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

[Ben Shi via Phabricator via llvm-commits]

benshi001 updated this revision to Diff 378617.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D111532/new/

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 +182,22 @@
     }
   }
 
+  // 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() > 2 && ActiveFeatures[RISCV::FeatureStdExtZbs]) {
+    assert(ActiveFeatures[RISCV::Feature64Bit] &&
+           "Expected RV32 to only need 2 instructions");
+    int64_t NewVal = Val + 0x80000000;
+    if (NewVal < 0 && isInt<32>(NewVal)) {
+      RISCVMatInt::InstSeq TmpSeq;
+      generateInstSeqImpl(NewVal, ActiveFeatures, TmpSeq);
+      TmpSeq.push_back(RISCVMatInt::Inst(RISCV::BCLRI, 31));
+      if (TmpSeq.size() < Res.size())
+        return TmpSeq;
+    }
+  }
+
   return Res;
 }
 


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