[SimplifyCFG] Replace unreachable switch lookup table holes with poison #94990

DaMatrix · 2024-06-10T14:46:49Z

As discussed in #94468, this causes switch lookup table entries which are unreachable to be poison instead of filling them with a value from one of the reachable cases.

llvmbot · 2024-06-10T14:47:37Z

@llvm/pr-subscribers-llvm-transforms

Author: DaPorkchop_ (DaMatrix)

Changes

As discussed in #94468, this causes switch lookup table entries which are unreachable to be poison instead of filling them with a value from one of the reachable cases.

Full diff: https://github.com/llvm/llvm-project/pull/94990.diff

3 Files Affected:

(modified) llvm/lib/Transforms/Utils/SimplifyCFG.cpp (+24-8)
(modified) llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll (+131-3)
(modified) llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll (+3-3)

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 292739b6c5fda..50ef68ec02cc6 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6266,7 +6266,8 @@ SwitchLookupTable::SwitchLookupTable(
   assert(Values.size() && "Can't build lookup table without values!");
   assert(TableSize >= Values.size() && "Can't fit values in table!");
 
-  // If all values in the table are equal, this is that value.
+  // If all values in the table are equal, ignoring any values that are poison,
+  // this is that value.
   SingleValue = Values.begin()->second;
 
   Type *ValueType = Values.begin()->second->getType();
@@ -6281,8 +6282,15 @@ SwitchLookupTable::SwitchLookupTable(
     uint64_t Idx = (CaseVal->getValue() - Offset->getValue()).getLimitedValue();
     TableContents[Idx] = CaseRes;
 
-    if (CaseRes != SingleValue)
-      SingleValue = nullptr;
+    if (CaseRes != SingleValue) {
+      if (SingleValue && isa<PoisonValue>(SingleValue)) {
+        // All of the switch cases until now have returned poison; ignore them
+        // and use this value as the single constant value.
+        SingleValue = CaseRes;
+      } else if (!isa<PoisonValue>(CaseRes)) {
+        SingleValue = nullptr;
+      }
+    }
   }
 
   // Fill in any holes in the table with the default result.
@@ -6295,7 +6303,10 @@ SwitchLookupTable::SwitchLookupTable(
         TableContents[I] = DefaultValue;
     }
 
-    if (DefaultValue != SingleValue)
+    // If the default value is poison, all the holes are poison.
+    bool DefaultValueIsPoison = isa<PoisonValue>(DefaultValue);
+
+    if (DefaultValue != SingleValue && !DefaultValueIsPoison)
       SingleValue = nullptr;
   }
 
@@ -6322,6 +6333,9 @@ SwitchLookupTable::SwitchLookupTable(
       if (!ConstVal) {
         // This is an undef. We could deal with it, but undefs in lookup tables
         // are very seldom. It's probably not worth the additional complexity.
+        // TODO: In switches with holes and an unreachable default branch, this
+        //       will actually occur every time, as the holes will be filled
+        //       with poison.
         LinearMappingPossible = false;
         break;
       }
@@ -6752,8 +6766,8 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
 
   // If the table has holes but the default destination doesn't produce any
   // constant results, the lookup table entries corresponding to the holes will
-  // contain undefined values.
-  bool AllHolesAreUndefined = TableHasHoles && !HasDefaultResults;
+  // contain poison.
+  bool AllHolesArePoison = TableHasHoles && !HasDefaultResults;
 
   // If the default destination doesn't produce a constant result but is still
   // reachable, and the lookup table has holes, we need to use a mask to
@@ -6761,7 +6775,7 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
   // to the default case.
   // The mask is unnecessary if the table has holes but the default destination
   // is unreachable, as in that case the holes must also be unreachable.
-  bool NeedMask = AllHolesAreUndefined && DefaultIsReachable;
+  bool NeedMask = AllHolesArePoison && DefaultIsReachable;
   if (NeedMask) {
     // As an extra penalty for the validity test we require more cases.
     if (SI->getNumCases() < 4) // FIXME: Find best threshold value (benchmark).
@@ -6906,9 +6920,11 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
   for (PHINode *PHI : PHIs) {
     const ResultListTy &ResultList = ResultLists[PHI];
 
