div_by_zero))
                         print ("dive_abs_ov32", hex(dive_abs_ov32))
                         print ("quotient_neg", hex(quotient_neg))