From 75c64c7c4e40ec9bc16d90fee46353628d08d62d Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper@sifive.com>
Date: Fri, 5 Aug 2022 12:41:28 -0700
Subject: [RISCV] Don't use li+sh3add for constants that can use lui+add.

If we're adding a constant that can't use addi we try a few tricks,
one of which is using li+sh3add. We should not do this if lui+add
would work. For example adding 8192. Using sh3add prevents folding
a sext.w to form addw, thus increasing instruction count.
---
 llvm/lib/Target/RISCV/RISCVInstrInfoZb.td |  8 ++++----
 llvm/test/CodeGen/RISCV/rv32zba.ll        | 10 ++++++++++
 llvm/test/CodeGen/RISCV/rv64zba.ll        | 22 ++++++++++++++++++++++
 3 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoZb.td b/llvm/lib/Target/RISCV/RISCVInstrInfoZb.td
index 72122d6e8830..1a7539f40d47 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoZb.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoZb.td
@@ -237,17 +237,17 @@ def CSImm12MulBy4 : PatLeaf<(imm), [{
   if (!N->hasOneUse())
     return false;
   int64_t C = N->getSExtValue();
-  // Skip if C is simm12 or can be optimized by the PatLeaf AddiPair.
-  return !isInt<13>(C) && isShiftedInt<12, 2>(C);
+  // Skip if C is simm12, an lui, or can be optimized by the PatLeaf AddiPair.
+  return !isInt<13>(C) && !isShiftedInt<20, 12>(C) && isShiftedInt<12, 2>(C);
 }]>;
 
 def CSImm12MulBy8 : PatLeaf<(imm), [{
   if (!N->hasOneUse())
     return false;
   int64_t C = N->getSExtValue();
-  // Skip if C is simm12 or can be optimized by the PatLeaf AddiPair or
+  // Skip if C is simm12, an lui or can be optimized by the PatLeaf AddiPair or
   // CSImm12MulBy4.
-  return !isInt<14>(C) && isShiftedInt<12, 3>(C);
+  return !isInt<14>(C) && !isShiftedInt<20, 12>(C) && isShiftedInt<12, 3>(C);
 }]>;
 
 def SimmShiftRightBy2XForm : SDNodeXForm<imm, [{
diff --git a/llvm/test/CodeGen/RISCV/rv32zba.ll b/llvm/test/CodeGen/RISCV/rv32zba.ll
index 35b0920552a5..f39fa6a625b8 100644
--- a/llvm/test/CodeGen/RISCV/rv32zba.ll
+++ b/llvm/test/CodeGen/RISCV/rv32zba.ll
@@ -561,6 +561,16 @@ define i32 @add8208(i32 %a) {
   ret i32 %c
 }
 
+define i32 @add8192(i32 %a) {
+; CHECK-LABEL: add8192:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lui a1, 2
+; CHECK-NEXT:    add a0, a0, a1
+; CHECK-NEXT:    ret
+  %c = add i32 %a, 8192
+  ret i32 %c
+}
+
 define i32 @addshl_5_6(i32 %a, i32 %b) {
 ; RV32I-LABEL: addshl_5_6:
 ; RV32I:       # %bb.0:
diff --git a/llvm/test/CodeGen/RISCV/rv64zba.ll b/llvm/test/CodeGen/RISCV/rv64zba.ll
index 0ba17412ce8c..cd03b23af9fc 100644
--- a/llvm/test/CodeGen/RISCV/rv64zba.ll
+++ b/llvm/test/CodeGen/RISCV/rv64zba.ll
@@ -1116,6 +1116,28 @@ define i64 @add8208(i64 %a) {
   ret i64 %c
 }
 
+; Make sure we prefer LUI for the 8192 instead of using sh3add.
+define signext i32 @add8192_i32(i32 signext %a) {
+; CHECK-LABEL: add8192_i32:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lui a1, 2
+; CHECK-NEXT:    addw a0, a0, a1
+; CHECK-NEXT:    ret
+  %c = add i32 %a, 8192
+  ret i32 %c
+}
+
+; Make sure we prefer LUI for the 8192 instead of using sh3add.
+define i64 @add8192(i64 %a) {
+; CHECK-LABEL: add8192:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lui a1, 2
+; CHECK-NEXT:    add a0, a0, a1
+; CHECK-NEXT:    ret
+  %c = add i64 %a, 8192
+  ret i64 %c
+}
+
 define signext i32 @addshl32_5_6(i32 signext %a, i32 signext %b) {
 ; RV64I-LABEL: addshl32_5_6:
 ; RV64I:       # %bb.0:
-- 
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