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[EarlyCSE] Simplify guard intrinsics
Summary: This change teaches EarlyCSE some basic properties of guard intrinsics: - Guard intrinsics read all memory, but don't write to any memory - After a guard has executed, the condition it was guarding on can be assumed to be true - Guard intrinsics on a constant `true` are no-ops Reviewers: reames, hfinkel Subscribers: mcrosier, llvm-commits Differential Revision: http://reviews.llvm.org/D19578 llvm-svn: 268120
This commit is contained in:
Sanjoy Das
parent
701c21ea10
commit
ee81b23fe7
@ -554,6 +554,29 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
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continue;
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}
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if (match(Inst, m_Intrinsic<Intrinsic::experimental_guard>())) {
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Value *Cond = cast<CallInst>(Inst)->getArgOperand(0);
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if (match(Cond, m_One())) {
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// Elide guards on true, since operationally they're no-ops. In the
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// future we can consider more sophisticated tradeoffs here with
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// consideration to potential for check widening, but for now we keep
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// things simple.
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Inst->eraseFromParent();
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} else if (auto *CondI = dyn_cast<Instruction>(Cond)) {
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// The condition we're on guarding here is true for all dominated
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// locations.
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if (SimpleValue::canHandle(CondI))
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AvailableValues.insert(CondI, ConstantInt::getTrue(BB->getContext()));
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}
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// Guard intrinsics read all memory, but don't write any memory.
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// Accordingly, don't update the generation but consume the last store (to
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// avoid an incorrect DSE).
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LastStore = nullptr;
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continue;
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}
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// If the instruction can be simplified (e.g. X+0 = X) then replace it with
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// its simpler value.
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if (Value *V = SimplifyInstruction(Inst, DL, &TLI, &DT, &AC)) {
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181
llvm/test/Transforms/EarlyCSE/guards.ll
Normal file
181
llvm/test/Transforms/EarlyCSE/guards.ll
Normal file
@ -0,0 +1,181 @@
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; RUN: opt -S -early-cse < %s | FileCheck %s
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declare void @llvm.experimental.guard(i1,...)
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define i32 @test0(i32* %ptr, i1 %cond) {
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; We can do store to load forwarding over a guard, since it does not
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; clobber memory
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; CHECK-LABEL: @test0(
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; CHECK-NEXT: store i32 40, i32* %ptr
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ]
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; CHECK-NEXT: ret i32 40
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store i32 40, i32* %ptr
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call void(i1,...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ]
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%rval = load i32, i32* %ptr
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ret i32 %rval
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}
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define i32 @test1(i32* %val, i1 %cond) {
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; We can CSE loads over a guard, since it does not clobber memory
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; CHECK-LABEL: @test1(
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; CHECK-NEXT: %val0 = load i32, i32* %val
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ]
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; CHECK-NEXT: ret i32 0
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%val0 = load i32, i32* %val
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call void(i1,...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ]
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%val1 = load i32, i32* %val
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%rval = sub i32 %val0, %val1
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ret i32 %rval
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}
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define i32 @test2() {
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; Guards on "true" get removed
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; CHECK-LABEL: @test2(
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; CHECK-NEXT: ret i32 0
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call void(i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
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ret i32 0
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}
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define i32 @test3(i32 %val) {
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; After a guard has executed the condition it was guarding is known to
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; be true.
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; CHECK-LABEL: @test3(
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; CHECK-NEXT: %cond0 = icmp slt i32 %val, 40
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %cond0) [ "deopt"() ]
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; CHECK-NEXT: ret i32 -1
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%cond0 = icmp slt i32 %val, 40
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call void(i1,...) @llvm.experimental.guard(i1 %cond0) [ "deopt"() ]
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%cond1 = icmp slt i32 %val, 40
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call void(i1,...) @llvm.experimental.guard(i1 %cond1) [ "deopt"() ]
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%cond2 = icmp slt i32 %val, 40
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%rval = sext i1 %cond2 to i32
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ret i32 %rval
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}
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define i32 @test3.unhandled(i32 %val) {
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; After a guard has executed the condition it was guarding is known to
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; be true.
