[MachineCSE] Add an option to override the profitability heuristics

Differential Revision: https://reviews.llvm.org/D157002

llvm/lib/CodeGen/MachineCSE.cpp

@@ -65,6 +65,10 @@ static cl::opt<int>
     CSUsesThreshold("csuses-threshold", cl::Hidden, cl::init(1024),
                     cl::desc("Threshold for the size of CSUses"));
 
+static cl::opt<bool> AggressiveMachineCSE(
+    "aggressive-machine-cse", cl::Hidden, cl::init(false),
+    cl::desc("Override the profitability heuristics for Machine CSE"));
+
 namespace {
 
   class MachineCSE : public MachineFunctionPass {
@@ -439,6 +443,9 @@ bool MachineCSE::isCSECandidate(MachineInstr *MI) {
 /// defined.
 bool MachineCSE::isProfitableToCSE(Register CSReg, Register Reg,
                                    MachineBasicBlock *CSBB, MachineInstr *MI) {
+  if (AggressiveMachineCSE)
+    return true;
+
   // FIXME: Heuristics that works around the lack the live range splitting.
 
   // If CSReg is used at all uses of Reg, CSE should not increase register

llvm/test/CodeGen/AArch64/machine-cse-profitable-check.ll

@@ -0,0 +1,31 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 2
+; RUN: llc -mtriple aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK-BASE
+; RUN: llc -mtriple aarch64-none-linux-gnu -aggressive-machine-cse < %s | FileCheck %s --check-prefixes=CHECK-AGGRESSIVE-CSE
+
+define void @foo(ptr %buf, <8 x i16> %a) {
+; CHECK-BASE-LABEL: foo:
+; CHECK-BASE:       // %bb.0: // %entry
+; CHECK-BASE-NEXT:    movi v2.2d, #0000000000000000
+; CHECK-BASE-NEXT:    // kill: def $q0 killed $q0 def $q0_q1
+; CHECK-BASE-NEXT:    zip2 v2.8h, v0.8h, v2.8h
+; CHECK-BASE-NEXT:    movi v1.2d, #0000000000000000
+; CHECK-BASE-NEXT:    st2 { v0.4h, v1.4h }, [x0], #16
+; CHECK-BASE-NEXT:    str q2, [x0]
+; CHECK-BASE-NEXT:    ret
+;
+; CHECK-AGGRESSIVE-CSE-LABEL: foo:
+; CHECK-AGGRESSIVE-CSE:       // %bb.0: // %entry
+; CHECK-AGGRESSIVE-CSE-NEXT:    // kill: def $q0 killed $q0 def $q0_q1
+; CHECK-AGGRESSIVE-CSE-NEXT:    movi v1.2d, #0000000000000000
+; CHECK-AGGRESSIVE-CSE-NEXT:    st2 { v0.4h, v1.4h }, [x0], #16
+; CHECK-AGGRESSIVE-CSE-NEXT:    zip2 v0.8h, v0.8h, v1.8h
+; CHECK-AGGRESSIVE-CSE-NEXT:    str q0, [x0]
+; CHECK-AGGRESSIVE-CSE-NEXT:    ret
+entry:
+  %vzip.i = shufflevector <8 x i16> %a, <8 x i16> <i16 0, i16 0, i16 0, i16 0, i16 poison, i16 poison, i16 poison, i16 poison>, <8 x i32> <i32 0, i32 8, i32 1, i32 9, i32 2, i32 10, i32 3, i32 11>
+  %vzip1.i = shufflevector <8 x i16> %a, <8 x i16> <i16 poison, i16 poison, i16 poison, i16 poison, i16 0, i16 0, i16 0, i16 0>, <8 x i32> <i32 4, i32 12, i32 5, i32 13, i32 6, i32 14, i32 7, i32 15>
+  store <8 x i16> %vzip.i, ptr %buf, align 4
+  %add.ptr = getelementptr inbounds i32, ptr %buf, i64 4
+  store <8 x i16> %vzip1.i, ptr %add.ptr, align 4
+  ret void
+}