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https://github.com/tinygo-org/tinygo.git
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compiler: use Tarjan's SCC algorithm to detect loops for defer
The compiler needs to know whether a defer is in a loop to determine whether to allocate stack or heap memory. Previously, this performed a DFS of the CFG every time a defer was found. This resulted in time complexity jointly proportional to the number of defers and the number of blocks in the function. Now, the compiler will instead use Tarjan's strongly connected components algorithm to find cycles in linear time. The search is performed lazily, so this has minimal performance impact on functions without defers. In order to implement Tarjan's SCC algorithm, additional state needed to be attached to the blocks. I chose to merge all of the per-block state into a single slice to simplify memory management.
This commit is contained in:
Nia Waldvogel
Ron Evans
+235
@@ -270,6 +270,241 @@ entry:
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ret void
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}
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; Function Attrs: nounwind
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define hidden void @main.deferInfiniteLoop(ptr %context) unnamed_addr #1 {
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entry:
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%deferPtr = alloca ptr, align 4
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store ptr null, ptr %deferPtr, align 4
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%deferframe.buf = alloca %runtime.deferFrame, align 4
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%0 = call ptr @llvm.stacksave.p0()
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call void @runtime.setupDeferFrame(ptr nonnull %deferframe.buf, ptr %0, ptr undef) #4
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br label %for.body
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for.body: ; preds = %for.body, %entry
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%defer.next = load ptr, ptr %deferPtr, align 4
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%defer.alloc.call = call dereferenceable(12) ptr @runtime.alloc(i32 12, ptr null, ptr undef) #4
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store i32 0, ptr %defer.alloc.call, align 4
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%defer.alloc.call.repack1 = getelementptr inbounds nuw i8, ptr %defer.alloc.call, i32 4
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store ptr %defer.next, ptr %defer.alloc.call.repack1, align 4
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%defer.alloc.call.repack3 = getelementptr inbounds nuw i8, ptr %defer.alloc.call, i32 8
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store i32 8, ptr %defer.alloc.call.repack3, align 4
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store ptr %defer.alloc.call, ptr %deferPtr, align 4
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br label %for.body
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recover: ; preds = %rundefers.end
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ret void
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lpad: ; No predecessors!
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br label %rundefers.loophead
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rundefers.loophead: ; preds = %rundefers.callback0, %lpad
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br i1 poison, label %rundefers.end, label %rundefers.loop
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rundefers.loop: ; preds = %rundefers.loophead
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switch i32 poison, label %rundefers.default [
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i32 0, label %rundefers.callback0
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]
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rundefers.callback0: ; preds = %rundefers.loop
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br label %rundefers.loophead
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rundefers.default: ; preds = %rundefers.loop
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unreachable
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rundefers.end: ; preds = %rundefers.loophead
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br label %recover
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}
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; Function Attrs: nounwind
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define hidden void @main.deferLoop(ptr %context) unnamed_addr #1 {
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entry:
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%deferPtr = alloca ptr, align 4
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store ptr null, ptr %deferPtr, align 4
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%deferframe.buf = alloca %runtime.deferFrame, align 4
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%0 = call ptr @llvm.stacksave.p0()
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call void @runtime.setupDeferFrame(ptr nonnull %deferframe.buf, ptr %0, ptr undef) #4
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br label %for.loop
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for.loop: ; preds = %for.body, %entry
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%1 = phi i32 [ 0, %entry ], [ %3, %for.body ]
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%2 = icmp slt i32 %1, 10
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br i1 %2, label %for.body, label %for.done
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for.body: ; preds = %for.loop
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%defer.next = load ptr, ptr %deferPtr, align 4
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%defer.alloc.call = call dereferenceable(12) ptr @runtime.alloc(i32 12, ptr null, ptr undef) #4
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store i32 0, ptr %defer.alloc.call, align 4
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%defer.alloc.call.repack13 = getelementptr inbounds nuw i8, ptr %defer.alloc.call, i32 4
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store ptr %defer.next, ptr %defer.alloc.call.repack13, align 4
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%defer.alloc.call.repack15 = getelementptr inbounds nuw i8, ptr %defer.alloc.call, i32 8
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store i32 %1, ptr %defer.alloc.call.repack15, align 4
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store ptr %defer.alloc.call, ptr %deferPtr, align 4
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%3 = add i32 %1, 1
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br label %for.loop
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for.done: ; preds = %for.loop
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br label %rundefers.block
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rundefers.after: ; preds = %rundefers.end
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call void @runtime.destroyDeferFrame(ptr nonnull %deferframe.buf, ptr undef) #4
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ret void
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rundefers.block: ; preds = %for.done
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br label %rundefers.loophead
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rundefers.loophead: ; preds = %rundefers.callback0, %rundefers.block
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%4 = load ptr, ptr %deferPtr, align 4
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%stackIsNil = icmp eq ptr %4, null
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br i1 %stackIsNil, label %rundefers.end, label %rundefers.loop
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rundefers.loop: ; preds = %rundefers.loophead
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%stack.next.gep = getelementptr inbounds nuw i8, ptr %4, i32 4
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%stack.next = load ptr, ptr %stack.next.gep, align 4
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store ptr %stack.next, ptr %deferPtr, align 4
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%callback = load i32, ptr %4, align 4
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switch i32 %callback, label %rundefers.default [
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i32 0, label %rundefers.callback0
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]
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rundefers.callback0: ; preds = %rundefers.loop
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%gep = getelementptr inbounds nuw i8, ptr %4, i32 8
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%param = load i32, ptr %gep, align 4
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call void @runtime.printlock(ptr undef) #4
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call void @runtime.printint32(i32 %param, ptr undef) #4
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call void @runtime.printunlock(ptr undef) #4
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br label %rundefers.loophead
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rundefers.default: ; preds = %rundefers.loop
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unreachable
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rundefers.end: ; preds = %rundefers.loophead
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br label %rundefers.after
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recover: ; preds = %rundefers.end1
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ret void
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lpad: ; No predecessors!
