[PATCH] D83584: [AMDGPU] Move LowerSwitch pass to CodeGenPrepare.

[Christudasan Devadasan via Phabricator via llvm-commits]

cdevadas updated this revision to Diff 277193.
cdevadas added a comment.

Incorporated the suggestions.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D83584/new/

https://reviews.llvm.org/D83584

Files:
  llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
  llvm/test/CodeGen/AMDGPU/switch-default-block-unreachable.ll


Index: llvm/test/CodeGen/AMDGPU/switch-default-block-unreachable.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AMDGPU/switch-default-block-unreachable.ll
@@ -0,0 +1,60 @@
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx908 -verify-machineinstrs -stop-after=amdgpu-isel -o - %s | FileCheck -check-prefix=GCN %s
+define void @test() #1 {
+  ; Clean up the unreachable blocks introduced with LowerSwitch pass.
+  ; This test ensures that, in the pass flow, UnreachableBlockElim pass
+  ; follows the LowerSwitch. Otherwise, this testcase will crash
+  ; immediately after the instruction selection due to the incomplete
+  ; PHI node in an MBB whose incoming values were never codegenerated.
+  ;
+  ; GCN-LABEL: name: test
+  ; GCN: bb.{{[0-9]+}}.entry:
+  ; GCN: bb.{{[0-9]+}}.entry.true.blk:
+  ; GCN: bb.{{[0-9]+}}.entry.false.blk:
+  ; GCN: bb.{{[0-9]+}}.switch.blk:
+
+  ; GCN-NOT: bb.{{[0-9]+}}.preheader.blk
+  ; GCN-NOT: bb.{{[0-9]+}}.pre.false.blk:
+  ; GCN-NOT: bb.{{[0-9]+}}.unreach.blk:
+  ; GCN-NOT: PHI
+
+  ; GCN: bb.{{[0-9]+}}.exit:
+  entry:
+    %idx = tail call i32 @llvm.amdgcn.workitem.id.x() #0
+    br i1 undef, label %entry.true.blk, label %entry.false.blk
+
+  entry.true.blk:                                   ; preds = %entry
+    %exit.cmp = icmp ult i32 %idx, 3
+    br i1 %exit.cmp, label %switch.blk, label %exit
+
+  entry.false.blk:                                  ; preds = %entry
+    unreachable
+
+  switch.blk:                                       ; preds = %entry.true.blk
+    switch i32 %idx, label %preheader.blk [
+      i32 0, label %exit
+      i32 1, label %exit
+      i32 2, label %exit
+    ]
+
+  preheader.blk:                                    ; preds = %switch.blk
+    %pre.exit = icmp ult i32 %idx, 5
+    br i1 %pre.exit, label %unreach.blk, label %pre.false.blk
+
+  pre.false.blk:                                    ; preds = %preheader.blk
+    %call.pre.false = tail call i32 @func(i32 %idx) #0
+    br label %unreach.blk
+
+  unreach.blk:                                      ; preds = %preheader.blk, %pre.false.blk
+    %phi.val = phi i32 [ %call.pre.false, %pre.false.blk ], [ undef, %preheader.blk ]
+    store i32 %phi.val, i32* undef
+    unreachable
+
+  exit:                                             ; preds = %switch.blk
+    ret void
+}
+
+declare i32 @llvm.amdgcn.workitem.id.x() #0
+declare i32 @func(i32)#0
+
+attributes #0 = { nounwind readnone }
+attributes #1 = { nounwind }
Index: llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
@@ -787,10 +787,14 @@
 
   if (EnableLoadStoreVectorizer)
     addPass(createLoadStoreVectorizerPass());
+
+  // Moved it from PreISel so that any unreachable blocks
+  // introduced during the transformation will be removed by
+  // the UnreachableBlockElim pass.
+  addPass(createLowerSwitchPass());
 }
 
 bool AMDGPUPassConfig::addPreISel() {
-  addPass(createLowerSwitchPass());
   addPass(createFlattenCFGPass());
   return false;
 }


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