[llvm] [RISCV] Disable constant hoisting for mul by one more/less than a pow… (PR #67385)

[Wang Pengcheng via llvm-commits]

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@@ -127,6 +127,9 @@ InstructionCost RISCVTTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
     // Power of 2 is a shift. Negated power of 2 is a shift and a negate.
     if (Imm.isPowerOf2() || Imm.isNegatedPowerOf2())
       return TTI::TCC_Free;
+    // One more or less than a power of 2 can use SLLI+ADD/SUB.
+    if ((Imm + 1).isPowerOf2() || (Imm - 1).isPowerOf2())
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wangpc-pp wrote:

What about negative values? It needs 3 instructions I think, would it be worthy too?

https://github.com/llvm/llvm-project/pull/67385