[clang] [llvm] [AMDGPU] Change CF intrinsics lowering to reconverge on predecessors (PR #108596)

[via cfe-commits]

================
@@ -446,8 +474,10 @@ define amdgpu_kernel void @add_i32_uniform(ptr addrspace(1) %out, ptr addrspace(
 ; GFX11W64-NEXT:    ; implicit-def: $vgpr1
 ; GFX11W64-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(NEXT) | instid1(VALU_DEP_1)
 ; GFX11W64-NEXT:    v_mbcnt_hi_u32_b32 v0, s5, v0
-; GFX11W64-NEXT:    v_cmpx_eq_u32_e32 0, v0
-; GFX11W64-NEXT:    s_cbranch_execz .LBB1_2
+; GFX11W64-NEXT:    v_cmp_eq_u32_e32 vcc, 0, v0
+; GFX11W64-NEXT:    s_cmp_lg_u64 vcc, 0
+; GFX11W64-NEXT:    s_cmov_b64 exec, vcc
+; GFX11W64-NEXT:    s_cbranch_scc0 .LBB1_2
----------------
ruiling wrote:

We can merge the s_cmp_lg for updating SCC and the exec save into one s_and_saveexec
```
s_and_saveexec_b64 s[0:1], vcc
s_cselect_b64 exec, vcc, s[0:1]
s_cbranch_scc0 .LBB1_2
```
so we don't need the separate `s_mov_b64 s[0:1], exec` at line 472 to save the exec.

https://github.com/llvm/llvm-project/pull/108596