[Beignet] [PATCH 2/2] GBE: fix a corner case which refer to a undefined value.

[Zhigang Gong]

Clang/llvm may generate some code similar to the following IRs:

... (there is no definition of %7)
  br label 2

label1:
  %10 = add  %7, %6
  ...
  ret

label2:
  %7 = ...
  br label1

The value %7 is assigned after label2 but is referred at label1.
>From the control flow, the IRs is valid. As the reference will
be executed after the assignment.

But our current virtual register allocation assume that all the
values are assigned before any usage from the instructions' order
view which is incorrect for this case.

This patch choose a simple way to fix this issue. It allocate
register when it fails to get one. And latter when emit the assignment
instruction, it just ignore the duplicate allocation.

Signed-off-by: Zhigang Gong <zhigang.gong at intel.com>
---
 backend/src/llvm/llvm_gen_backend.cpp |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/backend/src/llvm/llvm_gen_backend.cpp b/backend/src/llvm/llvm_gen_backend.cpp
index 5755ac4..2654eba 100644
--- a/backend/src/llvm/llvm_gen_backend.cpp
+++ b/backend/src/llvm/llvm_gen_backend.cpp
@@ -407,8 +407,10 @@ namespace gbe
      */
     ir::Register newScalar(Value *value, Value *key, Type *type, uint32_t index) {
       const ir::RegisterFamily family = getFamily(ctx, type);
-      const ir::Register reg = ctx.reg(family);
       key = key == NULL ? value : key;
+      if (scalarMap.find(std::make_pair(key, index)) != scalarMap.end())
+        return scalarMap[std::make_pair(key, index)];
+      const ir::Register reg = ctx.reg(family);
       this->insertRegister(reg, key, index);
       return reg;
     }
@@ -971,8 +973,11 @@ namespace gbe
     if(isa<Constant>(value)) {
       Constant *c = dyn_cast<Constant>(value);
       return getConstantRegister(c, elemID);
-    } else
+    } else {
+      if (!(regTranslator.valueExists(value, elemID)))
+        this->newRegister(value);
       return regTranslator.getScalar(value, elemID);
+    }
   }
 
   INLINE Value *GenWriter::getPHICopy(Value *PHI) {
-- 
1.7.9.5