[Mlir-commits] [mlir] 9dd0eb9 - [mlir][llvm] Drop unreachable basic block during import (#78467)
llvmlistbot at llvm.org
llvmlistbot at llvm.org
Fri Jan 19 02:11:01 PST 2024
Author: Tobias Gysi
Date: 2024-01-19T11:10:57+01:00
New Revision: 9dd0eb9c9c207e7ea17912616c5cea58aa5c514d
URL: https://github.com/llvm/llvm-project/commit/9dd0eb9c9c207e7ea17912616c5cea58aa5c514d
DIFF: https://github.com/llvm/llvm-project/commit/9dd0eb9c9c207e7ea17912616c5cea58aa5c514d.diff
LOG: [mlir][llvm] Drop unreachable basic block during import (#78467)
This revision updates the LLVM IR import to support unreachable basic
blocks. An unreachable block may dominate itself and a value defined
inside the block may thus be used before its definition. The import does
not support such dependencies. We thus delete the unreachable basic
blocks before the import. This is possible since MLIR does not have
basic block labels that can be reached using an indirect call and
unreachable blocks can indeed be deleted safely.
Additionally, add a small poison constant import test.
Added:
mlir/test/Target/LLVMIR/Import/unreachable-blocks.ll
Modified:
mlir/lib/Target/LLVMIR/ModuleImport.cpp
mlir/test/Target/LLVMIR/Import/constant.ll
mlir/test/Target/LLVMIR/Import/exception.ll
Removed:
################################################################################
diff --git a/mlir/lib/Target/LLVMIR/ModuleImport.cpp b/mlir/lib/Target/LLVMIR/ModuleImport.cpp
index e905408a1e0897..928d8077175ccf 100644
--- a/mlir/lib/Target/LLVMIR/ModuleImport.cpp
+++ b/mlir/lib/Target/LLVMIR/ModuleImport.cpp
@@ -26,6 +26,7 @@
#include "mlir/Interfaces/DataLayoutInterfaces.h"
#include "mlir/Tools/mlir-translate/Translation.h"
+#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/StringSet.h"
@@ -132,18 +133,17 @@ static LogicalResult convertInstructionImpl(OpBuilder &odsBuilder,
return failure();
}
-/// Get a topologically sorted list of blocks for the given function.
+/// Get a topologically sorted list of blocks for the given basic blocks.
static SetVector<llvm::BasicBlock *>
-getTopologicallySortedBlocks(llvm::Function *func) {
+getTopologicallySortedBlocks(ArrayRef<llvm::BasicBlock *> basicBlocks) {
SetVector<llvm::BasicBlock *> blocks;
- for (llvm::BasicBlock &bb : *func) {
- if (!blocks.contains(&bb)) {
- llvm::ReversePostOrderTraversal<llvm::BasicBlock *> traversal(&bb);
+ for (llvm::BasicBlock *basicBlock : basicBlocks) {
+ if (!blocks.contains(basicBlock)) {
+ llvm::ReversePostOrderTraversal<llvm::BasicBlock *> traversal(basicBlock);
blocks.insert(traversal.begin(), traversal.end());
}
}
- assert(blocks.size() == func->size() && "some blocks are not sorted");
-
+ assert(blocks.size() == basicBlocks.size() && "some blocks are not sorted");
return blocks;
}
@@ -1859,11 +1859,26 @@ LogicalResult ModuleImport::processFunction(llvm::Function *func) {
if (func->isDeclaration())
return success();
- // Eagerly create all blocks.
- for (llvm::BasicBlock &bb : *func) {
- Block *block =
- builder.createBlock(&funcOp.getBody(), funcOp.getBody().end());
- mapBlock(&bb, block);
+ // Collect the set of basic blocks reachable from the function's entry block.
+ // This step is crucial as LLVM IR can contain unreachable blocks that
+ // self-dominate. As a result, an operation might utilize a variable it
+ // defines, which the import does not support. Given that MLIR lacks block
+ // label support, we can safely remove unreachable blocks, as there are no
+ // indirect branch instructions that could potentially target these blocks.
+ llvm::df_iterator_default_set<llvm::BasicBlock *> reachable;
+ for (llvm::BasicBlock *basicBlock : llvm::depth_first_ext(func, reachable))
+ (void)basicBlock;
+
+ // Eagerly create all reachable blocks.