+    Type *ResultType = ResultList.begin()->second->getType();
+
     // Use any value to fill the lookup table holes.
     Constant *DV =
-        AllHolesAreUndefined ? ResultLists[PHI][0].second : DefaultResults[PHI];
+        AllHolesArePoison ? PoisonValue::get(ResultType) : DefaultResults[PHI];
     StringRef FuncName = Fn->getName();
     SwitchLookupTable Table(Mod, TableSize, TableIndexOffset, ResultList, DV,
                             DL, FuncName);
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
index 845c5008e3837..345476481f570 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -34,11 +34,12 @@ target triple = "x86_64-unknown-linux-gnu"
 ; CHECK: @switch.table.unreachable_case = private unnamed_addr constant [9 x i32] [i32 0, i32 0, i32 0, i32 2, i32 -1, i32 1, i32 1, i32 1, i32 1], align 4
 ; CHECK: @switch.table.unreachable_default = private unnamed_addr constant [4 x i32] [i32 42, i32 52, i32 1, i32 2], align 4
 ; CHECK: @switch.table.nodefaultnoholes = private unnamed_addr constant [4 x i32] [i32 55, i32 123, i32 0, i32 -1], align 4
-; CHECK: @switch.table.nodefaultwithholes = private unnamed_addr constant [6 x i32] [i32 55, i32 123, i32 0, i32 -1, i32 55, i32 -1], align 4
+; CHECK: @switch.table.nodefaultwithholes = private unnamed_addr constant [6 x i32] [i32 55, i32 123, i32 0, i32 -1, i32 poison, i32 -1], align 4
 ; CHECK: @switch.table.threecases = private unnamed_addr constant [3 x i32] [i32 10, i32 7, i32 5], align 4
-; CHECK: @switch.table.covered_switch_with_bit_tests = private unnamed_addr constant [8 x i32] [i32 2, i32 2, i32 2, i32 2, i32 2, i32 2, i32 1, i32 1], align 4
+; CHECK: @switch.table.covered_switch_with_bit_tests = private unnamed_addr constant [8 x i32] [i32 2, i32 2, i32 poison, i32 poison, i32 poison, i32 poison, i32 1, i32 1], align 4
 ; CHECK: @switch.table.signed_overflow1 = private unnamed_addr constant [4 x i32] [i32 3333, i32 4444, i32 1111, i32 2222], align 4
-; CHECK: @switch.table.signed_overflow2 = private unnamed_addr constant [4 x i32] [i32 3333, i32 4444, i32 2222, i32 2222], align 4
+; CHECK: @switch.table.signed_overflow2 = private unnamed_addr constant [4 x i32] [i32 3333, i32 4444, i32 poison, i32 2222], align 4
+; CHECK: @switch.table.linearmap_hole_unreachable_default = private unnamed_addr constant [5 x i32] [i32 1, i32 poison, i32 5, i32 7, i32 9], align 4
 ;.
 define i32 @f(i32 %c) {
 ; CHECK-LABEL: @f(
@@ -2151,3 +2152,130 @@ return:                                           ; preds = %sw.default, %entry,
   %retval.0 = phi { i8, i8 } [ undef, %entry ], [ undef, %entry ], [ undef, %entry ], [ %1, %sw.default ]
   ret { i8, i8 } %retval.0
 }
+
+; The switch has a hole which falls through to an unreachable default case, but it can still be optimized into a constant load because
+; the poison value used for the hole is ignored.
+define i32 @constant_hole_unreachable_default(i32 %x) {
+; CHECK-LABEL: @constant_hole_unreachable_default(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret i32 1
+;
+entry:
+  switch i32 %x, label %sw.default [
+  i32 0, label %bb0
+  i32 2, label %bb0
+  i32 3, label %bb0
+  i32 4, label %bb0
+  ]
+
+sw.default: unreachable
+bb0: br label %return
+
+return:
