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[SVEV] Recognise hardware-loop intrinsic loop.decrement.reg

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Teach SCEV about the @loop.decrement.reg intrinsic, which has exactly the same
semantics as a sub expression. This allows us to query hardware-loops, which
contain this @loop.decrement.reg intrinsic, so that we can calculate iteration
counts, exit values, etc. of hardwareloops.

This "int_loop_decrement_reg" intrinsic is defined as "IntrNoDuplicate". Thus,
while hardware-loops and tripcounts now become analysable by SCEV, this
prevents the usual loop transformations from applying transformations on
hardware-loops, which is what we want at this point, for which I have added
test cases for loopunrolling and IndVarSimplify and LFTR.

Differential Revision: https://reviews.llvm.org/D71563
This commit is contained in:
Sjoerd Meijer 2020-01-10 09:30:02 +00:00
parent 346de9b672
commit 67bf9a6154
4 changed files with 108 additions and 0 deletions
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11
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -4507,6 +4507,17 @@ static Optional<BinaryOp> MatchBinaryOp(Value *V, DominatorTree &DT) {
if (!Op)
return None;
// Recognise intrinsic loop.decrement.reg, and as this has exactly the same
// semantics as a Sub, return a binary sub expression.
if (auto *II = dyn_cast<IntrinsicInst>(V)) {
switch (II->getIntrinsicID()) {
case Intrinsic::loop_decrement_reg:
return BinaryOp(Instruction::Sub, II->getOperand(0), II->getOperand(1));
default:
return None;
}
}
// Implementation detail: all the cleverness here should happen without
// creating new SCEV expressions -- our caller knowns tricks to avoid creating
// SCEV expressions when possible, and we should not break that.

29
llvm/test/Transforms/IndVarSimplify/lftr.ll
View File

@ -153,6 +153,34 @@ loopexit:
ret i32 %i
}
define i32 @quadratic_sgt_loopdec() {
; CHECK-LABEL: @quadratic_sgt_loopdec(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[I:%.*]] = phi i32 [ 10, [[ENTRY:%.*]] ], [ [[I_NEXT:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[I_NEXT]] = call i32 @llvm.loop.decrement.reg.i32.i32.i32(i32 [[I]], i32 1)
; CHECK-NEXT: store i32 [[I]], i32* @A
; CHECK-NEXT: [[I2:%.*]] = mul i32 [[I]], [[I]]
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp sgt i32 [[I2]], 0
; CHECK-NEXT: br i1 [[EXITCOND]], label [[LOOP]], label [[LOOPEXIT:%.*]]
; CHECK: loopexit:
; CHECK-NEXT: ret i32 0
entry:
br label %loop
loop:
%i = phi i32 [ 10, %entry ], [ %i.next, %loop ]
%i.next = call i32 @llvm.loop.decrement.reg.i32.i32.i32(i32 %i, i32 1)
store i32 %i, i32* @A
%i2 = mul i32 %i, %i
%c = icmp sgt i32 %i2, 0
br i1 %c, label %loop, label %loopexit
loopexit:
ret i32 %i
}
@data = common global [240 x i8] zeroinitializer, align 16
@ -629,4 +657,5 @@ exit:
}
declare i32 @llvm.loop.decrement.reg.i32.i32.i32(i32, i32)

40
llvm/test/Transforms/LoopUnroll/ARM/dont-unroll-loopdec.ll Normal file
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@ -0,0 +1,40 @@
; RUN: opt -mtriple=thumbv8.1m.main -mattr=+mve.fp -loop-unroll --loop-unroll -S < %s | FileCheck %s
; CHECK-LABEL: foo
; CHECK: 5:
; CHECK: 6: ; preds = %6, %5
; CHECK: 15: ; preds = %6
; CHECK: br label %16
; CHECK: 16: ; preds = %15, %3
; CHECK: ret void
; CHECK: }
define void @foo(i8* nocapture, i8* nocapture readonly, i32) {
%4 = icmp sgt i32 %2, 0
br i1 %4, label %5, label %16
; <label>:5:
br label %6
; <label>:6:
%7 = phi i32 [ %13, %6 ], [ %2, %5 ]
%8 = phi i8* [ %10, %6 ], [ %1, %5 ]
%9 = phi i8* [ %12, %6 ], [ %0, %5 ]
%10 = getelementptr inbounds i8, i8* %8, i32 1
%11 = load i8, i8* %8, align 1
%12 = getelementptr inbounds i8, i8* %9, i32 1
store i8 %11, i8* %9, align 1
%13 = call i32 @llvm.loop.decrement.reg.i32.i32.i32(i32 %7, i32 1)
%14 = icmp sgt i32 %7, 1
br i1 %14, label %6, label %15
; <label>:15:
br label %16
; <label>:16:
ret void
}
declare i32 @llvm.loop.decrement.reg.i32.i32.i32(i32, i32)

28
llvm/unittests/Analysis/ScalarEvolutionTest.cpp
View File

@ -1683,6 +1683,34 @@ TEST_F(ScalarEvolutionsTest, SCEVExpanderShlNSW) {
"} ");
}
TEST_F(ScalarEvolutionsTest, SCEVLoopDecIntrinsic) {
LLVMContext C;
SMDiagnostic Err;
std::unique_ptr<Module> M = parseAssemblyString(
"define void @foo(i32 %N) { "
"entry: "
" %cmp3 = icmp sgt i32 %N, 0 "
" br i1 %cmp3, label %for.body, label %for.cond.cleanup "
"for.cond.cleanup: "
" ret void "
"for.body: "
" %i.04 = phi i32 [ %inc, %for.body ], [ 100, %entry ] "
" %inc = call i32 @llvm.loop.decrement.reg.i32.i32.i32(i32 %i.04, i32 1) "
" %exitcond = icmp ne i32 %inc, 0 "
" br i1 %exitcond, label %for.cond.cleanup, label %for.body "
"} "
"declare i32 @llvm.loop.decrement.reg.i32.i32.i32(i32, i32) ",
Err, C);
ASSERT_TRUE(M && "Could not parse module?");
ASSERT_TRUE(!verifyModule(*M) && "Must have been well formed!");
runWithSE(*M, "foo", [&](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
auto *ScevInc = SE.getSCEV(getInstructionByName(F, "inc"));
EXPECT_TRUE(isa<SCEVAddRecExpr>(ScevInc));
});
}
TEST_F(ScalarEvolutionsTest, SCEVComputeConstantDifference) {
LLVMContext C;
SMDiagnostic Err;