From ed2ca70ccff2e2654a41d6d9fc74683d6ec0a2ff Mon Sep 17 00:00:00 2001 From: Ekaterina Romanova Date: Thu, 13 Mar 2014 18:47:12 +0000 Subject: [PATCH] Fix for http://llvm.org/bugs/show_bug.cgi?id=18590 This patch fixes the bug in peephole optimization that folds a load which defines one vreg into the one and only use of that vreg. With debug info, a DBG_VALUE that referenced the vreg considered to be a use, preventing the optimization. The fix is to ignore DBG_VALUE's during the optimization, and undef a DBG_VALUE that references a vreg that gets removed. Patch by Trevor Smigiel! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203829 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/llvm/CodeGen/MachineRegisterInfo.h | 4 ++ lib/CodeGen/DeadMachineInstructionElim.cpp | 12 +--- lib/CodeGen/MachineRegisterInfo.cpp | 15 ++++ lib/CodeGen/PeepholeOptimizer.cpp | 14 +++- test/CodeGen/X86/dbg-changes-codegen.ll | 83 ++++++++++++++++++++++ 5 files changed, 114 insertions(+), 14 deletions(-) create mode 100644 test/CodeGen/X86/dbg-changes-codegen.ll diff --git a/include/llvm/CodeGen/MachineRegisterInfo.h b/include/llvm/CodeGen/MachineRegisterInfo.h index ecaaf0a0689..01fa00fe241 100644 --- a/include/llvm/CodeGen/MachineRegisterInfo.h +++ b/include/llvm/CodeGen/MachineRegisterInfo.h @@ -510,6 +510,10 @@ public: return Hint.first ? 0 : Hint.second; } + /// markUsesInDebugValueAsUndef - Mark every DBG_VALUE referencing the + /// specified register as undefined which causes the DBG_VALUE to be + /// deleted during LiveDebugVariables analysis. + void markUsesInDebugValueAsUndef(unsigned Reg) const; //===--------------------------------------------------------------------===// // Physical Register Use Info diff --git a/lib/CodeGen/DeadMachineInstructionElim.cpp b/lib/CodeGen/DeadMachineInstructionElim.cpp index bbb4da83305..643efc2a4f9 100644 --- a/lib/CodeGen/DeadMachineInstructionElim.cpp +++ b/lib/CodeGen/DeadMachineInstructionElim.cpp @@ -127,17 +127,7 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) { unsigned Reg = MO.getReg(); if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue; - MachineRegisterInfo::use_iterator nextI; - for (MachineRegisterInfo::use_iterator I = MRI->use_begin(Reg), - E = MRI->use_end(); I!=E; I=nextI) { - nextI = std::next(I); // I is invalidated by the setReg - MachineOperand& Use = I.getOperand(); - MachineInstr *UseMI = Use.getParent(); - if (UseMI==MI) - continue; - assert(Use.isDebug()); - UseMI->getOperand(0).setReg(0U); - } + MRI->markUsesInDebugValueAsUndef(Reg); } AnyChanges = true; MI->eraseFromParent(); diff --git a/lib/CodeGen/MachineRegisterInfo.cpp b/lib/CodeGen/MachineRegisterInfo.cpp index 4029f4a2bbc..3dabcbed7fc 100644 --- a/lib/CodeGen/MachineRegisterInfo.cpp +++ b/lib/CodeGen/MachineRegisterInfo.cpp @@ -414,3 +414,18 @@ bool MachineRegisterInfo::isConstantPhysReg(unsigned PhysReg, return false; return true; } + +/// markUsesInDebugValueAsUndef - Mark every DBG_VALUE referencing the +/// specified register as undefined which causes the DBG_VALUE to be +/// deleted during LiveDebugVariables analysis. +void MachineRegisterInfo::markUsesInDebugValueAsUndef(unsigned Reg) const { + // Mark any DBG_VALUE that uses Reg as undef (but don't delete it.) + MachineRegisterInfo::use_iterator nextI; + for (use_iterator I = use_begin(Reg), E = use_end(); I != E; I = nextI) { + nextI = std::next(I); // I is invalidated by the setReg + MachineOperand& Use = I.getOperand(); + MachineInstr *UseMI = Use.getParent(); + if (UseMI->isDebugValue()) + UseMI->getOperand(0).setReg(0U); + } +} diff --git a/lib/CodeGen/PeepholeOptimizer.cpp b/lib/CodeGen/PeepholeOptimizer.cpp index 18af9d480c7..8bf2270755e 100644 --- a/lib/CodeGen/PeepholeOptimizer.cpp +++ b/lib/CodeGen/PeepholeOptimizer.cpp @@ -505,12 +505,12 @@ bool PeepholeOptimizer::isLoadFoldable(MachineInstr *MI, return false; unsigned Reg = MI->getOperand(0).getReg(); - // To reduce compilation time, we check MRI->hasOneUse when inserting + // To reduce compilation time, we check MRI->hasOneNonDBGUse when inserting // loads. It should be checked when processing uses of the load, since // uses can be removed during peephole. if (!MI->getOperand(0).getSubReg() && TargetRegisterInfo::isVirtualRegister(Reg) && - MRI->hasOneUse(Reg)) { + MRI->hasOneNonDBGUse(Reg)) { FoldAsLoadDefReg = Reg; return true; } @@ -594,10 +594,14 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) { ++MII; LocalMIs.insert(MI); + // Skip debug values. They should not affect this peephole optimization. + if (MI->isDebugValue()) + continue; + // If