[llvm] [GlobalIsel] Combine G_ADD and G_SUB (PR #92879)

[Thorsten Schütt via llvm-commits]

================
@@ -1634,6 +1634,78 @@ extract_vector_element_shuffle_vector,
 insert_vector_element_extract_vector_element
 ]>;
 
+
+// fold ((0-A) + B) -> B-A
+def ZeroMinusAPlusB : GICombineRule<
+   (defs root:$root),
+   (match (G_SUB $sub, 0, $A),
+          (G_ADD $root, $sub, $B)),
+   (apply (G_SUB $root, $B, $A))>;
+
+// fold (A + (0-B)) -> A-B
+def APlusZeroMinusB : GICombineRule<
+   (defs root:$root),
+   (match (G_SUB $sub, 0, $B),
+          (G_ADD $root, $A, $sub)),
+   (apply (G_SUB $root, $A, $B))>;
+
+ // fold (A+(B-A)) -> B
+ def APlusBMinusB : GICombineRule<
+   (defs root:$root),
+   (match (G_SUB $sub, $B, $A),
+          (G_ADD $root, $A, $sub)),
+   (apply (GIReplaceReg $root, $B))>;
+
+// fold ((B-A)+A) -> B
+ def BMinusAPlusA : GICombineRule<
+   (defs root:$root),
+   (match (G_SUB $sub, $B, $A),
+          (G_ADD $root, $sub, $A)),
+   (apply (GIReplaceReg $root, $B))>;
+
+// fold ((A-B)+(C-A)) -> (C-B)
+def AMinusBPlusCMinusA : GICombineRule<
+   (defs root:$root),
+   (match (G_SUB $sub1, $A, $B),
+          (G_SUB $sub2, $C, $A),
+          (G_ADD $root, $sub1, $sub2)),
+   (apply (G_SUB $root, $C, $B))>;
+
+// fold ((A-B)+(B-C)) -> (A-C)
+def AMinusBPlusBMinusC : GICombineRule<
+   (defs root:$root),
+   (match (G_SUB $sub1, $A, $B),
+          (G_SUB $sub2, $B, $C),
+          (G_ADD $root, $sub1, $sub2)),
+   (apply (G_SUB $root, $A, $C))>;
+
+// fold (A+(B-(A+C))) to (B-C)
+def APlusBMinusAplusC : GICombineRule<
+   (defs root:$root),
+   (match (G_ADD $add1, $A, $C),
+          (G_SUB $sub1, $B, $add1),
+          (G_ADD $root, $A, $sub1)),
+   (apply (G_SUB $root, $B, $C))>;
+
+// fold (A+(B-(C+A))) to (B-C)
+def APlusBMinusCPlusA : GICombineRule<
+   (defs root:$root),
+   (match (G_ADD $add1, $C, $A),
+          (G_SUB $sub1, $B, $add1),
+          (G_ADD $root, $A, $sub1)),
+   (apply (G_SUB $root, $B, $C))>;
+
+def integer_reassoc_combines: GICombineGroup<[
+ZeroMinusAPlusB,
----------------
tschuett wrote:

Could please elaborate? Indent by 2 spaces?

https://github.com/llvm/llvm-project/pull/92879