Merge memsets followed by neighboring memsets and other stores into

larger memsets.  Among other things, this fixes rdar://8760394 and
allows us to handle "Example 2" from http://blog.regehr.org/archives/320,
compiling it into a single 4096-byte memset:

_mad_synth_mute:                        ## @mad_synth_mute
## BB#0:                                ## %entry
	pushq	%rax
	movl	$4096, %esi             ## imm = 0x1000
	callq	___bzero
	popq	%rax
	ret



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123089 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 18 insertions, 3 deletions

diff --git a/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index c2844375c4..4210f0d9b7 100644
--- a/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -322,6 +322,7 @@ namespace {
   
     // Helper fuctions
     bool processStore(StoreInst *SI, BasicBlock::iterator &BBI);
+    bool processMemSet(MemSetInst *SI, BasicBlock::iterator &BBI);
     bool processMemCpy(MemCpyInst *M);
     bool processMemMove(MemMoveInst *M);
     bool performCallSlotOptzn(Instruction *cpy, Value *cpyDst, Value *cpySrc,
@@ -511,6 +512,17 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
   return false;
 }
 
+bool MemCpyOpt::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) {
+  // See if there is another memset or store neighboring this memset which
+  // allows us to widen out the memset to do a single larger store.
+  if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(),
+                                            MSI->getValue())) {
+    BBI = I;  // Don't invalidate iterator.
+    return true;
+  }
+  return false;
+}
+
 
 /// performCallSlotOptzn - takes a memcpy and a call that it depends on,
 /// and checks for the possibility of a call slot optimization by having
@@ -775,6 +787,7 @@ bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
       return true;
     }
   }
+  
   return false;
 }
 
@@ -884,11 +897,13 @@ bool MemCpyOpt::iterateOnFunction(Function &F) {
       
       if (StoreInst *SI = dyn_cast<StoreInst>(I))
         MadeChange |= processStore(SI, BI);
-      else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I)) {
+      else if (MemSetInst *M = dyn_cast<MemSetInst>(I))
+        RepeatInstruction = processMemSet(M, BI);
+      else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I))
         RepeatInstruction = processMemCpy(M);
-      } else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I)) {
+      else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I))
         RepeatInstruction = processMemMove(M);
-      } else if (CallSite CS = (Value*)I) {
+      else if (CallSite CS = (Value*)I) {
         for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
           if (CS.paramHasAttr(i+1, Attribute::ByVal))
             MadeChange |= processByValArgument(CS, i);