[llvm] [AMDGPU][DAGCombiner][GlobalISel] Prevent FMA contraction when multiply cannot be eliminated (PR #169735)

[Matt Arsenault via llvm-commits]

================
@@ -234,11 +234,11 @@ define float @test_powr_fast_f32(float %x, float %y) {
 ; CHECK-NEXT:    v_cndmask_b32_e32 v2, 0, v2, vcc
 ; CHECK-NEXT:    s_mov_b32 s4, 0xc2fc0000
 ; CHECK-NEXT:    v_sub_f32_e32 v0, v0, v2
-; CHECK-NEXT:    v_mul_f32_e32 v2, v1, v0
-; CHECK-NEXT:    v_mov_b32_e32 v3, 0x42800000
-; CHECK-NEXT:    v_cmp_gt_f32_e32 vcc, s4, v2
-; CHECK-NEXT:    v_cndmask_b32_e32 v2, 0, v3, vcc
-; CHECK-NEXT:    v_fma_f32 v0, v1, v0, v2
+; CHECK-NEXT:    v_mul_f32_e32 v0, v1, v0
+; CHECK-NEXT:    v_mov_b32_e32 v1, 0x42800000
+; CHECK-NEXT:    v_cmp_gt_f32_e32 vcc, s4, v0
+; CHECK-NEXT:    v_cndmask_b32_e32 v1, 0, v1, vcc
+; CHECK-NEXT:    v_add_f32_e32 v0, v0, v1
----------------
arsenm wrote:

This is possibly better 

https://github.com/llvm/llvm-project/pull/169735