[llvm] r356494 - Allow unordered loads to be considered invariant in CodeGen

[Philip Reames via llvm-commits]

Author: reames
Date: Tue Mar 19 11:27:18 2019
New Revision: 356494

URL: http://llvm.org/viewvc/llvm-project?rev=356494&view=rev
Log:
Allow unordered loads to be considered invariant in CodeGen

The actual code change is fairly straight forward, but exercising it isn't. First, it turned out we weren't adding the appropriate flags in SelectionDAG. Second, it turned out that we've got some optimization gaps, so obvious test cases don't work.

My first attempt (in atomic-unordered.ll) points out a deficiency in our peephole-opt folding logic which I plan to fix separately. Instead, I'm exercising this through MachineLICM.

Differential Revision: https://reviews.llvm.org/D59375


Modified:
    llvm/trunk/lib/CodeGen/MachineInstr.cpp
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
    llvm/trunk/test/CodeGen/X86/atomic-unordered.ll
    llvm/trunk/test/CodeGen/X86/hoist-invariant-load.ll

Modified: llvm/trunk/lib/CodeGen/MachineInstr.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineInstr.cpp?rev=356494&r1=356493&r2=356494&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineInstr.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineInstr.cpp Tue Mar 19 11:27:18 2019
@@ -1312,9 +1312,11 @@ bool MachineInstr::isDereferenceableInva
   const MachineFrameInfo &MFI = getParent()->getParent()->getFrameInfo();
 
   for (MachineMemOperand *MMO : memoperands()) {
-    if (MMO->isVolatile()) return false;
-    // TODO: Figure out whether isAtomic is really necessary (see D57601).
-    if (MMO->isAtomic()) return false;
+    if (!MMO->isUnordered())
+      // If the memory operand has ordering side effects, we can't move the
+      // instruction.  Such an instruction is technically an invariant load,
+      // but the caller code would need updated to expect that.
+      return false;
     if (MMO->isStore()) return false;
     if (MMO->isInvariant() && MMO->isDereferenceable())
       continue;

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp?rev=356494&r1=356493&r2=356494&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Tue Mar 19 11:27:18 2019
@@ -4564,6 +4564,11 @@ void SelectionDAGBuilder::visitAtomicLoa
   auto Flags = MachineMemOperand::MOLoad;
   if (I.isVolatile())
     Flags |= MachineMemOperand::MOVolatile;
+  if (I.getMetadata(LLVMContext::MD_invariant_load) != nullptr)
+    Flags |= MachineMemOperand::MOInvariant;
+  if (isDereferenceablePointer(I.getPointerOperand(), DAG.getDataLayout()))
+    Flags |= MachineMemOperand::MODereferenceable;
+
   Flags |= TLI.getMMOFlags(I);
 
   MachineMemOperand *MMO =

Modified: llvm/trunk/test/CodeGen/X86/atomic-unordered.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/atomic-unordered.ll?rev=356494&r1=356493&r2=356494&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/atomic-unordered.ll (original)
+++ llvm/trunk/test/CodeGen/X86/atomic-unordered.ll Tue Mar 19 11:27:18 2019
@@ -2546,7 +2546,7 @@ define i64 @fold_constant_fence(i64 %arg
   ret i64 %ret
 }
 
-define i64 @fold_invariant_clobber(i64* %p, i64 %arg) {
+define i64 @fold_invariant_clobber(i64* dereferenceable(8) %p, i64 %arg) {
 ; CHECK-O0-LABEL: fold_invariant_clobber:
 ; CHECK-O0:       # %bb.0:
 ; CHECK-O0-NEXT:    movq (%rdi), %rax
@@ -2567,7 +2567,7 @@ define i64 @fold_invariant_clobber(i64*
 }
 
 
-define i64 @fold_invariant_fence(i64* %p, i64 %arg) {
+define i64 @fold_invariant_fence(i64* dereferenceable(8) %p, i64 %arg) {
 ; CHECK-O0-LABEL: fold_invariant_fence:
 ; CHECK-O0:       # %bb.0:
 ; CHECK-O0-NEXT:    movq (%rdi), %rdi

Modified: llvm/trunk/test/CodeGen/X86/hoist-invariant-load.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/hoist-invariant-load.ll?rev=356494&r1=356493&r2=356494&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/hoist-invariant-load.ll (original)
+++ llvm/trunk/test/CodeGen/X86/hoist-invariant-load.ll Tue Mar 19 11:27:18 2019
@@ -73,27 +73,35 @@ define void @test_unordered(i8* %x) uwta
 ; CHECK:       ## %bb.0: ## %entry
 ; CHECK-NEXT:    pushq %rbp
 ; CHECK-NEXT:    .cfi_def_cfa_offset 16
-; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    pushq %r15
 ; CHECK-NEXT:    .cfi_def_cfa_offset 24
-; CHECK-NEXT:    pushq %rbx
+; CHECK-NEXT:    pushq %r14
 ; CHECK-NEXT:    .cfi_def_cfa_offset 32
-; CHECK-NEXT:    .cfi_offset %rbx, -32
-; CHECK-NEXT:    .cfi_offset %r14, -24
+; CHECK-NEXT:    pushq %rbx
+; CHECK-NEXT:    .cfi_def_cfa_offset 40
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    .cfi_offset %rbx, -40
+; CHECK-NEXT:    .cfi_offset %r14, -32
+; CHECK-NEXT:    .cfi_offset %r15, -24
 ; CHECK-NEXT:    .cfi_offset %rbp, -16
 ; CHECK-NEXT:    movq %rdi, %rbx
 ; CHECK-NEXT:    movl $10000, %ebp ## imm = 0x2710
-; CHECK-NEXT:    movq _objc_msgSend@{{.*}}(%rip), %r14
+; CHECK-NEXT:    movq {{.*}}(%rip), %r14
+; CHECK-NEXT:    movq _objc_msgSend@{{.*}}(%rip), %r15
 ; CHECK-NEXT:    .p2align 4, 0x90
 ; CHECK-NEXT:  LBB1_1: ## %for.body
 ; CHECK-NEXT:    ## =>This Inner Loop Header: Depth=1
-; CHECK-NEXT:    movq {{.*}}(%rip), %rsi
 ; CHECK-NEXT:    movq %rbx, %rdi
-; CHECK-NEXT:    callq *%r14
+; CHECK-NEXT:    movq %r14, %rsi
+; CHECK-NEXT:    callq *%r15
 ; CHECK-NEXT:    decl %ebp
 ; CHECK-NEXT:    jne LBB1_1
 ; CHECK-NEXT:  ## %bb.2: ## %for.end
+; CHECK-NEXT:    addq $8, %rsp
 ; CHECK-NEXT:    popq %rbx
 ; CHECK-NEXT:    popq %r14
+; CHECK-NEXT:    popq %r15
 ; CHECK-NEXT:    popq %rbp
 ; CHECK-NEXT:    retq
 entry: