[Beignet] [PATCH] GBE: fix a bool handling bug when SEL on a uniform bool variable.

[Zhigang Gong]

If a SEL uses a bool variable which is a uniform bool, even
we can get a dag node within the same BB, we still need to
set the externFlag bit. The reason is that we don't know how
to generate a scalar physical flag.

Signed-off-by: Zhigang Gong <zhigang.gong at intel.com>
---
 backend/src/backend/gen_insn_selection.cpp | 11 ++++++++++-
 backend/src/backend/gen_reg_allocation.cpp |  2 ++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/backend/src/backend/gen_insn_selection.cpp b/backend/src/backend/gen_insn_selection.cpp
index 64e9fd8..bd19702 100644
--- a/backend/src/backend/gen_insn_selection.cpp
+++ b/backend/src/backend/gen_insn_selection.cpp
@@ -3804,7 +3804,16 @@ namespace gbe
         sel.curr.physicalFlag = 0;
         sel.curr.flagIndex = (uint16_t) pred;
         sel.curr.predicate = GEN_PREDICATE_NORMAL;
-        if (!dag0)
+        // FIXME in general, if the flag is a uniform flag.
+        // we should treat that flag as extern flag, as we
+        // never genrate a uniform physical flag. As we can
+        // never predicate which channel is active when this
+        // flag is used.
+        // We need to concentrate this logic to the modFlag bit.
+        // If an instruction has that bit, it will generate physical
+        // flag, otherwise it will not. But current modFlag is
+        // just a hint. We need to fix it in the future.
+        if (!dag0 || (sel.isScalarReg(dag0->insn.getDst(0))))
           sel.curr.externFlag = 1;
         if(type == ir::TYPE_S64 || type == ir::TYPE_U64)
           sel.SEL_INT64(dst, src0, src1);
diff --git a/backend/src/backend/gen_reg_allocation.cpp b/backend/src/backend/gen_reg_allocation.cpp
index ef519d9..18f60ca 100644
--- a/backend/src/backend/gen_reg_allocation.cpp
+++ b/backend/src/backend/gen_reg_allocation.cpp
@@ -585,6 +585,8 @@ namespace gbe
               // If this is a modFlag on a scalar bool, we need to remove it
               // from the allocated flags map. Then latter, the user could
               // validate the flag from the scalar value correctly.
+              // The reason is we can not predicate the active channel when we
+              // need to use this flag.
               if (IS_SCALAR_FLAG(insn)) {
                 allocatedFlags.erase(ir::Register(insn.state.flagIndex));
                 continue;
-- 
1.8.3.2