[llvm] [RISCV] Expand mul to shNadd x, (slli x, c) in DAGCombine (PR #88524)

[Philip Reames via llvm-commits]

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@@ -551,8 +551,9 @@ define i64 @add_mul_combine_infinite_loop(i64 %x) {
 ; RV32IMB-NEXT:    sh3add a1, a1, a2
 ; RV32IMB-NEXT:    sh1add a0, a0, a0
 ; RV32IMB-NEXT:    slli a2, a0, 3
-; RV32IMB-NEXT:    addi a0, a2, 2047
-; RV32IMB-NEXT:    addi a0, a0, 1
+; RV32IMB-NEXT:    li a3, 1
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preames wrote:

a) This test is really checking for a combine loop, and (b) zbs would produce a bset here and zba w/o zbs is mildly odd, and c) the overall better result would probably be (x*3+256)*8 (SH1ADD, ADDI, SHL) so we're not optimal either way.

So yes, but I don't think we care.

https://github.com/llvm/llvm-project/pull/88524