[PATCH] D30556: [IfConversion] Only renormalize probabilities if branches are analyzable

[Krzysztof Parzyszek via Phabricator via llvm-commits]

kparzysz created this revision.

If a block has non-analyzable branches, the listed successors don't need to add up to one. For example, if a block has a conditional tail call, that tail call will not have a corresponding successor in the successor list, but will still be a possible branch.


Repository:
  rL LLVM

https://reviews.llvm.org/D30556

Files:
  lib/CodeGen/IfConversion.cpp
  test/CodeGen/Hexagon/ifcvt-simple-bprob.ll


Index: test/CodeGen/Hexagon/ifcvt-simple-bprob.ll
===================================================================
--- /dev/null
+++ test/CodeGen/Hexagon/ifcvt-simple-bprob.ll
@@ -0,0 +1,36 @@
+; RUN: llc -march=hexagon < %s
+
+; Check that branch probabilities are set correctly after performing the
+; simple variant of if-conversion. The converted block has a branch that
+; is not analyzable.
+
+target triple = "hexagon"
+
+declare void @foo()
+
+; CHECK-LABEL: danny
+; CHECK: if (p0.new) jump:nt foo
+define void @danny(i32 %x) {
+  %t0 = icmp sgt i32 %x, 0
+  br i1 %t0, label %tail, label %exit, !prof !0
+tail:
+  tail call void @foo();
+  ret void
+exit:
+  ret void
+}
+
+; CHECK-LABEL: sammy
+; CHECK: if (!p0.new) jump:t foo
+define void @sammy(i32 %x) {
+  %t0 = icmp sgt i32 %x, 0
+  br i1 %t0, label %exit, label %tail, !prof !0
+tail:
+  tail call void @foo();
+  ret void
+exit:
+  ret void
+}
+
+!0 = !{!"branch_weights", i32 1, i32 2000}
+
Index: lib/CodeGen/IfConversion.cpp
===================================================================
--- lib/CodeGen/IfConversion.cpp
+++ lib/CodeGen/IfConversion.cpp
@@ -2148,7 +2148,8 @@
   // unknown probabilities into known ones.
   // FIXME: This usage is too tricky and in the future we would like to
   // eliminate all unknown probabilities in MBB.
-  ToBBI.BB->normalizeSuccProbs();
+  if (ToBBI.IsBrAnalyzable)
+    ToBBI.BB->normalizeSuccProbs();
 
   SmallVector<MachineBasicBlock *, 4> FromSuccs(FromMBB.succ_begin(),
                                                 FromMBB.succ_end());
@@ -2228,7 +2229,8 @@
 
   // Normalize the probabilities of ToBBI.BB's successors with all adjustment
   // we've done above.
-  ToBBI.BB->normalizeSuccProbs();
+  if (ToBBI.IsBrAnalyzable && FromBBI.IsBrAnalyzable)
+    ToBBI.BB->normalizeSuccProbs();
 
   ToBBI.Predicate.append(FromBBI.Predicate.begin(), FromBBI.Predicate.end());
   FromBBI.Predicate.clear();


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