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br label %rundefers.loophead4
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rundefers.loophead4: ; preds = %rundefers.callback010, %lpad
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br i1 poison, label %rundefers.end1, label %rundefers.loop3
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rundefers.loop3: ; preds = %rundefers.loophead4
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switch i32 poison, label %rundefers.default2 [
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i32 0, label %rundefers.callback010
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]
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rundefers.callback010: ; preds = %rundefers.loop3
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br label %rundefers.loophead4
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rundefers.default2: ; preds = %rundefers.loop3
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unreachable
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rundefers.end1: ; preds = %rundefers.loophead4
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br label %recover
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}
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; Function Attrs: nounwind
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define hidden void @main.deferBetweenLoops(ptr %context) unnamed_addr #1 {
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entry:
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%defer.alloca = alloca { i32, ptr, i32 }, align 4
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%deferPtr = alloca ptr, align 4
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store ptr null, ptr %deferPtr, align 4
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%deferframe.buf = alloca %runtime.deferFrame, align 4
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%0 = call ptr @llvm.stacksave.p0()
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call void @runtime.setupDeferFrame(ptr nonnull %deferframe.buf, ptr %0, ptr undef) #4
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br label %for.loop
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for.loop: ; preds = %for.body, %entry
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%1 = phi i32 [ 0, %entry ], [ %3, %for.body ]
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%2 = icmp slt i32 %1, 10
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br i1 %2, label %for.body, label %for.done
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for.body: ; preds = %for.loop
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%3 = add i32 %1, 1
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br label %for.loop
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for.done: ; preds = %for.loop
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%defer.next = load ptr, ptr %deferPtr, align 4
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store i32 0, ptr %defer.alloca, align 4
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%defer.alloca.repack16 = getelementptr inbounds nuw i8, ptr %defer.alloca, i32 4
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store ptr %defer.next, ptr %defer.alloca.repack16, align 4
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%defer.alloca.repack18 = getelementptr inbounds nuw i8, ptr %defer.alloca, i32 8
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store i32 1, ptr %defer.alloca.repack18, align 4
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store ptr %defer.alloca, ptr %deferPtr, align 4
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br label %for.loop1
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for.loop1: ; preds = %for.body2, %for.done
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%4 = phi i32 [ 0, %for.done ], [ %6, %for.body2 ]
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%5 = icmp slt i32 %4, 10
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br i1 %5, label %for.body2, label %for.done3
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for.body2: ; preds = %for.loop1
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%6 = add i32 %4, 1
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br label %for.loop1
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for.done3: ; preds = %for.loop1
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br label %rundefers.block
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rundefers.after: ; preds = %rundefers.end
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call void @runtime.destroyDeferFrame(ptr nonnull %deferframe.buf, ptr undef) #4
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ret void
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rundefers.block: ; preds = %for.done3
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br label %rundefers.loophead
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rundefers.loophead: ; preds = %rundefers.callback0, %rundefers.block
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%7 = load ptr, ptr %deferPtr, align 4
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%stackIsNil = icmp eq ptr %7, null
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br i1 %stackIsNil, label %rundefers.end, label %rundefers.loop
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rundefers.loop: ; preds = %rundefers.loophead
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%stack.next.gep = getelementptr inbounds nuw i8, ptr %7, i32 4
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%stack.next = load ptr, ptr %stack.next.gep, align 4
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store ptr %stack.next, ptr %deferPtr, align 4
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%callback = load i32, ptr %7, align 4
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switch i32 %callback, label %rundefers.default [
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i32 0, label %rundefers.callback0
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]
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rundefers.callback0: ; preds = %rundefers.loop
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%gep = getelementptr inbounds nuw i8, ptr %7, i32 8
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%param = load i32, ptr %gep, align 4
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call void @runtime.printlock(ptr undef) #4
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call void @runtime.printint32(i32 %param, ptr undef) #4
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call void @runtime.printunlock(ptr undef) #4
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br label %rundefers.loophead
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rundefers.default: ; preds = %rundefers.loop
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unreachable
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rundefers.end: ; preds = %rundefers.loophead
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br label %rundefers.after
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recover: ; preds = %rundefers.end4
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ret void
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lpad: ; No predecessors!
