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

[Craig Topper via llvm-commits]

https://github.com/topperc created https://github.com/llvm/llvm-project/pull/106653

None

>From 153bc353f059ddf94c4e1e78f6eb9ed90770f257 Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper at sifive.com>
Date: Thu, 29 Aug 2024 19:08:31 -0700
Subject: [PATCH] [RISCV] Add constant folding combine for FMV_X_ANYEXTW/H.

---
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp  |  7 +++++++
 llvm/test/CodeGen/RISCV/calling-conv-half.ll |  9 +++------
 llvm/test/CodeGen/RISCV/float-imm.ll         |  4 ++--
 llvm/test/CodeGen/RISCV/half-imm.ll          | 14 ++++----------
 4 files changed, 16 insertions(+), 18 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 09928dcc1f489a..33bc4b063bbb48 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/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.
diff --git a/llvm/test/CodeGen/RISCV/calling-conv-half.ll b/llvm/test/CodeGen/RISCV/calling-conv-half.ll
index c88b2bf596ca23..cccb69d2e6986a 100644
--- a/llvm/test/CodeGen/RISCV/calling-conv-half.ll
+++ b/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:
diff --git a/llvm/test/CodeGen/RISCV/float-imm.ll b/llvm/test/CodeGen/RISCV/float-imm.ll
index c38416d994ba57..69a506cd850f2c 100644
--- a/llvm/test/CodeGen/RISCV/float-imm.ll
+++ b/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
 }
diff --git a/llvm/test/CodeGen/RISCV/half-imm.ll b/llvm/test/CodeGen/RISCV/half-imm.ll
index 9c11010540e15d..f2292b656a304f 100644
--- a/llvm/test/CodeGen/RISCV/half-imm.ll
+++ b/llvm/test/CodeGen/RISCV/half-imm.ll
@@ -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:
@@ -45,12 +45,6 @@ define half @half_imm() nounwind {
 ; CHECKIZFHMIN-NEXT:    lui a0, %hi(.LCPI0_0)
 ; 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
   ret half 3.0
 }