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[LICM] Hoisting of widenable conditions out of loops

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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
This commit is contained in:
Philip Reames 2019-11-08 07:00:55 -08:00
parent 9054503f8d
commit 6539fe9696
3 changed files with 48 additions and 9 deletions
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2
include/llvm/IR/Intrinsics.td
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@ -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]>;

4
lib/Transforms/Scalar/LICM.cpp
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@ -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)

51
test/Transforms/LICM/explicit_guards.ll
View File

@ -2,21 +2,18 @@
; 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: [[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:
@ -44,15 +41,53 @@ 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:
; 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 @maythrow()
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_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: