diff --git a/llvm/lib/CodeGen/PHIEliminationUtils.cpp b/llvm/lib/CodeGen/PHIEliminationUtils.cpp --- a/llvm/lib/CodeGen/PHIEliminationUtils.cpp +++ b/llvm/lib/CodeGen/PHIEliminationUtils.cpp @@ -27,31 +27,35 @@ // Usually, we just want to insert the copy before the first terminator // instruction. However, for the edge going to a landing pad, we must insert // the copy before the call/invoke instruction. Similarly for an INLINEASM_BR - // going to an indirect target. - if (!SuccMBB->isEHPad() && !SuccMBB->isInlineAsmBrIndirectTarget()) + // going to an indirect target. This is similar to SplitKit.cpp's + // computeLastInsertPoint, and similarly assumes that there cannot be multiple + // instructions that are Calls with EHPad successors or INLINEASM_BR in a + // block. + bool EHPadSuccessor = SuccMBB->isEHPad(); + if (!EHPadSuccessor && !SuccMBB->isInlineAsmBrIndirectTarget()) return MBB->getFirstTerminator(); - // Discover any defs/uses in this basic block. - SmallPtrSet DefUsesInMBB; + // Discover any defs in this basic block. + SmallPtrSet DefsInMBB; MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo(); - for (MachineInstr &RI : MRI.reg_instructions(SrcReg)) { + for (MachineInstr &RI : MRI.def_instructions(SrcReg)) if (RI.getParent() == MBB) - DefUsesInMBB.insert(&RI); - } + DefsInMBB.insert(&RI); - MachineBasicBlock::iterator InsertPoint; - if (DefUsesInMBB.empty()) { - // No defs. Insert the copy at the start of the basic block. - InsertPoint = MBB->begin(); - } else if (DefUsesInMBB.size() == 1) { - // Insert the copy immediately after the def/use. - InsertPoint = *DefUsesInMBB.begin(); - ++InsertPoint; - } else { - // Insert the copy immediately after the last def/use. - InsertPoint = MBB->end(); - while (!DefUsesInMBB.count(&*--InsertPoint)) {} - ++InsertPoint; + MachineBasicBlock::iterator InsertPoint = MBB->begin(); + // Insert the copy at the _latest_ point of: + // 1. Immediately AFTER the last def + // 2. Immediately BEFORE a call/inlineasm_br. + for (auto I = MBB->rbegin(), E = MBB->rend(); I != E; ++I) { + if (DefsInMBB.contains(&*I)) { + InsertPoint = std::next(I.getReverse()); + break; + } + if ((EHPadSuccessor && I->isCall()) || + I->getOpcode() == TargetOpcode::INLINEASM_BR) { + InsertPoint = I.getReverse(); + break; + } } // Make sure the copy goes after any phi nodes but before diff --git a/llvm/test/CodeGen/X86/callbr-asm-phi-placement.ll b/llvm/test/CodeGen/X86/callbr-asm-phi-placement.ll new file mode 100644 --- /dev/null +++ b/llvm/test/CodeGen/X86/callbr-asm-phi-placement.ll @@ -0,0 +1,44 @@ +; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py +; RUN: llc -mtriple=x86_64-unknown-linux-gnu -verify-machineinstrs -O2 < %s | FileCheck %s + +;; https://bugs.llvm.org/PR47468 + +;; PHI elimination should place copies BEFORE the inline asm, not +;; after, even if the inline-asm uses as an input the same value as +;; the PHI. + +declare void @foo(i8*) + +define void @test1(i8* %arg, i8** %mem) nounwind { +; CHECK-LABEL: test1: +; CHECK: # %bb.0: # %entry +; CHECK-NEXT: pushq %r14 +; CHECK-NEXT: pushq %rbx +; CHECK-NEXT: pushq %rax +; CHECK-NEXT: movq %rsi, %r14 +; CHECK-NEXT: .Ltmp0: # Block address taken +; CHECK-NEXT: .LBB0_1: # %loop +; CHECK-NEXT: # =>This Inner Loop Header: Depth=1 +; CHECK-NEXT: movq (%r14), %rbx +; CHECK-NEXT: callq foo +; CHECK-NEXT: movq %rbx, %rdi +; CHECK-NEXT: #APP +; CHECK-NEXT: #NO_APP +; CHECK-NEXT: # %bb.2: # %end +; CHECK-NEXT: addq $8, %rsp +; CHECK-NEXT: popq %rbx +; CHECK-NEXT: popq %r14 +; CHECK-NEXT: retq +entry: + br label %loop + +loop: + %a = phi i8* [ %arg, %entry ], [ %b, %loop ] + %b = load i8*, i8** %mem, align 8 + call void @foo(i8* %a) + callbr void asm sideeffect "", "*m,X"(i8* %b, i8* blockaddress(@test1, %loop)) + to label %end [label %loop] + +end: + ret void +}