there exists an instruction which belongs to the following // categories, we will discard the load candidate. if (MI->isPosition() || MI->isPHI() || MI->isImplicitDef() || - MI->isKill() || MI->isInlineAsm() || MI->isDebugValue() || + MI->isKill() || MI->isInlineAsm() || MI->hasUnmodeledSideEffects()) { FoldAsLoadDefReg = 0; continue; @@ -633,6 +637,9 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) { if (!isLoadFoldable(MI, FoldAsLoadDefReg) && FoldAsLoadDefReg) { // We need to fold load after optimizeCmpInstr, since optimizeCmpInstr // can enable folding by converting SUB to CMP. + // Save FoldAsLoadDefReg because optimizeLoadInstr() resets it and we + // need it for markUsesInDebugValueAsUndef(). + unsigned FoldedReg = FoldAsLoadDefReg; MachineInstr *DefMI = 0; MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI, FoldAsLoadDefReg, DefMI); @@ -645,6 +652,7 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) { LocalMIs.insert(FoldMI); MI->eraseFromParent(); DefMI->eraseFromParent(); + MRI->markUsesInDebugValueAsUndef(FoldedReg); ++NumLoadFold; // MI is replaced with FoldMI. diff --git a/test/CodeGen/X86/dbg-changes-codegen.ll b/test/CodeGen/X86/dbg-changes-codegen.ll new file mode 100644 index 00000000000..7cf94ee0f1e --- /dev/null +++ b/test/CodeGen/X86/dbg-changes-codegen.ll @@ -0,0 +1,83 @@ +; RUN: llc < %s -march=x86-64 | FileCheck %s + +; The Peephole optimizer should fold the load into the cmp even with debug info. +; CHECK-LABEL: _ZN3Foo3batEv +; CHECK-NOT: movq pfoo +; CHECK: cmpq {{%[a-z]+}}, pfoo(%rip) +; +; CHECK-LABEL: _Z3bazv +; CHECK-NOT: movq wibble2 +; CHECK: cmpq {{%[a-z]+}}, wibble2(%rip) + +; Regenerate test with this command: +; clang -emit-llvm -S -O2 -g +; from this source: +; struct Foo { +; bool bat(); +; bool operator==(Foo &arg) { return (this == &arg); } +; }; +; Foo *pfoo; +; bool Foo::bat() { return (*this == *pfoo); } +; +; struct Wibble { +; int x; +; } *wibble1, *wibble2; +; struct Flibble { +; void bar(Wibble *c) { +; if (c < wibble2) +; wibble2 = 0; +; c->x = 0; +; } +; } flibble; +; void baz() { flibble.bar(wibble1); } + +%struct.Foo = type { i8 } +%struct.Wibble = type { i32 } +%struct.Flibble = type { i8 } + +@pfoo = global %struct.Foo* null, align 8 +@wibble1 = global %struct.Wibble* null, align 8 +@wibble2 = global %struct.Wibble* null, align 8 +@flibble = global %struct.Flibble zeroinitializer, align 1 + +; Function Attrs: nounwind readonly uwtable +define zeroext i1 @_ZN3Foo3batEv(%struct.Foo* %this) #0 align 2 { +entry: + %0 = load %struct.Foo** @pfoo, align 8 + tail call void @llvm.dbg.value(metadata !{%struct.Foo* %0}, i64 0, metadata !62) + %cmp.i = icmp eq %struct.Foo* %0, %this + ret i1 %cmp.i +} + +; Function Attrs: nounwind uwtable +define void @_Z3bazv() #1 { +entry: + %0 = load %struct.Wibble** @wibble1, align 8 + tail call void @llvm.dbg.value(metadata !64, i64 0, metadata !65) + %1 = load %struct.Wibble** @wibble2, align 8 + %cmp.i = icmp ugt %struct.Wibble* %1, %0 + br i1 %cmp.i, label %if.then.i, label %_ZN7Flibble3barEP6Wibble.exit + +if.then.i: ; preds = %entry + store %struct.Wibble* null, %struct.Wibble** @wibble2, align 8 + br label %_ZN7Flibble3barEP6Wibble.exit + +_ZN7Flibble3barEP6Wibble.exit: ; preds = %entry, %if.then.i + %x.i = getelementptr inbounds %struct.Wibble* %0, i64 0, i32 0 + store i32 0, i32* %x.i, align 4 + ret void +} + +; Function Attrs: nounwind readnone +declare void @llvm.dbg.value(metadata, i64, metadata) #2 + +attributes #0 = { nounwind readonly uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-frame-pointer-elim-non-leaf"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "unsafe-fp-math"="false" "use-soft-float"="false" } +attributes #1 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-frame-pointer-elim-non-leaf"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "unsafe-fp-math"="false" "use-soft-float"="false" } +attributes #2 = { nounwind readnone } + + +!17 = metadata !{i32 786448, null, null, null, i32 0, i64 0, i64 0, i64 0, i32 0, null} ; [ DW_TAG_reference_type ] [line 0, size 0, align 0, offset 0] [from Foo] +!45 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, null} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from Flibble] +!62 = metadata !{i32 786689, null, metadata !"arg", null, i32 33554436, metadata !17, i32 0, null} ; [ DW_TAG_arg_variable ] [arg] [line 4] +!64 = metadata !{%struct.Flibble* undef} +!65 = metadata !{i32 786689, null, metadata !"this", null, i32 16777229, metadata !45, i32 1088, null} ; [ DW_TAG_arg_variable ] [this] [line 13]