+ SmallVector<llvm::BasicBlock *> reachableBasicBlocks;
+ for (llvm::BasicBlock &basicBlock : *func) {
+ // Skip unreachable blocks.
+ if (!reachable.contains(&basicBlock))
+ continue;
+ Region &body = funcOp.getBody();
+ Block *block = builder.createBlock(&body, body.end());
+ mapBlock(&basicBlock, block);
+ reachableBasicBlocks.push_back(&basicBlock);
}
// Add function arguments to the entry block.
@@ -1876,10 +1891,11 @@ LogicalResult ModuleImport::processFunction(llvm::Function *func) {
// Process the blocks in topological order. The ordered traversal ensures
// operands defined in a dominating block have a valid mapping to an MLIR
// value once a block is translated.
- SetVector<llvm::BasicBlock *> blocks = getTopologicallySortedBlocks(func);
+ SetVector<llvm::BasicBlock *> blocks =
+ getTopologicallySortedBlocks(reachableBasicBlocks);
setConstantInsertionPointToStart(lookupBlock(blocks.front()));
- for (llvm::BasicBlock *bb : blocks)
- if (failed(processBasicBlock(bb, lookupBlock(bb))))
+ for (llvm::BasicBlock *basicBlock : blocks)
+ if (failed(processBasicBlock(basicBlock, lookupBlock(basicBlock))))
return failure();
// Process the debug intrinsics that require a delayed conversion after
diff --git a/mlir/test/Target/LLVMIR/Import/constant.ll b/mlir/test/Target/LLVMIR/Import/constant.ll
index cd2d00ec0aa783..3c46f5b20c31ca 100644
--- a/mlir/test/Target/LLVMIR/Import/constant.ll
+++ b/mlir/test/Target/LLVMIR/Import/constant.ll
@@ -47,6 +47,16 @@ define void @undef_constant(i32 %arg0) {
; // -----
+; CHECK-LABEL: @poison_constant
+define void @poison_constant(double %arg0) {
+ ; CHECK: %[[POISON:.+]] = llvm.mlir.poison : f64
+ ; CHECK: llvm.fadd %[[POISON]], %{{.*}} : f64
+ %1 = fadd double poison, %arg0
+ ret void
+}
+
+; // -----
+
; CHECK-LABEL: @null_constant
define ptr @null_constant() {
; CHECK: %[[NULL:[0-9]+]] = llvm.mlir.zero : !llvm.ptr
diff --git a/mlir/test/Target/LLVMIR/Import/exception.ll b/mlir/test/Target/LLVMIR/Import/exception.ll
index de227645cc15bb..440d89ec147f76 100644
--- a/mlir/test/Target/LLVMIR/Import/exception.ll
+++ b/mlir/test/Target/LLVMIR/Import/exception.ll
@@ -12,34 +12,35 @@ define i32 @invokeLandingpad() personality ptr @__gxx_personality_v0 {
; CHECK: %[[a1:[0-9]+]] = llvm.mlir.addressof @_ZTIii : !llvm.ptr
; CHECK: %[[a3:[0-9]+]] = llvm.alloca %{{[0-9]+}} x i8 {alignment = 1 : i64} : (i32) -> !llvm.ptr
%1 = alloca i8
- ; CHECK: llvm.invoke @foo(%[[a3]]) to ^bb2 unwind ^bb1 : (!llvm.ptr) -> ()
- invoke void @foo(ptr %1) to label %4 unwind label %2
+ ; CHECK: llvm.invoke @foo(%[[a3]]) to ^[[bb1:.*]] unwind ^[[bb4:.*]] : (!llvm.ptr) -> ()
+ invoke void @foo(ptr %1) to label %bb1 unwind label %bb4
-; CHECK: ^bb1:
+; CHECK: ^[[bb1]]:
+bb1:
+ ; CHECK: %{{[0-9]+}} = llvm.invoke @bar(%[[a3]]) to ^[[bb2:.*]] unwind ^[[bb4]] : (!llvm.ptr) -> !llvm.ptr
