[RISCV] Split f64 undef into two i32 undefs

So that no store instruction will be generated.

Reviewed By: asb

Differential Revision: https://reviews.llvm.org/D118222

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index c6abad2..7dd56d4 100644 (file)
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -7796,6 +7796,12 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
     if (Op0->getOpcode() == RISCVISD::BuildPairF64)
       return DCI.CombineTo(N, Op0.getOperand(0), Op0.getOperand(1));
 
+    if (Op0->isUndef()) {
+      SDValue Lo = DAG.getUNDEF(MVT::i32);
+      SDValue Hi = DAG.getUNDEF(MVT::i32);
+      return DCI.CombineTo(N, Lo, Hi);
+    }
+
     SDLoc DL(N);
 
     // It's cheaper to materialise two 32-bit integers than to load a double

diff --git a/llvm/test/CodeGen/RISCV/double-calling-conv.ll b/llvm/test/CodeGen/RISCV/double-calling-conv.ll
index 4ec95aa..054cba1 100644 (file)
--- a/llvm/test/CodeGen/RISCV/double-calling-conv.ll
+++ b/llvm/test/CodeGen/RISCV/double-calling-conv.ll
@@ -146,11 +146,6 @@ define double @caller_double_stack() nounwind {
 define double @func_return_double_undef() nounwind {
 ; RV32IFD-LABEL: func_return_double_undef:
 ; RV32IFD:       # %bb.0:
-; RV32IFD-NEXT:    addi sp, sp, -16
-; RV32IFD-NEXT:    fsd ft0, 8(sp)
-; RV32IFD-NEXT:    lw a0, 8(sp)
-; RV32IFD-NEXT:    lw a1, 12(sp)
-; RV32IFD-NEXT:    addi sp, sp, 16
 ; RV32IFD-NEXT:    ret
   ret double undef
 }