GlobalISel: put debug info for static allocas in the MachineFunction.

The good reason to do this is that static allocas are pretty simple to handle
(especially at -O0) and avoiding tracking DBG_VALUEs throughout the pipeline
should give some kind of performance benefit.

The bad reason is that the debug pipeline is an unholy mess of implicit
contracts, where determining whether "DBG_VALUE %reg, imm" actually implies a
load or not involves the services of at least 3 soothsayers and the sacrifice
of at least one chicken.  And it still gets it wrong if the variable is at SP
directly.

llvm-svn: 297410

Author: TNorthover

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

@@ -598,18 +598,18 @@ bool IRTranslator::translateKnownIntrinsic(const CallInst &CI, Intrinsic::ID ID,
       return true;
     }
 
-    unsigned Reg = getOrCreateVReg(*Address);
-    auto RegDef = MRI->def_instr_begin(Reg);
     assert(DI.getVariable()->isValidLocationForIntrinsic(
                MIRBuilder.getDebugLoc()) &&
            "Expected inlined-at fields to agree");
-
-    if (RegDef != MRI->def_instr_end() &&
-        RegDef->getOpcode() == TargetOpcode::G_FRAME_INDEX) {
-      MIRBuilder.buildFIDbgValue(RegDef->getOperand(1).getIndex(),
-                                 DI.getVariable(), DI.getExpression());
+    auto AI = dyn_cast<AllocaInst>(Address);
+    if (AI && AI->isStaticAlloca()) {
+      // Static allocas are tracked at the MF level, no need for DBG_VALUE
+      // instructions (in fact, they get ignored if they *do* exist).
+      MF->setVariableDbgInfo(DI.getVariable(), DI.getExpression(),
+                             getOrCreateFrameIndex(*AI), DI.getDebugLoc());
     } else
-      MIRBuilder.buildDirectDbgValue(Reg, DI.getVariable(), DI.getExpression());
+      MIRBuilder.buildDirectDbgValue(getOrCreateVReg(*Address),
+                                     DI.getVariable(), DI.getExpression());
     return true;
   }
   case Intrinsic::vaend:

llvm/lib/CodeGen/MachineFunction.cpp

@@ -169,6 +169,7 @@ void MachineFunction::clear() {
   InstructionRecycler.clear(Allocator);
   OperandRecycler.clear(Allocator);
   BasicBlockRecycler.clear(Allocator);
+  VariableDbgInfos.clear();
   if (RegInfo) {
     RegInfo->~MachineRegisterInfo();
     Allocator.Deallocate(RegInfo);

llvm/test/CodeGen/AArch64/GlobalISel/debug-insts.ll

@@ -1,8 +1,10 @@
 ; RUN: llc -global-isel -mtriple=aarch64 %s -stop-after=irtranslator -o - | FileCheck %s
-
+; RUN: llc -mtriple=aarch64 -global-isel --global-isel-abort=0 -o /dev/null
 
 ; CHECK-LABEL: name: debug_declare
-; CHECK: DBG_VALUE %stack.0.in.addr, 0, !11, !12, debug-location !13
+; CHECK: stack:
+; CHECK:    - { id: {{.*}}, name: in.addr, offset: {{.*}}, size: {{.*}}, alignment: {{.*}}, di-variable: '!11',
+; CHECK-NEXT:   di-expression: '!12', di-location: '!13' }
 ; CHECK: DBG_VALUE debug-use %0(s32), debug-use _, !11, !12, debug-location !13
 define void @debug_declare(i32 %in) #0 !dbg !7 {
 entry:
@@ -13,6 +15,15 @@ entry:
   ret void, !dbg !14
 }
 
+; CHECK-LABEL: name: debug_declare_vla
+; CHECK: DBG_VALUE debug-use %{{[0-9]+}}(p0), debug-use _, !11, !12, debug-location !13
+define void @debug_declare_vla(i32 %in) #0 !dbg !7 {
+entry:
+  %vla.addr = alloca i32, i32 %in
+  call void @llvm.dbg.declare(metadata i32* %vla.addr, metadata !11, metadata !12), !dbg !13
+  ret void, !dbg !14
+}
+
 ; CHECK-LABEL: name: debug_value
 ; CHECK: [[IN:%[0-9]+]](s32) = COPY %w0
 define void @debug_value(i32 %in) #0 !dbg !7 {