[llvm] r196845 - Transforms: Don't create bad branch weights when folding a switch

[Justin Bogner]

Author: bogner
Date: Mon Dec  9 18:13:41 2013
New Revision: 196845

URL: http://llvm.org/viewvc/llvm-project?rev=196845&view=rev
Log:
Transforms: Don't create bad branch weights when folding a switch

This avoids creating branch weight metadata of length one when we fold
cases into the default of a switch instruction, which was triggering
an assert.

Modified:
    llvm/trunk/lib/Transforms/Utils/Local.cpp
    llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll

Modified: llvm/trunk/lib/Transforms/Utils/Local.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/Local.cpp?rev=196845&r1=196844&r2=196845&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/Local.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/Local.cpp Mon Dec  9 18:13:41 2013
@@ -127,8 +127,10 @@ bool llvm::ConstantFoldTerminator(BasicB
       // dest.  If so, eliminate it as an explicit compare.
       if (i.getCaseSuccessor() == DefaultDest) {
         MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
-        // MD should have 2 + NumCases operands.
-        if (MD && MD->getNumOperands() == 2 + SI->getNumCases()) {
+        unsigned NCases = SI->getNumCases();
+        // Fold the case metadata into the default if there will be any branches
+        // left, unless the metadata doesn't match the switch.
+        if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
           // Collect branch weights into a vector.
           SmallVector<uint32_t, 8> Weights;
           for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;

Modified: llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll?rev=196845&r1=196844&r2=196845&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll Mon Dec  9 18:13:41 2013
@@ -293,6 +293,23 @@ c:
  ret void
 }
 
+;; test12 - Don't crash if the whole switch is removed
+define void @test12(i32 %M, i32 %N) nounwind uwtable {
+entry:
+  switch i32 %N, label %sw.bb [
+    i32 1, label %sw.bb
+  ], !prof !9
+; CHECK: test12
+; CHECK-NOT: switch
+
+sw.bb:
+  call void @helper(i32 0)
+  br label %sw.epilog
+
+sw.epilog:
+  ret void
+}
+
 !0 = metadata !{metadata !"branch_weights", i32 3, i32 5}
 !1 = metadata !{metadata !"branch_weights", i32 1, i32 1}
 !2 = metadata !{metadata !"branch_weights", i32 1, i32 2}
@@ -302,6 +319,7 @@ c:
 !6 = metadata !{metadata !"branch_weights", i32 1, i32 3}
 !7 = metadata !{metadata !"branch_weights", i32 33, i32 9, i32 8, i32 7}
 !8 = metadata !{metadata !"branch_weights", i32 33, i32 9, i32 8}
+!9 = metadata !{metadata !"branch_weights", i32 7, i32 6}
 
 ; CHECK: !0 = metadata !{metadata !"branch_weights", i32 5, i32 11}
 ; CHECK: !1 = metadata !{metadata !"branch_weights", i32 1, i32 5}