commit d8b079708da672c99529b213cb3be7fea6a86830
author Benjamin Kramer <benny.kra@googlemail.com> Sat Oct 15 13:15:05 2016 +0000
committer Benjamin Kramer <benny.kra@googlemail.com> Sat Oct 15 13:15:05 2016 +0000
tree e6f790f209f19efd92346bf7c076677bcb89d525
parent 4b5e24df9a8559dec580c01439df6082e15ad277

[SimplifyCFG] Use the error checking provided by getPrevNode.

BasicBlock::size is O(insts), making this loop O(blocks*insts), which
can be really slow on generated code. getPrevNode already checks if
we're at the beginning of the block and returns nullptr if so, just use
that instead. No functionality change intended.

llvm-svn: 284303

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index a45a0c7..21bb87b 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1584,12 +1584,15 @@
       Fail = false;
       Insts.clear();
       for (auto *BB : Blocks) {
-        if (BB->size() <= 1) {
-          // Block wasn't big enough
-          Fail = true;
-          return;
+        if (Instruction *Terminator = BB->getTerminator()) {
+          if (Instruction *LastNonTerminator = Terminator->getPrevNode()) {
+            Insts.push_back(LastNonTerminator);
+            continue;
+          }
         }
-        Insts.push_back(BB->getTerminator()->getPrevNode());
+        // Block wasn't big enough.
+        Fail = true;
+        return;
       }
     }
 
@@ -1601,11 +1604,12 @@
       if (Fail)
         return;
       for (auto *&Inst : Insts) {
-        if (Inst == &Inst->getParent()->front()) {
+        Inst = Inst->getPrevNode();
+        // Already at beginning of block.
+        if (!Inst) {
           Fail = true;
           return;
         }
-        Inst = Inst->getPrevNode();
       }
     }