[RISCV] Optimize x > 1 ? x : 1 -> x > 0 ? x : 1

if x == 1,
  x > 1 ? x : 1  return x, which is also 1.
  x > 0 ? x : 1  return 1.

Reduce the number of load 1 instructions.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D132211

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index d0d48c0..800c529 100644 (file)
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -4083,6 +4083,12 @@ SDValue RISCVTargetLowering::lowerSELECT(SDValue Op, SelectionDAG &DAG) const {
     }
 
     translateSetCCForBranch(DL, LHS, RHS, CCVal, DAG);
+    // 1 < x ? x : 1 -> 0 < x ? x : 1
+    if (isOneConstant(LHS) && !isa<ConstantSDNode>(RHS) &&
+        (CCVal == ISD::SETLT || CCVal == ISD::SETULT) && RHS == TrueV &&
+        isOneConstant(FalseV)) {
+      LHS = DAG.getConstant(0, DL, VT);
+    }
 
     SDValue TargetCC = DAG.getCondCode(CCVal);
     SDValue Ops[] = {LHS, RHS, TargetCC, TrueV, FalseV};

diff --git a/llvm/test/CodeGen/RISCV/forced-atomics.ll b/llvm/test/CodeGen/RISCV/forced-atomics.ll
index fc03091..d8b33fe 100644 (file)
--- a/llvm/test/CodeGen/RISCV/forced-atomics.ll
+++ b/llvm/test/CodeGen/RISCV/forced-atomics.ll
@@ -995,9 +995,8 @@ define i32 @rmw32_max_seq_cst(ptr %p) nounwind {
 ; RV32-NO-ATOMIC-NEXT:    bnez a0, .LBB23_4
 ; RV32-NO-ATOMIC-NEXT:  .LBB23_2: # %atomicrmw.start
 ; RV32-NO-ATOMIC-NEXT:    # =>This Inner Loop Header: Depth=1
-; RV32-NO-ATOMIC-NEXT:    li a0, 1
 ; RV32-NO-ATOMIC-NEXT:    mv a2, a1
-; RV32-NO-ATOMIC-NEXT:    blt a0, a1, .LBB23_1
+; RV32-NO-ATOMIC-NEXT:    bgtz a1, .LBB23_1
 ; RV32-NO-ATOMIC-NEXT:  # %bb.3: # %atomicrmw.start
 ; RV32-NO-ATOMIC-NEXT:    # in Loop: Header=BB23_2 Depth=1
 ; RV32-NO-ATOMIC-NEXT:    li a2, 1
@@ -1183,9 +1182,8 @@ define i32 @rmw32_umax_seq_cst(ptr %p) nounwind {
 ; RV32-NO-ATOMIC-NEXT:    bnez a0, .LBB25_4
 ; RV32-NO-ATOMIC-NEXT:  .LBB25_2: # %atomicrmw.start
 ; RV32-NO-ATOMIC-NEXT:    # =>This Inner Loop Header: Depth=1
-; RV32-NO-ATOMIC-NEXT:    li a0, 1
 ; RV32-NO-ATOMIC-NEXT:    mv a2, a1
-; RV32-NO-ATOMIC-NEXT:    bltu a0, a1, .LBB25_1
+; RV32-NO-ATOMIC-NEXT:    bltu zero, a1, .LBB25_1
 ; RV32-NO-ATOMIC-NEXT:  # %bb.3: # %atomicrmw.start
 ; RV32-NO-ATOMIC-NEXT:    # in Loop: Header=BB25_2 Depth=1
 ; RV32-NO-ATOMIC-NEXT:    li a2, 1
@@ -2563,9 +2561,8 @@ define i64 @rmw64_max_seq_cst(ptr %p) nounwind {
 ; RV64-NO-ATOMIC-NEXT:    bnez a0, .LBB49_4
 ; RV64-NO-ATOMIC-NEXT:  .LBB49_2: # %atomicrmw.start
 ; RV64-NO-ATOMIC-NEXT:    # =>This Inner Loop Header: Depth=1
-; RV64-NO-ATOMIC-NEXT:    li a0, 1
 ; RV64-NO-ATOMIC-NEXT:    mv a2, a1
-; RV64-NO-ATOMIC-NEXT:    blt a0, a1, .LBB49_1
+; RV64-NO-ATOMIC-NEXT:    bgtz a1, .LBB49_1
 ; RV64-NO-ATOMIC-NEXT:  # %bb.3: # %atomicrmw.start
 ; RV64-NO-ATOMIC-NEXT:    # in Loop: Header=BB49_2 Depth=1
 ; RV64-NO-ATOMIC-NEXT:    li a2, 1
@@ -2756,9 +2753,8 @@ define i64 @rmw64_umax_seq_cst(ptr %p) nounwind {
 ; RV64-NO-ATOMIC-NEXT:    bnez a0, .LBB51_4
 ; RV64-NO-ATOMIC-NEXT:  .LBB51_2: # %atomicrmw.start
 ; RV64-NO-ATOMIC-NEXT:    # =>This Inner Loop Header: Depth=1
-; RV64-NO-ATOMIC-NEXT:    li a0, 1
 ; RV64-NO-ATOMIC-NEXT:    mv a2, a1
-; RV64-NO-ATOMIC-NEXT:    bltu a0, a1, .LBB51_1
+; RV64-NO-ATOMIC-NEXT:    bltu zero, a1, .LBB51_1
 ; RV64-NO-ATOMIC-NEXT:  # %bb.3: # %atomicrmw.start
 ; RV64-NO-ATOMIC-NEXT:    # in Loop: Header=BB51_2 Depth=1
 ; RV64-NO-ATOMIC-NEXT:    li a2, 1