Commit 787dba7a authored by Philip Reames's avatar Philip Reames
Browse files

[LICM] Hoisting of widenable conditions out of loops 

The change itself is straight forward and obvious, but ... there's an existing test checking for exactly the opposite. Both I and Artur think this is simply conservatism in the initial implementation.  If anyone bisects a problem to this, a counter example will be very interesting.

Differential Revision: https://reviews.llvm.org/D69907
parent 0703db39

llvm/include/llvm/IR/Intrinsics.td

+1 −1
Original line number Diff line number Diff line
@@ -1070,7 +1070,7 @@ def int_experimental_guard : Intrinsic<[], [llvm_i1_ty, llvm_vararg_ty], 


// Supports widenable conditions for guards represented as explicit branches.

def int_experimental_widenable_condition : Intrinsic<[llvm_i1_ty], [],

                                           [IntrInaccessibleMemOnly, IntrWillReturn]>;

        [IntrInaccessibleMemOnly, IntrWillReturn, IntrSpeculatable]>;



// NOP: calls/invokes to this intrinsic are removed by codegen

def int_donothing : Intrinsic<[], [], [IntrNoMem, IntrWillReturn]>;

llvm/lib/Transforms/Scalar/LICM.cpp

+4 −0
Original line number Diff line number Diff line
@@ -1144,6 +1144,10 @@ bool llvm::canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT, 
      // Assumes don't actually alias anything or throw

      return true;



    if (match(CI, m_Intrinsic<Intrinsic::experimental_widenable_condition>()))

      // Widenable conditions don't actually alias anything or throw

      return true;



    // Handle simple cases by querying alias analysis.

    FunctionModRefBehavior Behavior = AA->getModRefBehavior(CI);

    if (Behavior == FMRB_DoesNotAccessMemory)

llvm/test/Transforms/LICM/explicit_guards.ll

+42 −7
Original line number Diff line number Diff line
@@ -2,21 +2,54 @@ 
; RUN: opt -S -make-guards-explicit -basicaa -licm < %s        | FileCheck %s

; RUN: opt -S -aa-pipeline=basic-aa -passes='require<opt-remark-emit>,make-guards-explicit,loop(licm)' < %s | FileCheck %s



; Test interaction between explicit guards and LICM: make sure that we do not

; hoist explicit conditions while we can hoist invariant loads in presence of

; explicit guards.



declare void @llvm.experimental.guard(i1,...)

declare void @maythrow()



; Make sure that we do not hoist widenable_cond out of loop.

define void @do_not_hoist_widenable_cond(i1 %cond, i32 %N, i32 %M) {

; CHECK-LABEL: @do_not_hoist_widenable_cond(

define void @hoist_widenable_cond(i1 %cond, i32 %N, i32 %M) {

; CHECK-LABEL: @hoist_widenable_cond(

; CHECK-NEXT:  entry:

; CHECK-NEXT:    [[WIDENABLE_COND:%.*]] = call i1 @llvm.experimental.widenable.condition()

; CHECK-NEXT:    br label [[LOOP:%.*]]

; CHECK:       loop:

; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[GUARDED:%.*]] ]

; CHECK-NEXT:    [[GUARD_COND:%.*]] = icmp slt i32 [[IV]], [[N:%.*]]

; CHECK-NEXT:    [[EXIPLICIT_GUARD_COND:%.*]] = and i1 [[GUARD_COND]], [[WIDENABLE_COND]]

; CHECK-NEXT:    br i1 [[EXIPLICIT_GUARD_COND]], label [[GUARDED]], label [[DEOPT:%.*]], !prof !0

; CHECK:       deopt:

; CHECK-NEXT:    call void (...) @llvm.experimental.deoptimize.isVoid() [ "deopt"() ]

; CHECK-NEXT:    ret void

; CHECK:       guarded:

; CHECK-NEXT:    [[LOOP_COND:%.*]] = icmp slt i32 [[IV]], [[M:%.*]]

; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1

; CHECK-NEXT:    br i1 [[LOOP_COND]], label [[LOOP]], label [[EXIT:%.*]]

; CHECK:       exit:

; CHECK-NEXT:    ret void

;

entry:

  br label %loop



loop:

  %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]

  %guard_cond = icmp slt i32 %iv, %N

  call void(i1, ...) @llvm.experimental.guard(i1 %guard_cond) [ "deopt"() ]

  %loop_cond = icmp slt i32 %iv, %M

  %iv.next = add i32 %iv, 1

  br i1 %loop_cond, label %loop, label %exit



exit:

  ret void

}



define void @hoist_widenable_cond_speculate(i1 %cond, i32 %N, i32 %M) {

; CHECK-LABEL: @hoist_widenable_cond_speculate(

; CHECK-NEXT:  entry:

; CHECK-NEXT:    [[WIDENABLE_COND:%.*]] = call i1 @llvm.experimental.widenable.condition()

; CHECK-NEXT:    br label [[LOOP:%.*]]

; CHECK:       loop:

; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[GUARDED:%.*]] ]

; CHECK-NEXT:    [[GUARD_COND:%.*]] = icmp slt i32 [[IV]], [[N:%.*]]

; CHECK-NEXT:    call void @maythrow()

; CHECK-NEXT:    [[EXIPLICIT_GUARD_COND:%.*]] = and i1 [[GUARD_COND]], [[WIDENABLE_COND]]

; CHECK-NEXT:    br i1 [[EXIPLICIT_GUARD_COND]], label [[GUARDED]], label [[DEOPT:%.*]], !prof !0

; CHECK:       deopt:
@@ -35,6 +68,7 @@ entry: 
loop:

  %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]

  %guard_cond = icmp slt i32 %iv, %N

  call void @maythrow()

  call void(i1, ...) @llvm.experimental.guard(i1 %guard_cond) [ "deopt"() ]

  %loop_cond = icmp slt i32 %iv, %M

  %iv.next = add i32 %iv, 1
@@ -44,15 +78,16 @@ exit: 
  ret void

}





define void @hoist_invariant_load(i1 %cond, i32* %np, i32 %M) {

; CHECK-LABEL: @hoist_invariant_load(

; CHECK-NEXT:  entry:

; CHECK-NEXT:    [[N:%.*]] = load i32, i32* [[NP:%.*]]

; CHECK-NEXT:    [[WIDENABLE_COND:%.*]] = call i1 @llvm.experimental.widenable.condition()

; CHECK-NEXT:    br label [[LOOP:%.*]]

; CHECK:       loop:

; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[GUARDED:%.*]] ]

; CHECK-NEXT:    [[GUARD_COND:%.*]] = icmp slt i32 [[IV]], [[N]]

; CHECK-NEXT:    [[WIDENABLE_COND:%.*]] = call i1 @llvm.experimental.widenable.condition()

; CHECK-NEXT:    [[EXIPLICIT_GUARD_COND:%.*]] = and i1 [[GUARD_COND]], [[WIDENABLE_COND]]

; CHECK-NEXT:    br i1 [[EXIPLICIT_GUARD_COND]], label [[GUARDED]], label [[DEOPT:%.*]], !prof !0

; CHECK:       deopt: