From: Bill Wendling <isanbard@gmail.com>
Date: Fri, 20 Jan 2012 00:53:28 +0000 (+0000)
Subject: When lowering the 'resume' instruction, look to see if we can eliminate the
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=b618ea5ff97182381107ab6bf52b0c2d8f783d7d;p=oota-llvm.git

When lowering the 'resume' instruction, look to see if we can eliminate the
'insertvalue' instructions that recreate the structure returned by the
'landingpad' instruction. Because the 'insertvalue' instruction isn't supported
by FastISel, this can save a bit of time during -O0 compilation.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148520 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/DwarfEHPrepare.cpp b/lib/CodeGen/DwarfEHPrepare.cpp
index aa442233e5c..f2b29772751 100644
--- a/lib/CodeGen/DwarfEHPrepare.cpp
+++ b/lib/CodeGen/DwarfEHPrepare.cpp
@@ -101,10 +101,40 @@ bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
          I = Resumes.begin(), E = Resumes.end(); I != E; ++I) {
     ResumeInst *RI = *I;
     BranchInst::Create(UnwindBB, RI->getParent());
-    ExtractValueInst *ExnObj = ExtractValueInst::Create(RI->getOperand(0),
-                                                        0, "exn.obj", RI);
+
+    Value *V = RI->getOperand(0);
+    Instruction *ExnObj = 0;
+    InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
+    LoadInst *SelLoad = 0;
+    InsertValueInst *ExcIVI = 0;
+    bool EraseIVIs = false;
+    if (SelIVI) {
+      if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
+        ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0));
+        if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) &&
+            ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
+          ExnObj = cast<Instruction>(ExcIVI->getOperand(1));
+          SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
+          EraseIVIs = true;
+        }
+      }
+    }
+
+    if (!ExnObj)
+      ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
+
     PN->addIncoming(ExnObj, RI->getParent());
     RI->eraseFromParent();
+
+    if (EraseIVIs) {
+      if (SelIVI->getNumUses() == 0)
+        SelIVI->eraseFromParent();
+      if (ExcIVI->getNumUses() == 0)
+        ExcIVI->eraseFromParent();
+      if (SelLoad && SelLoad->getNumUses() == 0)
+        SelLoad->eraseFromParent();
+    }
+
     ++NumResumesLowered;
   }