[PATCH] D111532: [RISCV] Optimize immediate materialisation with BCLRI

[Ben Shi via Phabricator via llvm-commits]

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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D111532

Files:
  llvm/lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp
  llvm/test/CodeGen/RISCV/imm.ll


Index: llvm/test/CodeGen/RISCV/imm.ll
===================================================================
--- llvm/test/CodeGen/RISCV/imm.ll
+++ llvm/test/CodeGen/RISCV/imm.ll
@@ -804,10 +804,9 @@
 ;
 ; RV64IB-LABEL: imm_neg_2863311530:
 ; RV64IB:       # %bb.0:
-; RV64IB-NEXT:    lui a0, 1048405
-; RV64IB-NEXT:    addiw a0, a0, 1365
-; RV64IB-NEXT:    slli a0, a0, 12
-; RV64IB-NEXT:    addi a0, a0, 1366
+; RV64IB-NEXT:    lui a0, 873813
+; RV64IB-NEXT:    addiw a0, a0, 1366
+; RV64IB-NEXT:    bclri a0, a0, 31
 ; RV64IB-NEXT:    ret
 	ret i64 -2863311530 ; #0xffffffff55555556
 }
Index: llvm/lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp
===================================================================
--- llvm/lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp
+++ llvm/lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp
@@ -182,6 +182,23 @@
     }
   }
 
+  // Optimize for values in range 0xffffffff 7fffffff ~ 0xffffffff 00000000.
+  // First call generateInstSeqImpl with Val+0x80000000 (which is an int32),
+  // then emit (BCLRI r, 31).
+  if (Res.size() > 3 && ActiveFeatures[RISCV::FeatureStdExtZbs]) {
+    assert(ActiveFeatures[RISCV::Feature64Bit] &&
+           "Expected RV32 to only need 2 instructions");
+    uint64_t UVal = Val;
+    if (0xffffffff00000000 <= UVal && UVal <= 0xffffffff7fffffff) {
+      RISCVMatInt::InstSeq TmpSeq;
+      generateInstSeqImpl(UVal + 0x80000000, ActiveFeatures, TmpSeq);
+      assert(TmpSeq.size <= 2 &&
+             "value outside range [0xffffffff7fffffff, 0xffffffff00000000]");
+      TmpSeq.push_back(RISCVMatInt::Inst(RISCV::BCLRI, 31));
+      return TmpSeq;
+    }
+  }
+
   return Res;
 }
 


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