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; CHECK-LABEL: @test3.unhandled(
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; CHECK-NEXT: %cond0 = icmp slt i32 %val, 40
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %cond0) [ "deopt"() ]
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; CHECK-NEXT: %cond1 = icmp sge i32 %val, 40
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %cond1) [ "deopt"() ]
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; CHECK-NEXT: ret i32 0
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; Demonstrates a case we do not yet handle (it is legal to fold %cond2
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; to false)
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%cond0 = icmp slt i32 %val, 40
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call void(i1,...) @llvm.experimental.guard(i1 %cond0) [ "deopt"() ]
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%cond1 = icmp sge i32 %val, 40
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call void(i1,...) @llvm.experimental.guard(i1 %cond1) [ "deopt"() ]
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ret i32 0
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}
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define i32 @test4(i32 %val, i1 %c) {
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; Same as test3, but with some control flow involved.
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; CHECK-LABEL: @test4(
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; CHECK: entry:
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; CHECK-NEXT: %cond0 = icmp slt i32 %val, 40
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %cond0
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; CHECK-NEXT: br label %bb0
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; CHECK: bb0:
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; CHECK-NEXT: %cond2 = icmp ult i32 %val, 200
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %cond2
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; CHECK-NEXT: br i1 %c, label %left, label %right
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; CHECK: left:
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; CHECK-NEXT: ret i32 0
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; CHECK: right:
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; CHECK-NEXT: ret i32 20
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entry:
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%cond0 = icmp slt i32 %val, 40
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call void(i1,...) @llvm.experimental.guard(i1 %cond0) [ "deopt"() ]
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%cond1 = icmp slt i32 %val, 40
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call void(i1,...) @llvm.experimental.guard(i1 %cond1) [ "deopt"() ]
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br label %bb0
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bb0:
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%cond2 = icmp ult i32 %val, 200
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call void(i1,...) @llvm.experimental.guard(i1 %cond2) [ "deopt"() ]
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br i1 %c, label %left, label %right
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left:
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%cond3 = icmp ult i32 %val, 200
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call void(i1,...) @llvm.experimental.guard(i1 %cond3) [ "deopt"() ]
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ret i32 0
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right:
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ret i32 20
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}
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define i32 @test5(i32 %val, i1 %c) {
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; Same as test4, but the %left block has mutliple predecessors.
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; CHECK-LABEL: @test5(
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; CHECK: entry:
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; CHECK-NEXT: %cond0 = icmp slt i32 %val, 40
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %cond0
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; CHECK-NEXT: br label %bb0
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; CHECK: bb0:
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; CHECK-NEXT: %cond2 = icmp ult i32 %val, 200
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %cond2
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; CHECK-NEXT: br i1 %c, label %left, label %right
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; CHECK: left:
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; CHECK-NEXT: br label %right
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; CHECK: right:
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; CHECK-NEXT: br label %left
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entry:
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%cond0 = icmp slt i32 %val, 40
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call void(i1,...) @llvm.experimental.guard(i1 %cond0) [ "deopt"() ]
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%cond1 = icmp slt i32 %val, 40
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call void(i1,...) @llvm.experimental.guard(i1 %cond1) [ "deopt"() ]
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br label %bb0
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bb0:
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%cond2 = icmp ult i32 %val, 200
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call void(i1,...) @llvm.experimental.guard(i1 %cond2) [ "deopt"() ]
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br i1 %c, label %left, label %right
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left:
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%cond3 = icmp ult i32 %val, 200
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call void(i1,...) @llvm.experimental.guard(i1 %cond3) [ "deopt"() ]
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br label %right
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right:
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br label %left
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}
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define void @test6(i1 %c, i32* %ptr) {
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; Check that we do not DSE over calls to @llvm.experimental.guard.
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; Guard intrinsics do _read_ memory, so th call to guard below needs
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; to see the store of 500 to %ptr
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; CHECK-LABEL: @test6(
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; CHECK-NEXT: store i32 500, i32* %ptr
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %c) [ "deopt"() ]
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; CHECK-NEXT: store i32 600, i32* %ptr
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store i32 500, i32* %ptr
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call void(i1,...) @llvm.experimental.guard(i1 %c) [ "deopt"() ]
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store i32 600, i32* %ptr
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ret void
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}
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