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

[Song, Ruiling]

Really strange corner case, I thought that normally the basic blocks have been sorted!
The patch looks good to me.

-----Original Message-----
From: beignet-bounces at lists.freedesktop.org [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of Zhigang Gong
Sent: Tuesday, December 17, 2013 1:26 PM
To: beignet at lists.freedesktop.org
Cc: Gong, Zhigang
Subject: [Beignet] [PATCH 2/2] GBE: fix a corner case which refer to a undefined value.

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

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