[RISCV] Add constant folding combine for FMV_X_ANYEXTW/H. (llvm#106653)

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -16440,6 +16440,13 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
     SDLoc DL(N);
     SDValue Op0 = N->getOperand(0);
     MVT VT = N->getSimpleValueType(0);
+
+    // Constant fold.
+    if (auto *CFP = dyn_cast<ConstantFPSDNode>(Op0)) {
+      APInt Val = CFP->getValueAPF().bitcastToAPInt().sext(VT.getSizeInBits());
+      return DAG.getConstant(Val, DL, VT);
+    }
+
     // If the input to FMV_X_ANYEXTW_RV64 is just FMV_W_X_RV64 then the
     // conversion is unnecessary and can be replaced with the FMV_W_X_RV64
     // operand. Similar for FMV_X_ANYEXTH and FMV_H_X.

llvm/test/CodeGen/RISCV/calling-conv-half.ll

@@ -161,10 +161,8 @@ define i32 @caller_half_in_regs() nounwind {
 ; RV64IF:       # %bb.0:
 ; RV64IF-NEXT:    addi sp, sp, -16
 ; RV64IF-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
-; RV64IF-NEXT:    lui a0, 1048564
-; RV64IF-NEXT:    fmv.w.x fa5, a0
-; RV64IF-NEXT:    fmv.x.w a1, fa5
 ; RV64IF-NEXT:    li a0, 1
+; RV64IF-NEXT:    lui a1, 1048564
 ; RV64IF-NEXT:    call callee_half_in_regs
 ; RV64IF-NEXT:    ld ra, 8(sp) # 8-byte Folded Reload
 ; RV64IF-NEXT:    addi sp, sp, 16
@@ -511,9 +509,8 @@ define half @callee_half_ret() nounwind {
 ;
 ; RV64IF-LABEL: callee_half_ret:
 ; RV64IF:       # %bb.0:
-; RV64IF-NEXT:    lui a0, %hi(.LCPI4_0)
-; RV64IF-NEXT:    flw fa5, %lo(.LCPI4_0)(a0)
-; RV64IF-NEXT:    fmv.x.w a0, fa5
+; RV64IF-NEXT:    lui a0, 1048564
+; RV64IF-NEXT:    addiw a0, a0, -1024
 ; RV64IF-NEXT:    ret
 ;
 ; RV32-ILP32F-LABEL: callee_half_ret:

llvm/test/CodeGen/RISCV/float-imm.ll

@@ -24,8 +24,8 @@ define float @float_imm() nounwind {
 ;
 ; RV64ZFINX-LABEL: float_imm:
 ; RV64ZFINX:       # %bb.0:
-; RV64ZFINX-NEXT:    lui a0, %hi(.LCPI0_0)
-; RV64ZFINX-NEXT:    lw a0, %lo(.LCPI0_0)(a0)
+; RV64ZFINX-NEXT:    lui a0, 263313
+; RV64ZFINX-NEXT:    addiw a0, a0, -37
 ; RV64ZFINX-NEXT:    ret
   ret float 3.14159274101257324218750
 }

llvm/test/CodeGen/RISCV/half-imm.ll

@@ -15,10 +15,10 @@
 ; RUN:   -target-abi lp64f < %s | FileCheck -check-prefixes=CHECKIZFHMIN %s
 ; RUN: llc -mtriple=riscv32 -mattr=+zhinxmin -verify-machineinstrs \
 ; RUN:   -target-abi ilp32 < %s \
-; RUN:   | FileCheck -check-prefixes=CHECKIZHINXMIN %s
+; RUN:   | FileCheck -check-prefixes=CHECKIZHINXMIN,RV32IZHINXMIN %s
 ; RUN: llc -mtriple=riscv64 -mattr=+zhinxmin -verify-machineinstrs \
 ; RUN:   -target-abi lp64 < %s \
-; RUN:   | FileCheck -check-prefixes=CHECKIZHINXMIN %s
+; RUN:   | FileCheck -check-prefixes=CHECKIZHINXMIN,RV64IZHINXMIN %s
 
 ; TODO: constant pool shouldn't be necessary for RV32IZfh and RV64IZfh
 define half @half_imm() nounwind {
@@ -30,14 +30,14 @@ define half @half_imm() nounwind {
 ;
 ; RV32IZHINX-LABEL: half_imm:
 ; RV32IZHINX:       # %bb.0:
-; RV32IZHINX-NEXT:    lui a0, %hi(.LCPI0_0)
-; RV32IZHINX-NEXT:    lh a0, %lo(.LCPI0_0)(a0)
+; RV32IZHINX-NEXT:    lui a0, 4
+; RV32IZHINX-NEXT:    addi a0, a0, 512
 ; RV32IZHINX-NEXT:    ret
 ;
 ; RV64IZHINX-LABEL: half_imm:
 ; RV64IZHINX:       # %bb.0:
-; RV64IZHINX-NEXT:    lui a0, %hi(.LCPI0_0)
-; RV64IZHINX-NEXT:    lh a0, %lo(.LCPI0_0)(a0)
+; RV64IZHINX-NEXT:    lui a0, 4
+; RV64IZHINX-NEXT:    addiw a0, a0, 512
 ; RV64IZHINX-NEXT:    ret
 ;
 ; CHECKIZFHMIN-LABEL: half_imm:
@@ -46,11 +46,17 @@ define half @half_imm() nounwind {
 ; CHECKIZFHMIN-NEXT:    flh fa0, %lo(.LCPI0_0)(a0)
 ; CHECKIZFHMIN-NEXT:    ret
 ;
-; CHECKIZHINXMIN-LABEL: half_imm:
-; CHECKIZHINXMIN:       # %bb.0:
-; CHECKIZHINXMIN-NEXT:    lui a0, %hi(.LCPI0_0)
-; CHECKIZHINXMIN-NEXT:    lh a0, %lo(.LCPI0_0)(a0)
-; CHECKIZHINXMIN-NEXT:    ret
+; RV32IZHINXMIN-LABEL: half_imm:
+; RV32IZHINXMIN:       # %bb.0:
+; RV32IZHINXMIN-NEXT:    lui a0, 4
+; RV32IZHINXMIN-NEXT:    addi a0, a0, 512
+; RV32IZHINXMIN-NEXT:    ret
+;
+; RV64IZHINXMIN-LABEL: half_imm:
+; RV64IZHINXMIN:       # %bb.0:
+; RV64IZHINXMIN-NEXT:    lui a0, 4
+; RV64IZHINXMIN-NEXT:    addiw a0, a0, 512
+; RV64IZHINXMIN-NEXT:    ret
   ret half 3.0
 }