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br label %rundefers.loophead7
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rundefers.loophead7: ; preds = %rundefers.callback013, %lpad
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br i1 poison, label %rundefers.end4, label %rundefers.loop6
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rundefers.loop6: ; preds = %rundefers.loophead7
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switch i32 poison, label %rundefers.default5 [
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i32 0, label %rundefers.callback013
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]
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rundefers.callback013: ; preds = %rundefers.loop6
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br label %rundefers.loophead7
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rundefers.default5: ; preds = %rundefers.loop6
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unreachable
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rundefers.end4: ; preds = %rundefers.loophead7
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br label %recover
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}
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attributes #0 = { allockind("alloc,zeroed") allocsize(0) "alloc-family"="runtime.alloc" "target-features"="+armv7-m,+hwdiv,+soft-float,+thumb-mode,-aes,-bf16,-cdecp0,-cdecp1,-cdecp2,-cdecp3,-cdecp4,-cdecp5,-cdecp6,-cdecp7,-crc,-crypto,-d32,-dotprod,-dsp,-fp-armv8,-fp-armv8d16,-fp-armv8d16sp,-fp-armv8sp,-fp16,-fp16fml,-fp64,-fpregs,-fullfp16,-hwdiv-arm,-i8mm,-lob,-mve,-mve.fp,-neon,-pacbti,-ras,-sb,-sha2,-vfp2,-vfp2sp,-vfp3,-vfp3d16,-vfp3d16sp,-vfp3sp,-vfp4,-vfp4d16,-vfp4d16sp,-vfp4sp" }
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attributes #1 = { nounwind "target-features"="+armv7-m,+hwdiv,+soft-float,+thumb-mode,-aes,-bf16,-cdecp0,-cdecp1,-cdecp2,-cdecp3,-cdecp4,-cdecp5,-cdecp6,-cdecp7,-crc,-crypto,-d32,-dotprod,-dsp,-fp-armv8,-fp-armv8d16,-fp-armv8d16sp,-fp-armv8sp,-fp16,-fp16fml,-fp64,-fpregs,-fullfp16,-hwdiv-arm,-i8mm,-lob,-mve,-mve.fp,-neon,-pacbti,-ras,-sb,-sha2,-vfp2,-vfp2sp,-vfp3,-vfp3d16,-vfp3d16sp,-vfp3sp,-vfp4,-vfp4d16,-vfp4d16sp,-vfp4sp" }
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attributes #2 = { "target-features"="+armv7-m,+hwdiv,+soft-float,+thumb-mode,-aes,-bf16,-cdecp0,-cdecp1,-cdecp2,-cdecp3,-cdecp4,-cdecp5,-cdecp6,-cdecp7,-crc,-crypto,-d32,-dotprod,-dsp,-fp-armv8,-fp-armv8d16,-fp-armv8d16sp,-fp-armv8sp,-fp16,-fp16fml,-fp64,-fpregs,-fullfp16,-hwdiv-arm,-i8mm,-lob,-mve,-mve.fp,-neon,-pacbti,-ras,-sb,-sha2,-vfp2,-vfp2sp,-vfp3,-vfp3d16,-vfp3d16sp,-vfp3sp,-vfp4,-vfp4d16,-vfp4d16sp,-vfp4sp" }
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Vendored
+20
@@ -18,3 +18,23 @@ func deferMultiple() {
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}()
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external()
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}
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func deferInfiniteLoop() {
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for {
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defer print(8)
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}
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}
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func deferLoop() {
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for i := 0; i < 10; i++ {
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defer print(i)
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}
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}
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func deferBetweenLoops() {
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for i := 0; i < 10; i++ {
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}
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defer print(1)
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for i := 0; i < 10; i++ {
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}
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}
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