[StackColoring] Delete dead stack slots (#75351)

deletes slots that have lifetime markers and the lifetime ranges are empty.

Author: mohammed-nurulhoque

llvm/lib/CodeGen/StackColoring.cpp

@@ -900,6 +900,15 @@ void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
   unsigned FixedMemOp = 0;
   unsigned FixedDbg = 0;
 
+  // Remove debug information for deleted slots.
+  erase_if(MF->getVariableDbgInfo(), [&](auto &VI) {
+    if (!VI.inStackSlot())
+      return false;
+    int Slot = VI.getStackSlot();
+    return Slot >= 0 && Intervals[Slot]->empty() &&
+           InterestingSlots.test(Slot) && !ConservativeSlots.test(Slot);
+  });
+
   // Remap debug information that refers to stack slots.
   for (auto &VI : MF->getVariableDbgInfo()) {
     if (!VI.Var || !VI.inStackSlot())
@@ -1250,8 +1259,15 @@ bool StackColoring::runOnMachineFunction(MachineFunction &Func) {
 
   // Do not bother looking at empty intervals.
   for (unsigned I = 0; I < NumSlots; ++I) {
-    if (Intervals[SortedSlots[I]]->empty())
+    int Slot = SortedSlots[I];
+    if (Intervals[Slot]->empty()) {
+      if (InterestingSlots.test(Slot) && !ConservativeSlots.test(Slot)) {
+        RemovedSlots += 1;
+        ReducedSize += MFI->getObjectSize(Slot);
+        MFI->RemoveStackObject(Slot);
+      }
       SortedSlots[I] = -1;
+    }
   }
 
   // This is a simple greedy algorithm for merging allocas. First, sort the
@@ -1339,7 +1355,7 @@ bool StackColoring::runOnMachineFunction(MachineFunction &Func) {
 
   // Scan the entire function and update all machine operands that use frame
   // indices to use the remapped frame index.
-  if (!SlotRemap.empty()) {
+  if (RemovedSlots > 0) {
     expungeSlotMap(SlotRemap, NumSlots);
     remapInstructions(SlotRemap);
   }

llvm/test/CodeGen/PowerPC/aix32-cc-abi-vaarg.ll

@@ -347,7 +347,6 @@ entry:
 
 ; 32BIT-LABEL:   stack:
 ; 32BIT-DAG:     - { id: 0, name: arg1, type: default, offset: 0, size: 4, alignment: 4,
-; 32BIT-DAG:     - { id: 1, name: arg2, type: default, offset: 0, size: 4, alignment: 4,
 ; 32BIT-DAG:     - { id: 2, name: '', type: default, offset: 0, size: 8, alignment: 8,
 ; 32BIT-DAG:     - { id: 3, name: '', type: default, offset: 0, size: 8, alignment: 8,
 

llvm/test/CodeGen/PowerPC/aix64-cc-abi-vaarg.ll

@@ -138,9 +138,7 @@
 ; 64BIT-LABEL:   fixedStack:
 ; 64BIT-DAG:     - { id: 0, type: default, offset: 112, size: 8, alignment: 16, stack-id: default,
 
-; 64BIT-LABEL:   stack:
-; 64BIT-DAG:     - { id: 0, name: arg1, type: default, offset: 0, size: 8, alignment: 8,
-; 64BIT-DAG:     - { id: 1, name: arg2, type: default, offset: 0, size: 8, alignment: 8,
+; 64BIT-LABEL:   stack: []
 
 ; 64BIT-LABEL:   body:             |
 ; 64BIT-DAG:     liveins: $x3, $x4, $x5, $x6, $x7, $x8, $x9, $x10
@@ -305,9 +303,7 @@
 ; 64BIT-LABEL:   fixedStack:
 ; 64BIT-DAG:       - { id: 0, type: default, offset: 152, size: 8
 
-; 64BIT-LABEL:   stack:
-; 64BIT-DAG:       - { id: 0, name: arg1, type: default, offset: 0, size: 8
-; 64BIT-DAG:       - { id: 1, name: arg2, type: default, offset: 0, size: 8
+; 64BIT-LABEL:   stack:           []
 