+ %2 = invoke ptr @bar(ptr %1) to label %bb2 unwind label %bb4
+
+; CHECK: ^[[bb2]]:
+bb2:
+ ; CHECK: llvm.invoke @vararg_foo(%[[a3]], %{{.*}}) to ^[[bb3:.*]] unwind ^[[bb4]] vararg(!llvm.func<void (ptr, ...)>) : (!llvm.ptr, i32) -> ()
+ invoke void (ptr, ...) @vararg_foo(ptr %1, i32 0) to label %bb3 unwind label %bb4
+
+; CHECK: ^[[bb3]]:
+bb3:
+ ; CHECK: llvm.invoke %{{.*}}(%[[a3]], %{{.*}}) to ^[[bb5:.*]] unwind ^[[bb4]] vararg(!llvm.func<void (ptr, ...)>) : !llvm.ptr, (!llvm.ptr, i32) -> ()
+ invoke void (ptr, ...) undef(ptr %1, i32 0) to label %bb5 unwind label %bb4
+
+; CHECK: ^[[bb4]]:
+bb4:
; CHECK: %{{[0-9]+}} = llvm.landingpad (catch %{{[0-9]+}} : !llvm.ptr) (catch %[[a1]] : !llvm.ptr) (filter %{{[0-9]+}} : !llvm.array<1 x i1>) : !llvm.struct<(ptr, i32)>
%3 = landingpad { ptr, i32 } catch ptr @_ZTIi catch ptr @_ZTIii
filter [1 x i1] [i1 1]
resume { ptr, i32 } %3
-; CHECK: ^bb2:
+; CHECK: ^[[bb5]]:
+bb5:
; CHECK: llvm.return %{{[0-9]+}} : i32
ret i32 1
-
-; CHECK: ^bb3:
- ; CHECK: %{{[0-9]+}} = llvm.invoke @bar(%[[a3]]) to ^bb2 unwind ^bb1 : (!llvm.ptr) -> !llvm.ptr
- %6 = invoke ptr @bar(ptr %1) to label %4 unwind label %2
-
-; CHECK: ^bb4:
- ; CHECK: llvm.invoke @vararg_foo(%[[a3]], %{{.*}}) to ^bb2 unwind ^bb1 vararg(!llvm.func<void (ptr, ...)>) : (!llvm.ptr, i32) -> ()
- invoke void (ptr, ...) @vararg_foo(ptr %1, i32 0) to label %4 unwind label %2
-
-; CHECK: ^bb5:
- ; CHECK: llvm.invoke %{{.*}}(%[[a3]], %{{.*}}) to ^bb2 unwind ^bb1 vararg(!llvm.func<void (ptr, ...)>) : !llvm.ptr, (!llvm.ptr, i32) -> ()
- invoke void (ptr, ...) undef(ptr %1, i32 0) to label %4 unwind label %2
-
-; CHECK: ^bb6:
- ; CHECK: llvm.return %{{[0-9]+}} : i32
- ret i32 0
}
declare i32 @foo2()
diff --git a/mlir/test/Target/LLVMIR/Import/unreachable-blocks.ll b/mlir/test/Target/LLVMIR/Import/unreachable-blocks.ll
new file mode 100644
index 00000000000000..8a84f4b5c19b8d
--- /dev/null
+++ b/mlir/test/Target/LLVMIR/Import/unreachable-blocks.ll
@@ -0,0 +1,35 @@
+; RUN: mlir-translate -import-llvm %s | FileCheck %s
+
+; Test unreachable blocks are dropped.
+
+; CHECK-LABEL: llvm.func @unreachable_block
+define void @unreachable_block(float %0) {
+.entry:
+ ; CHECK: llvm.return
+ ret void
+
+unreachable:
+ ; CHECK-NOT: llvm.fadd
+ %1 = fadd float %0, %1
+ br label %unreachable
+}
+
+; Test unreachable blocks with back edges are supported.
+
+; CHECK-LABEL: llvm.func @back_edge
+define i32 @back_edge(i32 %0) {
+.entry:
+ ; CHECK: llvm.br ^[[RET:.*]](%{{.*}})
+ br label %ret
+ret:
+ ; CHECK: ^[[RET]](%{{.*}}: i32)
+ %1 = phi i32 [ %0, %.entry ], [ %2, %unreachable ]
+ ; CHECK: llvm.return %{{.*}} : i32
+ ret i32 %1
+
+unreachable:
+ ; CHECK-NOT: add
+ %2 = add i32 %0, %2
+ %3 = icmp eq i32 %2, 42
+ br i1 %3, label %ret, label %unreachable
+}
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