+  %res = phi i32 [ 1, %bb0 ]
+  ret i32 %res
+}
+
+; The switch has a hole which falls through to an unreachable default case and the first case explicitly returns poison, but it can still
+; be optimized into a constant load because the poison values are ignored.
+define i32 @constant_hole_unreachable_default_firstpoison(i32 %x) {
+; CHECK-LABEL: @constant_hole_unreachable_default_firstpoison(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret i32 1
+;
+entry:
+  switch i32 %x, label %sw.default [
+  i32 0, label %bb.poison
+  i32 2, label %bb0
+  i32 3, label %bb0
+  i32 4, label %bb0
+  ]
+
+sw.default: unreachable
+bb.poison: br label %return
+bb0: br label %return
+
+return:
+  %res = phi i32 [ poison, %bb.poison ], [ 1, %bb0 ]
+  ret i32 %res
+}
+
+; The switch has a hole which falls through to an unreachable default case and the first case explicitly returns poison, but it can still
+; be optimized into a constant load because the poison values are ignored.
+define i32 @constant_hole_unreachable_default_lastpoison(i32 %x) {
+; CHECK-LABEL: @constant_hole_unreachable_default_lastpoison(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret i32 1
+;
+entry:
+  switch i32 %x, label %sw.default [
+  i32 0, label %bb0
+  i32 2, label %bb0
+  i32 3, label %bb0
+  i32 4, label %bb.poison
+  ]
+
+sw.default: unreachable
+bb.poison: br label %return
+bb0: br label %return
+
+return:
+  %res = phi i32 [ poison, %bb.poison ], [ 1, %bb0 ]
+  ret i32 %res
+}
+
+; The switch has a hole which falls through to an unreachable default case, which prevents it from being optimized into a linear mapping 2*x+1.
+; TODO: We should add support for this, at least in certain cases.
+define i32 @linearmap_hole_unreachable_default(i32 %x) {
+; CHECK-LABEL: @linearmap_hole_unreachable_default(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [5 x i32], ptr @switch.table.linearmap_hole_unreachable_default, i32 0, i32 [[X:%.*]]
+; CHECK-NEXT:    [[SWITCH_LOAD:%.*]] = load i32, ptr [[SWITCH_GEP]], align 4
+; CHECK-NEXT:    ret i32 [[SWITCH_LOAD]]
+;
+entry:
+  switch i32 %x, label %sw.default [
+  i32 0, label %bb0
+  i32 2, label %bb2
+  i32 3, label %bb3
+  i32 4, label %bb4
+  ]
+
+sw.default: unreachable
+bb0: br label %return
+bb2: br label %return
+bb3: br label %return
+bb4: br label %return
+
+return:
+  %res = phi i32 [ 1, %bb0 ], [ 5, %bb2 ], [ 7, %bb3 ], [ 9, %bb4 ]
+  ret i32 %res
+}
+
+; The switch has a hole which falls through to an unreachable default case, but it can still be optimized into a bitmask extraction because
+; the poison value used for the hole is simply replaced with zero.
+define i1 @bitset_hole_unreachable_default(i32 %x) {
+; CHECK-LABEL: @bitset_hole_unreachable_default(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SWITCH_CAST:%.*]] = trunc i32 [[X:%.*]] to i5
+; CHECK-NEXT:    [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i5 [[SWITCH_CAST]], 1
+; CHECK-NEXT:    [[SWITCH_DOWNSHIFT:%.*]] = lshr i5 8, [[SWITCH_SHIFTAMT]]
+; CHECK-NEXT:    [[SWITCH_MASKED:%.*]] = trunc i5 [[SWITCH_DOWNSHIFT]] to i1
+; CHECK-NEXT:    ret i1 [[SWITCH_MASKED]]
+;
+entry:
+  switch i32 %x, label %sw.default [
+  i32 0, label %bb0
+  i32 2, label %bb0