 ; 64BIT-LABEL:     body:             |
 ; 64BIT-DAG:       liveins: $f1, $f2, $f3, $f4, $f5, $f6, $f7, $f8, $f9, $f10, $f11, $f12, $f13

llvm/test/CodeGen/RISCV/dead-stack-slot.ll

@@ -0,0 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s
+; RUN: llc -mtriple=riscv64 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s
+
+; Remove the lifetime-marked alloca, but not the unmarked one.
+define signext i32 @f1() nounwind {
+; CHECK-LABEL: f1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addi sp, sp, -32
+; CHECK-NEXT:    li a0, 0
+; CHECK-NEXT:    addi sp, sp, 32
+; CHECK-NEXT:    ret
+  %1 = alloca [32 x i8], align 4
+  %2 = alloca [32 x i8], align 4
+  %3 = getelementptr inbounds [32 x i8], ptr %1, i64 0, i64 0
+  call void @llvm.lifetime.start.p0(i64 32, ptr nonnull %3)
+  call void @llvm.lifetime.end.p0(i64 32, ptr nonnull %3)
+  ret i32 0
+}
+
+declare void @llvm.lifetime.start.p0(i64 immarg, ptr nocapture)
+declare void @llvm.lifetime.end.p0(i64 immarg, ptr nocapture)
+

llvm/test/CodeGen/X86/StackColoring-tbaa.mir

@@ -53,7 +53,7 @@ body:             |
     ; CHECK: [[LEA64r:%[0-9]+]]:gr64 = nuw LEA64r %stack.1.agg, 1, $noreg, 24, $noreg
     ; CHECK-NEXT: CMP8mi %stack.1.agg, 1, $noreg, 47, $noreg, 0, implicit-def $eflags :: (dereferenceable load (s8) from %ir.a22, !tbaa !2)
     ; CHECK-NEXT: [[CMOV64rm:%[0-9]+]]:gr64 = CMOV64rm [[LEA64r]], %stack.1.agg, 1, $noreg, 24, $noreg, 8, implicit $eflags :: (dereferenceable load (s64) from %ir.a2)
-    ; CHECK-NEXT: [[MOV8rm:%[0-9]+]]:gr8 = MOV8rm killed [[CMOV64rm]], 1, $noreg, 16, $noreg :: (load (s8) from %ir.add.ptr.i, !tbaa !2)
+    ; CHECK-NEXT: [[MOV8rm:%[0-9]+]]:gr8 = MOV8rm killed [[CMOV64rm]], 1, $noreg, 16, $noreg :: (load (s8) from %ir.add.ptr.i)
     ; CHECK-NEXT: $al = COPY [[MOV8rm]]
     ; CHECK-NEXT: RET 0, $al
     LIFETIME_START %stack.0.padding

llvm/test/DebugInfo/COFF/lexicalblock.ll

@@ -63,32 +63,12 @@
 ; CHECK: LocalSym {
 ; CHECK:   VarName: localA
 ; CHECK: }
-; CHECK: LocalSym {
-; CHECK:   VarName: localB
-; CHECK: }
-; CHECK: BlockSym {
-; CHECK:   Kind: S_BLOCK32 {{.*}}
-; CHECK:   BlockName: 
-; CHECK: }
-; CHECK: ScopeEndSym {
-; CHECK:   Kind: S_END {{.*}}
-; CHECK: }
-; CHECK: BlockSym {
-; CHECK:   Kind: S_BLOCK32 {{.*}}
-; CHECK:   BlockName: 
-; CHECK: }
-; CHECK: ScopeEndSym {
-; CHECK:   Kind: S_END {{.*}}
-; CHECK: }
 ; CHECK: BlockSym {
 ; CHECK:   Kind: S_BLOCK32 {{.*}}
 ; CHECK:   BlockName: 
 ; CHECK: }
-; CHECK: ScopeEndSym {
-; CHECK: }
-; CHECK: BlockSym {
-; CHECK:   Kind: S_BLOCK32 {{.*}}
-; CHECK:   BlockName: 
+; CHECK: LocalSym {
+; CHECK:   VarName: localB
 ; CHECK: }
 ; CHECK: ScopeEndSym {
 ; CHECK:   Kind: S_END {{.*}}