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).
llvm-svn: 307920
diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index 3d57acf..93eab68 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -2026,6 +2026,24 @@
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())
diff --git a/llvm/test/Transforms/GlobalOpt/pr33686.ll b/llvm/test/Transforms/GlobalOpt/pr33686.ll
new file mode 100644
index 0000000..153a85f
--- /dev/null
+++ b/llvm/test/Transforms/GlobalOpt/pr33686.ll
@@ -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: }
+
+@glob = external global i16, align 1
+
+define void @beth() {
+entry:
+ ret void
+
+notreachable:
+ %patatino = select i1 undef, i16* @glob, i16* %patatino
+ br label %notreachable
+}