+  i32 3, label %bb1
+  i32 4, label %bb0
+  ]
+
+sw.default: unreachable
+bb0: br label %return
+bb1: br label %return
+
+return:
+  %res = phi i1 [ 0, %bb0 ], [ 1, %bb1 ]
+  ret i1 %res
+}
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll
index 7988e3057a2c2..4ebf09ae3b127 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll
@@ -7,11 +7,11 @@ target triple = "i386-pc-linux-gnu"
 ;.
 ; CHECK: @switch.table.reachable_default_dense_0to31 = private unnamed_addr constant [32 x i32] [i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1], align 4
 ; CHECK: @switch.table.unreachable_default_dense_0to31 = private unnamed_addr constant [32 x i32] [i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1], align 4
-; CHECK: @switch.table.reachable_default_holes_0to31 = private unnamed_addr constant [32 x i32] [i32 0, i32 7, i32 6, i32 0, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 0, i32 2, i32 1, i32 0, i32 7, i32 0, i32 5, i32 4, i32 3, i32 2, i32 0, i32 0, i32 7, i32 6, i32 5, i32 0, i32 3, i32 2, i32 1], align 4
-; CHECK: @switch.table.unreachable_default_holes_0to31 = private unnamed_addr constant [32 x i32] [i32 0, i32 7, i32 6, i32 0, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 0, i32 2, i32 1, i32 0, i32 7, i32 0, i32 5, i32 4, i32 3, i32 2, i32 0, i32 0, i32 7, i32 6, i32 5, i32 0, i32 3, i32 2, i32 1], align 4
+; CHECK: @switch.table.reachable_default_holes_0to31 = private unnamed_addr constant [32 x i32] [i32 0, i32 7, i32 6, i32 poison, i32 4, i32 3, i32 2, i32 1, i32 poison, i32 7, i32 6, i32 5, i32 4, i32 poison, i32 2, i32 1, i32 0, i32 7, i32 poison, i32 5, i32 4, i32 3, i32 2, i32 poison, i32 0, i32 7, i32 6, i32 5, i32 poison, i32 3, i32 2, i32 1], align 4
+; CHECK: @switch.table.unreachable_default_holes_0to31 = private unnamed_addr constant [32 x i32] [i32 0, i32 7, i32 6, i32 poison, i32 4, i32 3, i32 2, i32 1, i32 poison, i32 7, i32 6, i32 5, i32 4, i32 poison, i32 2, i32 1, i32 0, i32 7, i32 poison, i32 5, i32 4, i32 3, i32 2, i32 poison, i32 0, i32 7, i32 6, i32 5, i32 poison, i32 3, i32 2, i32 1], align 4
 ; CHECK: @switch.table.reachable_default_dense_0to32 = private unnamed_addr constant [33 x i32] [i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0], align 4
 ; CHECK: @switch.table.unreachable_default_dense_0to32 = private unnamed_addr constant [33 x i32] [i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0], align 4
-; CHECK: @switch.table.unreachable_default_holes_0to32 = private unnamed_addr constant [33 x i32] [i32 0, i32 7, i32 6, i32 0, i32 4, i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 0, i32 2, i32 1, i32 0, i32 7, i32 0, i32 5, i32 4, i32 3, i32 2, i32 0, i32 0, i32 7, i32 6, i32 5, i32 0, i32 3, i32 2, i32 1, i32 0], align 4
+; CHECK: @switch.table.unreachable_default_holes_0to32 = private unnamed_addr constant [33 x i32] [i32 0, i32 7, i32 6, i32 poison, i32 4, i32 3, i32 2, i32 1, i32 poison, i32 7, i32 6, i32 5, i32 4, i32 poison, i32 2, i32 1, i32 0, i32 7, i32 poison, i32 5, i32 4, i32 3, i32 2, i32 poison, i32 0, i32 7, i32 6, i32 5, i32 poison, i32 3, i32 2, i32 1, i32 0], align 4
 ;.
 define i32 @reachable_default_dense_0to31(i32 %x, i32 %y) {
 ; CHECK-LABEL: @reachable_default_dense_0to31(

