[llvm] [CodeGenPrepare] Transform `shl X, cttz(Y)` to `mul (Y & -Y), X` if cttz is unsupported (PR #85066)

[Wang Pengcheng via llvm-commits]

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@@ -0,0 +1,832 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc -mtriple=riscv32 -mattr=+m -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s -check-prefix=RV32I
+; RUN: llc -mtriple=riscv32 -mattr=+m,+zbb -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s -check-prefix=RV32ZBB
+; RUN: llc -mtriple=riscv64 -mattr=+m -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s -check-prefixes=RV64I,RV64IILLEGALI32
+; RUN: llc -mtriple=riscv64 -mattr=+m,+zbb -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s -check-prefixes=RV64ZBB,RV64ZBBILLEGALI32
+; RUN: llc -mtriple=riscv64 -mattr=+m -riscv-experimental-rv64-legal-i32 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s -check-prefixes=RV64I,RV64ILEGALI32
+; RUN: llc -mtriple=riscv64 -mattr=+m,+zbb -riscv-experimental-rv64-legal-i32 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s -check-prefixes=RV64ZBB,RV64ZBBLEGALI32
+
+define i32 @shl_cttz_i32(i32 %x, i32 %y) {
+; RV32I-LABEL: shl_cttz_i32:
+; RV32I:       # %bb.0: # %entry
+; RV32I-NEXT:    neg a2, a1
+; RV32I-NEXT:    and a1, a1, a2
+; RV32I-NEXT:    mul a0, a1, a0
+; RV32I-NEXT:    ret
+;
+; RV32ZBB-LABEL: shl_cttz_i32:
+; RV32ZBB:       # %bb.0: # %entry
+; RV32ZBB-NEXT:    ctz a1, a1
+; RV32ZBB-NEXT:    sll a0, a0, a1
+; RV32ZBB-NEXT:    ret
+;
+; RV64IILLEGALI32-LABEL: shl_cttz_i32:
+; RV64IILLEGALI32:       # %bb.0: # %entry
+; RV64IILLEGALI32-NEXT:    negw a2, a1
+; RV64IILLEGALI32-NEXT:    and a1, a1, a2
+; RV64IILLEGALI32-NEXT:    lui a2, 30667
+; RV64IILLEGALI32-NEXT:    addi a2, a2, 1329
+; RV64IILLEGALI32-NEXT:    mul a1, a1, a2
+; RV64IILLEGALI32-NEXT:    srliw a1, a1, 27
+; RV64IILLEGALI32-NEXT:    lui a2, %hi(.LCPI0_0)
+; RV64IILLEGALI32-NEXT:    addi a2, a2, %lo(.LCPI0_0)
+; RV64IILLEGALI32-NEXT:    add a1, a2, a1
+; RV64IILLEGALI32-NEXT:    lbu a1, 0(a1)
+; RV64IILLEGALI32-NEXT:    sllw a0, a0, a1
+; RV64IILLEGALI32-NEXT:    ret
+;
+; RV64ZBB-LABEL: shl_cttz_i32:
+; RV64ZBB:       # %bb.0: # %entry
+; RV64ZBB-NEXT:    ctzw a1, a1
+; RV64ZBB-NEXT:    sllw a0, a0, a1
+; RV64ZBB-NEXT:    ret
+;
+; RV64ILEGALI32-LABEL: shl_cttz_i32:
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wangpc-pp wrote:

It seems there is a huge gain when i32 is legal, maybe we should put legalizing i32 on our agenda in the next release cycle? cc @topperc  @asb

https://github.com/llvm/llvm-project/pull/85066