[StructurizeCFG] Enable -structurizecfg-relaxed-uniform-regions by default

[tpr]

Summary

D62198 introduced an option to relax the checks for
hasOnlyUniformBranches. This commit turns the option on by default, for
better code generation in some cases in AMDGPU.

Change-Id: I9cbff002a1e74d3b7eb96b4192dc8129936d537d

[tpr]

V2: Lit test fix.

lib/Transforms/Scalar/StructurizeCFG.cpp

static cl::opt<bool> ForceSkipUniformRegions(
   "structurizecfg-skip-uniform-regions",
   cl::Hidden,
   cl::desc("Force whether the StructurizeCFG pass skips uniform regions"),
   cl::init(false));
 
 static cl::opt<bool>
     RelaxedUniformRegions("structurizecfg-relaxed-uniform-regions", cl::Hidden,
                           cl::desc("Allow relaxed uniform region checks"),
-                          cl::init(false));
+                          cl::init(true));
 
 // Definition of the complex types used in this pass.
 
 using BBValuePair = std::pair<BasicBlock *, Value *>;
 
 using RNVector = SmallVector<RegionNode *, 8>;
 using BBVector = SmallVector<BasicBlock *, 8>;
 using BranchVector = SmallVector<BranchInst *, 8>;

test/CodeGen/AMDGPU/control-flow-optnone.ll

 ; GCN: s_branch
 
 ; GCN-DAG: v_cmp_lt_i32
 ; GCN-DAG: v_cmp_gt_i32
 ; GCN: s_and_b64
 ; GCN: s_mov_b64 exec
 
 ; GCN: s_or_b64 exec, exec
-; GCN: v_cmp_eq_u32
-; GCN: s_cbranch_vccnz
+; GCN: s_cmp_eq_u32
+; GCN: s_cbranch_scc1
 ; GCN-NEXT: s_branch
 define amdgpu_kernel void @copytoreg_divergent_brcond(i32 %arg, i32 %arg1, i32 %arg2) #0 {
 bb:
   %tmp = tail call i32 @llvm.amdgcn.workitem.id.x()
   %tmp3 = zext i32 %tmp to i64
   %tmp5 = add i64 %tmp3, undef
   %tmp6 = trunc i64 %tmp5 to i32
   %tmp7 = mul nsw i32 %tmp6, %arg2