| commit 13a97305ba77f44eccba16087320c8aa016ac6da |
| Author: Fangrui Song <maskray@google.com> |
| Date: Mon Feb 17 17:43:09 2020 -0800 |
| |
| [JumpThreading] Skip unconditional PredBB when threading jumps through two basic blocks |
| |
| Fixes https://bugs.llvm.org/show_bug.cgi?id=44922 (caused by 4698bf145d583e26ed438026ef7fde031ef322b1) |
| |
| ThreadThroughTwoBasicBlocks assumes PredBBBranch is conditional. The following code can segfault. |
| |
| AddPHINodeEntriesForMappedBlock(PredBBBranch->getSuccessor(1), PredBB, NewBB, |
| ValueMapping); |
| |
| We can also allow unconditional PredBB, but the produced code is not |
| better. |
| |
| Reviewed By: kazu |
| |
| Differential Revision: https://reviews.llvm.org/D74747 |
| |
| diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp |
| index 411e3c1cca2..616d64a794b 100644 |
| --- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp |
| +++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp |
| @@ -2113,11 +2113,11 @@ bool JumpThreadingPass::MaybeThreadThroughTwoBasicBlocks(BasicBlock *BB, |
| if (!PredBB) |
| return false; |
| |
| - // Require that PredBB end with a Branch. If PredBB ends with an |
| - // unconditional branch, we should be merging PredBB and BB instead. For |
| + // Require that PredBB end with a conditional Branch. If PredBB ends with an |
| + // unconditional branch, we should be merging PredBB and BB instead. For |
| // simplicity, we don't deal with a switch. |
| BranchInst *PredBBBranch = dyn_cast<BranchInst>(PredBB->getTerminator()); |
| - if (!PredBBBranch) |
| + if (!PredBBBranch || PredBBBranch->isUnconditional()) |
| return false; |
| |
| // If PredBB has exactly one incoming edge, we don't gain anything by copying |
| diff --git a/llvm/test/Transforms/JumpThreading/thread-two-bbs6.ll b/llvm/test/Transforms/JumpThreading/thread-two-bbs6.ll |
| new file mode 100644 |
| index 00000000000..0d8d2f058b8 |
| --- /dev/null |
| +++ b/llvm/test/Transforms/JumpThreading/thread-two-bbs6.ll |
| @@ -0,0 +1,42 @@ |
| +;; Test that we skip unconditional PredBB when threading jumps through two |
| +;; successive basic blocks. |
| +; RUN: opt -S -passes='function(jump-threading)' < %s | FileCheck %s |
| + |
| +target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" |
| +target triple = "x86_64-unknown-linux-gnu" |
| + |
| +define i32 @f(i32* %0) { |
| +; CHECK-LABEL: @f |
| +; CHECK: br i1 %good, label %pred.bb, label %pred.pred.bb |
| +entry: |
| + %size = call i64 @get_size(i32* %0) |
| + %good = icmp ugt i64 %size, 3 |
| + br i1 %good, label %pred.bb, label %pred.pred.bb |
| + |
| +; CHECK: pred.pred.bb: |
| +; CHECK: br label %pred.bb |
| +; CHECK: pred.bb: |
| +; CHECK: br label %bb |
| +; CHECK: bb: |
| +pred.pred.bb: ; preds = %entry |
| + call void @effect() |
| + br label %pred.bb |
| +pred.bb: ; preds = %pred.pred.bb, %entry |
| + %v = load i32, i32* %0 |
| + br label %bb |
| + |
| +bb: ; preds = %pred.bb |
| + call void @effect1(i8* blockaddress(@f, %bb)) |
| + br i1 %good, label %cont2, label %cont1 |
| + |
| +cont1: ; preds = %bb |
| + br i1 %good, label %exit, label %cont2 |
| +cont2: ; preds = %bb |
| + br label %exit |
| +exit: ; preds = %cont1, %cont2 |
| + ret i32 %v |
| +} |
| + |
| +declare i64 @get_size(i32*) |
| +declare void @effect() |
| +declare void @effect1(i8*) |