dianqk

I'll review this PR again over the weekend.

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

dianqk · 2024-06-12T23:59:24Z

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -6322,6 +6333,9 @@ SwitchLookupTable::SwitchLookupTable(
      if (!ConstVal) {
        // This is an undef. We could deal with it, but undefs in lookup tables
        // are very seldom. It's probably not worth the additional complexity.
+        // TODO: In switches with holes and an unreachable default branch, this


Do you want to finish this TODO in this PR? If not, could you change the poison values back to the first value? I'm concerned this might cause some regressions.

I wasn't planning on fixing it in this PR, since it seemed like too big of a change. I've got another PR lined up which fixes this TODO, which I was planning to open as soon as this gets merged. Would you prefer I made that part of this PR?

It's fine with me, but I hope you can restore the unhandled cases to their previous values in this PR.

I've changed this as well. Is the new version what you had in mind?

I think you can set it to the first value here:

llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp

Line 6268 in d75f9dd

TableContents[Idx] = CaseRes;

. Your test cases reminded me that we can directly provide undef/poison, so this might not cause significant regressions. Others might have different opinions on this, so I'll request comments from them after you address the poison and undef mixing issue.

llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll

DaMatrix · 2024-12-19T13:18:32Z

Rebasing to a much more recent commit to hopefully prevent GitHub Actions from timing out.

github-actions · 2024-12-19T13:21:52Z

⚠️ undef deprecator found issues in your code. ⚠️

You can test this locally with the following command:

git diff -U0 --pickaxe-regex -S '([^a-zA-Z0-9#_-]undef[^a-zA-Z0-9_-]|UndefValue::get)' f8d270474c14c6705c77971494505dbe4b6d55ae 659c67692818151c2f7796ce52325aef7fd6cdef llvm/lib/Transforms/Utils/SimplifyCFG.cpp llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll

The following files introduce new uses of undef:

llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll

Undef is now deprecated and should only be used in the rare cases where no replacement is possible. For example, a load of uninitialized memory yields undef. You should use poison values for placeholders instead.

In tests, avoid using undef and having tests that trigger undefined behavior. If you need an operand with some unimportant value, you can add a new argument to the function and use that instead.

For example, this is considered a bad practice:

define void @fn() {
  ...
  br i1 undef, ...
}

Please use the following instead:

define void @fn(i1 %cond) {
  ...
  br i1 %cond, ...
}

Please refer to the Undefined Behavior Manual for more information.

DaMatrix · 2024-12-19T13:27:07Z

Oh... that's annoying, how am I supposed to differentiate poison from undef if I'm no longer allowed to add new usages of undef?

dianqk · 2024-12-19T13:43:24Z

Oh... that's annoying, how am I supposed to differentiate poison from undef if I'm no longer allowed to add new usages of undef?

I think you can only check if it is a poison. Please keep these test cases to prevent mis-compile.

DaMatrix · 2024-12-19T14:26:03Z

Okay, so I should remove all the logic for handling combinations of undef and poison, and instead assume that the lookup table values will always be either a ConstantInt or a poison?

DaMatrix · 2024-12-19T15:04:53Z

Okay, this new commit will still fail that check as there are (necessarily) new occurrences of undef in the tests, but the actual code no longer contains any new references to undef.

dianqk

LGTM. If no one else comments, I'll merge it next Tuesday.

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

dianqk · 2024-12-20T11:07:58Z

llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll

-; CHECK: @switch.table.signed_overflow2 = private unnamed_addr constant [4 x i32] [i32 3333, i32 4444, i32 2222, i32 2222], align 4
+; CHECK: @switch.table.signed_overflow2 = private unnamed_addr constant [4 x i32] [i32 3333, i32 4444, i32 poison, i32 2222], align 4
+; CHECK: @switch.table.constant_hole_unreachable_default_firstundef = private unnamed_addr constant [5 x i32] [i32 undef, i32 poison, i32 1, i32 1, i32 1], align 4
+; CHECK: @switch.table.constant_hole_unreachable_default_lastundef = private unnamed_addr constant [5 x i32] [i32 1, i32 poison, i32 1, i32 1, i32 undef], align 4


@dtcxzyw I don't know what impact this has on real-world code. Do you think it's worth running llvm-opt-benchmark?

github-actions · 2024-12-22T11:24:28Z

✅ With the latest revision this PR passed the C/C++ code formatter.

