[llvm] r307920 - Reapply [GlobalOpt] Remove unreachable blocks before optimizing a function.

[Davide Italiano via llvm-commits]

Author: davide
Date: Thu Jul 13 08:40:59 2017
New Revision: 307920

URL: http://llvm.org/viewvc/llvm-project?rev=307920&view=rev
Log:
Reapply [GlobalOpt] Remove unreachable blocks before optimizing a function.

This commit reapplies r307215 now that we found out and fixed
the cause of the cfi test failure (in r307871).

Added:
    llvm/trunk/test/Transforms/GlobalOpt/pr33686.ll
Modified:
    llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp

Modified: llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp?rev=307920&r1=307919&r2=307920&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp Thu Jul 13 08:40:59 2017
@@ -2026,6 +2026,24 @@ OptimizeFunctions(Module &M, TargetLibra
       continue;
     }
 
+    // LLVM's definition of dominance allows instructions that are cyclic
+    // in unreachable blocks, e.g.:
+    // %pat = select i1 %condition, @global, i16* %pat
+    // because any instruction dominates an instruction in a block that's
+    // not reachable from entry.
+    // So, remove unreachable blocks from the function, because a) there's
+    // no point in analyzing them and b) GlobalOpt should otherwise grow
+    // some more complicated logic to break these cycles.
+    // Removing unreachable blocks might invalidate the dominator so we
+    // recalculate it.
+    if (!F->isDeclaration()) {
+      if (removeUnreachableBlocks(*F)) {
+        auto &DT = LookupDomTree(*F);
+        DT.recalculate(*F);
+        Changed = true;
+      }
+    }
+
     Changed |= processGlobal(*F, TLI, LookupDomTree);
 
     if (!F->hasLocalLinkage())

Added: llvm/trunk/test/Transforms/GlobalOpt/pr33686.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GlobalOpt/pr33686.ll?rev=307920&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/GlobalOpt/pr33686.ll (added)
+++ llvm/trunk/test/Transforms/GlobalOpt/pr33686.ll Thu Jul 13 08:40:59 2017
@@ -0,0 +1,17 @@
+; RUN: opt -S -globalopt %s | FileCheck %s
+
+; CHECK-LABEL: define void @beth
+; CHECK-NEXT:   entry:
+; CHECK-NEXT:   ret void
+; CHEC-NEXT:  }
+
+ at glob = external global i16, align 1
+
+define void @beth() {
+entry:
+  ret void
+
+notreachable:
+  %patatino = select i1 undef, i16* @glob, i16* %patatino
+  br label %notreachable
+}