From 5eb6e29fcf32779d22cb5101e6e871f760493156 Mon Sep 17 00:00:00 2001 From: Kit Barton Date: Thu, 6 Aug 2015 19:01:57 +0000 Subject: [PATCH] Fix possible infinite loop in shrink wrapping when searching for save/restore points. There is an infinite loop that can occur in Shrink Wrapping while searching for the Save/Restore points. Part of this search checks whether the save/restore points are located in different loop nests and if so, uses the (post) dominator trees to find the immediate (post) dominator blocks. However, if the current block does not have any immediate (post) dominators then this search will result in an infinite loop. This can occur in code containing an infinite loop. The modification checks whether the immediate (post) dominator is different from the current save/restore block. If it is not, then the search terminates and the current location is not considered as a valid save/restore point for shrink wrapping. Phabricator: http://reviews.llvm.org/D11607 llvm-svn: 244247 --- lib/CodeGen/ShrinkWrap.cpp | 30 +++++++++++++++---- test/CodeGen/AArch64/arm64-shrink-wrapping.ll | 29 ++++++++++++++++++ test/CodeGen/ARM/arm-shrink-wrapping.ll | 28 +++++++++++++++++ test/CodeGen/X86/x86-shrink-wrapping.ll | 30 +++++++++++++++++++ 4 files changed, 111 insertions(+), 6 deletions(-) diff --git a/lib/CodeGen/ShrinkWrap.cpp b/lib/CodeGen/ShrinkWrap.cpp index f8ec1f358c4..261b8402bc0 100644 --- a/lib/CodeGen/ShrinkWrap.cpp +++ b/lib/CodeGen/ShrinkWrap.cpp @@ -309,12 +309,30 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB) { // Fix (C). if (Save && Restore && Save != Restore && MLI->getLoopFor(Save) != MLI->getLoopFor(Restore)) { - if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore)) - // Push Save outside of this loop. - Save = FindIDom<>(*Save, Save->predecessors(), *MDT); - else - // Push Restore outside of this loop. - Restore = FindIDom<>(*Restore, Restore->successors(), *MPDT); + if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore)) { + // Push Save outside of this loop if immediate dominator is different + // from save block. If immediate dominator is not different, bail out. + MachineBasicBlock *IDom = FindIDom<>(*Save, Save->predecessors(), *MDT); + if (IDom != Save) + Save = IDom; + else { + Save = nullptr; + break; + } + } + else { + // Push Restore outside of this loop if immediate post-dominator is + // different from restore block. If immediate post-dominator is not + // different, bail out. + MachineBasicBlock *IPdom = + FindIDom<>(*Restore, Restore->successors(), *MPDT); + if (IPdom != Restore) + Restore = IPdom; + else { + Restore = nullptr; + break; + } + } } } } diff --git a/test/CodeGen/AArch64/arm64-shrink-wrapping.ll b/test/CodeGen/AArch64/arm64-shrink-wrapping.ll index 599712be401..c547e8eceba 100644 --- a/test/CodeGen/AArch64/arm64-shrink-wrapping.ll +++ b/test/CodeGen/AArch64/arm64-shrink-wrapping.ll @@ -539,3 +539,32 @@ if.end: declare void @abort() #0 attributes #0 = { noreturn nounwind } + +; Make sure that we handle infinite loops properly When checking that the Save +; and Restore blocks are control flow equivalent, the loop searches for the +; immediate (post) dominator for the (restore) save blocks. When either the Save +; or Restore block is located in an infinite loop the only immediate (post) +; dominator is itself. In this case, we cannot perform shrink wrapping, but we +; should return gracefully and continue compilation. +; The only condition for this test is the compilation finishes correctly. +; +; CHECK-LABEL: infiniteloop +; CHECK: ret +define void @infiniteloop() { +entry: + br i1 undef, label %if.then, label %if.end + +if.then: + %ptr = alloca i32, i32 4 + br label %for.body + +for.body: ; preds = %for.body, %entry + %sum.03 = phi i32 [ 0, %if.then ], [ %add, %for.body ] + %call = tail call i32 bitcast (i32 (...)* @something to i32 ()*)() + %add = add nsw i32 %call, %sum.03 + store i32 %add, i32* %ptr + br label %for.body + +if.end: + ret void +} diff --git a/test/CodeGen/ARM/arm-shrink-wrapping.ll b/test/CodeGen/ARM/arm-shrink-wrapping.ll index f033ac47309..28ffca8344e 100644 --- a/test/CodeGen/ARM/arm-shrink-wrapping.ll +++ b/test/CodeGen/ARM/arm-shrink-wrapping.ll @@ -534,3 +534,31 @@ if.end: declare void @abort() #0 attributes #0 = { noreturn nounwind } + +; Make sure that we handle infinite loops properly When checking that the Save +; and Restore blocks are control flow equivalent, the loop searches for the +; immediate (post) dominator for the (restore) save blocks. When either the Save +; or Restore block is located in an infinite loop the only immediate (post) +; dominator is itself. In this case, we cannot perform shrink wrapping, but we +; should return gracefully and continue compilation. +; The only condition for this test is the compilation finishes correctly. +; CHECK-LABEL: infiniteloop +; CHECK: pop +define void @infiniteloop() { +entry: + br i1 undef, label %if.then, label %if.end + +if.then: + %ptr = alloca i32, i32 4 + br label %for.body + +for.body: ; preds = %for.body, %entry + %sum.03 = phi i32 [ 0, %if.then ], [ %add, %for.body ] + %call = tail call i32 asm sideeffect "mov $0, #1", "=r,~{r4}"() + %add = add nsw i32 %call, %sum.03 + store i32 %add, i32* %ptr + br label %for.body + +if.end: + ret void +} diff --git a/test/CodeGen/X86/x86-shrink-wrapping.ll b/test/CodeGen/X86/x86-shrink-wrapping.ll index 8c91335d91a..c6d20d5835d 100644 --- a/test/CodeGen/X86/x86-shrink-wrapping.ll +++ b/test/CodeGen/X86/x86-shrink-wrapping.ll @@ -637,3 +637,33 @@ if.end: declare void @abort() #0 attributes #0 = { noreturn nounwind } + + +; Make sure that we handle infinite loops properly When checking that the Save +; and Restore blocks are control flow equivalent, the loop searches for the +; immediate (post) dominator for the (restore) save blocks. When either the Save +; or Restore block is located in an infinite loop the only immediate (post) +; dominator is itself. In this case, we cannot perform shrink wrapping, but we +; should return gracefully and continue compilation. +; The only condition for this test is the compilation finishes correctly. +; +; CHECK-LABEL: infiniteloop +; CHECK: retq +define void @infiniteloop() { +entry: + br i1 undef, label %if.then, label %if.end + +if.then: + %ptr = alloca i32, i32 4 + br label %for.body + +for.body: ; preds = %for.body, %entry + %sum.03 = phi i32 [ 0, %if.then ], [ %add, %for.body ] + %call = tail call i32 asm "movl $$1, $0", "=r,~{ebx}"() + %add = add nsw i32 %call, %sum.03 + store i32 %add, i32* %ptr + br label %for.body + +if.end: + ret void +}