[AMDGPU] Fixed hang during DAG combine

SITargetLowering::reassociateScalarOps() does not touch constants
so that DAGCombiner::ReassociateOps() does not revert the combine.
However a global address is not a ConstantSDNode.

Switched to the method used by DAGCombiner::ReassociateOps() itself
to detect constants.

Differential Revision: https://reviews.llvm.org/D58695

llvm-svn: 354926

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -8477,7 +8477,8 @@ SDValue SITargetLowering::reassociateScalarOps(SDNode *N,
 
   // If either operand is constant this will conflict with
   // DAGCombiner::ReassociateOps().
-  if (isa<ConstantSDNode>(Op0) || isa<ConstantSDNode>(Op1))
+  if (DAG.isConstantIntBuildVectorOrConstantInt(Op0) ||
+      DAG.isConstantIntBuildVectorOrConstantInt(Op1))
     return SDValue();
 
   SDLoc SL(N);

llvm/test/CodeGen/AMDGPU/reassoc-scalar.ll

@@ -109,5 +109,21 @@ bb:
   ret void
 }
 
+@var = common hidden local_unnamed_addr addrspace(1) global [4 x i32] zeroinitializer, align 4
+
+; GCN-LABEL: reassoc_i32_ga:
+; GCN: s_add_u32 s{{[0-9]+}}, s{{[0-9]+}}, var@rel32@lo+4
+; GCN: s_addc_u32 s{{[0-9]+}}, s{{[0-9]+}}, var@rel32@hi+4
+; GCN: s_endpgm
+define amdgpu_kernel void @reassoc_i32_ga(i64 %x) {
+bb:
+  %tid = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %t64 = zext i32 %tid to i64
+  %add1 = getelementptr [4 x i32], [4 x i32] addrspace(1)* @var, i64 0, i64 %t64
+  %add2 = getelementptr i32, i32 addrspace(1)* %add1, i64 %x
+  store volatile i32 1, i32 addrspace(1)* %add2, align 4
+  ret void
+}
+
 declare i32 @llvm.amdgcn.workitem.id.x()
 declare i32 @llvm.amdgcn.workitem.id.y()