[PATCH] D20604: Codegen: Don't tail-duplicate blocks with un-analyzable fallthrough.

[Kyle Butt via llvm-commits]

iteratee updated this revision to Diff 65852.
iteratee added a comment.

Expanded comment.


https://reviews.llvm.org/D20604

Files:
  lib/CodeGen/TailDuplicator.cpp
  test/CodeGen/PowerPC/tail-dup-analyzable-fallthrough.ll

Index: test/CodeGen/PowerPC/tail-dup-analyzable-fallthrough.ll
===================================================================
--- /dev/null
+++ test/CodeGen/PowerPC/tail-dup-analyzable-fallthrough.ll
@@ -0,0 +1,34 @@
+; RUN: llc -O2 < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-n32:64"
+target triple = "powerpc64le-unknown-linux-gnu"
+
+; Check that the conditional return block of fmax_double3.exit was not
+; duplicated into the if.then.i block
+; CHECK: # %if.then.i
+; CHECK: lxvd2x
+; CHECK: stxvd2x
+; CHECK-NOT: bclr
+; CHECK: {{^}}.LBB{{[0-9_]+}}:
+; CHECK-SAME: # %fmax_double3.exit
+; CHECK: bclr
+; CHECK: # %if.then
+; Function Attrs: nounwind
+define void @__fmax_double3_3D_exec(<2 x double>* %input6, i1 %bool1, i1 %bool2) #0 {
+entry:
+  br i1 %bool1, label %if.then.i, label %fmax_double3.exit
+
+if.then.i:                                        ; preds = %entry
+  store <2 x double> zeroinitializer, <2 x double>* %input6, align 32
+  br label %fmax_double3.exit
+
+fmax_double3.exit:                                ; preds = %if.then.i, %entry
+  br i1 %bool2, label %if.then, label %do.end
+
+if.then:                                          ; preds = %fmax_double3.exit
+  unreachable
+
+do.end:                                           ; preds = %fmax_double3.exit
+  ret void
+}
+
+attributes #0 = { nounwind }
Index: lib/CodeGen/TailDuplicator.cpp
===================================================================
--- lib/CodeGen/TailDuplicator.cpp
+++ lib/CodeGen/TailDuplicator.cpp
@@ -591,6 +591,16 @@
     }
   }
 
+  // If the block to be duplicated ends in an unanalyzable fallthrough, don't
+  // duplicate it.
+  // A similar check is necessary in MachineBlockPlacement to make sure pairs of
+  // blocks with unanalyzable fallthrough get layed out contiguously.
+  MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
+  SmallVector<MachineOperand, 4> PredCond;
+  if (TII->analyzeBranch(TailBB, PredTBB, PredFBB, PredCond, true)
+      && TailBB.canFallThrough())
+    return false;
+
   if (HasIndirectbr && PreRegAlloc)
     return true;
 


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