From fe3275edf336d190b15660ae39e15fe3a70715c7 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Mon, 15 Jul 2019 21:16:29 +0000 Subject: [PATCH] [LoopUnroll+LoopUnswitch] do not transform loops containing callbr Summary: There is currently a correctness issue when unrolling loops containing callbr's where their indirect targets are being updated correctly to the newly created labels, but their operands are not. This manifests in unrolled loops where the second and subsequent copies of callbr instructions have blockaddresses of the label from the first instance of the unrolled loop, which would result in nonsensical runtime control flow. For now, conservatively do not unroll the loop. In the future, I think we can pursue unrolling such loops provided we transform the cloned callbr's operands correctly. Such a transform and its legalities are being discussed in: https://reviews.llvm.org/D64101 Link: https://bugs.llvm.org/show_bug.cgi?id=42489 Link: https://groups.google.com/forum/#!topic/clang-built-linux/z-hRWP9KqPI Reviewers: fhahn, hfinkel, efriedma Reviewed By: fhahn, hfinkel, efriedma Subscribers: efriedma, hiraditya, zzheng, dmgreen, llvm-commits, pirama, kees, nathanchance, E5ten, craig.topper, chandlerc, glider, void, srhines Tags: #llvm Differential Revision: https://reviews.llvm.org/D64368 llvm-svn: 366130 --- lib/Analysis/LoopInfo.cpp | 5 +- test/Transforms/LoopUnroll/callbr.ll | 51 ++++++++++++++++++++ test/Transforms/LoopUnswitch/callbr.ll | 66 ++++++++++++++++++++++++++ 3 files changed, 121 insertions(+), 1 deletion(-) create mode 100644 test/Transforms/LoopUnroll/callbr.ll create mode 100644 test/Transforms/LoopUnswitch/callbr.ll diff --git a/lib/Analysis/LoopInfo.cpp b/lib/Analysis/LoopInfo.cpp index 00dbe30c2b3..c59e48a7a98 100644 --- a/lib/Analysis/LoopInfo.cpp +++ b/lib/Analysis/LoopInfo.cpp @@ -432,8 +432,11 @@ bool Loop::isLoopSimplifyForm() const { bool Loop::isSafeToClone() const { // Return false if any loop blocks contain indirectbrs, or there are any calls // to noduplicate functions. + // FIXME: it should be ok to clone CallBrInst's if we correctly update the + // operand list to reflect the newly cloned labels. for (BasicBlock *BB : this->blocks()) { - if (isa(BB->getTerminator())) + if (isa(BB->getTerminator()) || + isa(BB->getTerminator())) return false; for (Instruction &I : *BB) diff --git a/test/Transforms/LoopUnroll/callbr.ll b/test/Transforms/LoopUnroll/callbr.ll new file mode 100644 index 00000000000..22206b46662 --- /dev/null +++ b/test/Transforms/LoopUnroll/callbr.ll @@ -0,0 +1,51 @@ +; RUN: opt -loop-unroll -S %s | FileCheck %s + +; Check that the loop body exists. +; CHECK: for.body +; CHECK: if.then +; CHECK: asm.fallthrough +; CHECK: l_yes +; CHECK: for.inc + +; Check that the loop body does not get unrolled. We could modify this test in +; the future to support loop unrolling callbr's IFF we checked that the callbr +; operands were unrolled/updated correctly, as today they are not. +; CHECK-NOT: if.then.1 +; CHECK-NOT: asm.fallthrough.1 +; CHECK-NOT: l_yes.1 +; CHECK-NOT: for.inc.1 +; CHECK-NOT: if.then.2 +; CHECK-NOT: asm.fallthrough.2 +; CHECK-NOT: l_yes.2 +; CHECK-NOT: for.inc.2 + +define dso_local void @d() { +entry: + br label %for.body + +for.cond.cleanup: ; preds = %for.inc + ret void + +for.body: ; preds = %for.inc, %entry + %e.04 = phi i32 [ 0, %entry ], [ %inc, %for.inc ] + %tobool = icmp eq i32 %e.04, 0 + br i1 %tobool, label %for.inc, label %if.then + +if.then: ; preds = %for.body + callbr void asm sideeffect "1: nop\0A\09.quad b, ${0:l}, $$5\0A\09", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@d, %l_yes)) + to label %asm.fallthrough [label %l_yes] + +asm.fallthrough: ; preds = %if.then + br label %l_yes + +l_yes: ; preds = %asm.fallthrough, %if.then + %call = tail call i32 (...) @g() + br label %for.inc + +for.inc: ; preds = %for.body, %l_yes + %inc = add nuw nsw i32 %e.04, 1 + %exitcond = icmp eq i32 %inc, 3 + br i1 %exitcond, label %for.cond.cleanup, label %for.body +} + +declare dso_local i32 @g(...) local_unnamed_addr diff --git a/test/Transforms/LoopUnswitch/callbr.ll b/test/Transforms/LoopUnswitch/callbr.ll new file mode 100644 index 00000000000..6e05374d329 --- /dev/null +++ b/test/Transforms/LoopUnswitch/callbr.ll @@ -0,0 +1,66 @@ +; RUN: opt -loop-unswitch %s -S | FileCheck %s + +; We want to check that the loop does not get split (so only 2 callbr's not 4). +; It's ok to modify this test in the future should we allow the loop containing +; callbr to be unswitched and are able to do so correctly. + +; CHECK: callbr void asm sideeffect "# ${0:l}", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %10)) +; CHECK: to label %7 [label %10] +; CHECK: callbr void asm sideeffect "# ${0:l}", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %10)) +; CHECK: to label %9 [label %10] + +; CHECK-NOT: callbr void asm sideeffect "# ${0:l}", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %10)) +; CHECK-NOT: to label %7 [label %10] +; CHECK-NOT: callbr void asm sideeffect "# ${0:l}", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %10)) +; CHECK-NOT: to label %9 [label %10] +; CHECK-NOT: callbr void asm sideeffect "# ${0:l}", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %19)) +; CHECK-NOT: to label %16 [label %19] +; CHECK-NOT: callbr void asm sideeffect "# ${0:l}", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %19)) +; CHECK-NOT: to label %18 [label %19] + +; This test is essentially: +; void foo(int n) { +; for (int i = 0; i < 1000; ++i) +; if (n) { +; asm goto("# %l0"::::bar); +; bar:; +; } else { +; asm goto("# %l0"::::baz); +; baz:; +; } +;} + +define dso_local void @foo(i32) #0 { + br label %2 + +2: ; preds = %10, %1 + %.0 = phi i32 [ 0, %1 ], [ %11, %10 ] + %3 = icmp ult i32 %.0, 1000 + br i1 %3, label %4, label %12 + +4: ; preds = %2 + %5 = icmp eq i32 %0, 0 + br i1 %5, label %8, label %6 + +6: ; preds = %4 + callbr void asm sideeffect "# ${0:l}", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %10)) #0 + to label %7 [label %10] + +7: ; preds = %6 + br label %10 + +8: ; preds = %4 + callbr void asm sideeffect "# ${0:l}", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %10)) #0 + to label %9 [label %10] + +9: ; preds = %8 + br label %10 + +10: ; preds = %7, %6, %9, %8 + %11 = add nuw nsw i32 %.0, 1 + br label %2 + +12: ; preds = %2 + ret void +} +