Co-authored-by: DianQK <[email protected]>

llvm-ci · 2024-12-26T00:01:49Z

LLVM Buildbot has detected a new failure on builder clang-aarch64-sve-vla running on linaro-g3-03 while building llvm at step 1 "Checkout lnt".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/17/builds/4896

Here is the relevant piece of the build log for the reference

Step 1 (Checkout lnt) failure: update (failure)
git version 2.34.1
From https://github.com/llvm/llvm-lnt
 * branch            HEAD       -> FETCH_HEAD
fatal: Unable to create '/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/test/lnt/.git/index.lock': File exists.

Another git process seems to be running in this repository, e.g.
an editor opened by 'git commit'. Please make sure all processes
are terminated then try again. If it still fails, a git process
may have crashed in this repository earlier:
remove the file manually to continue.
From https://github.com/llvm/llvm-lnt
 * branch            HEAD       -> FETCH_HEAD
fatal: Unable to create '/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/test/lnt/.git/index.lock': File exists.

Another git process seems to be running in this repository, e.g.
an editor opened by 'git commit'. Please make sure all processes
are terminated then try again. If it still fails, a git process
may have crashed in this repository earlier:
remove the file manually to continue.

dianqk · 2024-12-26T05:14:24Z

@nikic @dtcxzyw @RalfJung
Per https://discourse.llvm.org/t/rfc-add-nopoison-attribute-metadata/79833, how should we think about this PR?

Local branch amd-gfx 0756140 Merged main:5712e293fb31 into amd-gfx:5f712560902a Remote branch main cea738b [SimplifyCFG] Replace unreachable switch lookup table holes with poison (llvm#94990) Change-Id: If1d143783b7f74b6d146934b0cf9fc3fe20ac6b4

llvmbot added the llvm:transforms label Jun 10, 2024

dtcxzyw requested review from nikic and dianqk June 10, 2024 15:02

dianqk reviewed Jun 13, 2024

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DaMatrix force-pushed the switch-lookup-tables-poison-holes branch 3 times, most recently from 95f0f20 to e30a331 Compare June 23, 2024 16:28

dianqk reviewed Jun 26, 2024

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llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll Outdated Show resolved Hide resolved

DaMatrix force-pushed the switch-lookup-tables-poison-holes branch from e30a331 to d6098d6 Compare December 18, 2024 12:25

DaMatrix force-pushed the switch-lookup-tables-poison-holes branch from d6098d6 to 4858b9c Compare December 19, 2024 13:18

DaMatrix added 2 commits December 19, 2024 15:40

[SimplifyCFG] Lookup table test cases

ac23a90

[SimplifyCFG] Replace unreachable switch lookup table holes with poison

f9d54a5

DaMatrix force-pushed the switch-lookup-tables-poison-holes branch from 4858b9c to f9d54a5 Compare December 19, 2024 15:02

dianqk approved these changes Dec 20, 2024

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Update llvm/lib/Transforms/Utils/SimplifyCFG.cpp

659c676

Co-authored-by: DianQK <[email protected]>

DaMatrix force-pushed the switch-lookup-tables-poison-holes branch from 65dd653 to 659c676 Compare December 22, 2024 11:29

dianqk merged commit cea738b into llvm:main Dec 25, 2024
7 of 8 checks passed

dianqk requested a review from dtcxzyw December 26, 2024 05:11

DaMatrix deleted the switch-lookup-tables-poison-holes branch December 27, 2024 10:06

[SimplifyCFG] Replace unreachable switch lookup table holes with poison #94990

[SimplifyCFG] Replace unreachable switch lookup table holes with poison #94990

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