From: Evan Cheng <evan.cheng@apple.com>
Date: Thu, 27 Nov 2008 01:16:00 +0000 (+0000)
Subject: Avoid inserting noop's in the middle of a loop.
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=df90841690c4c1c30aa9ea8cfd37c429bb1e9d0b;p=oota-llvm.git

Avoid inserting noop's in the middle of a loop.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60141 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/LoopAligner.cpp b/lib/CodeGen/LoopAligner.cpp
index b8d00595d8a..b67f5c3bf91 100644
--- a/lib/CodeGen/LoopAligner.cpp
+++ b/lib/CodeGen/LoopAligner.cpp
@@ -64,8 +64,14 @@ bool LoopAligner::runOnMachineFunction(MachineFunction &MF) {
 
   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
     MachineBasicBlock *MBB = I;
-    if (MLI->isLoopHeader(MBB))
+    if (MLI->isLoopHeader(MBB)) {
+      MachineBasicBlock *PredBB = prior(I);
+      if (MLI->getLoopFor(MBB) == MLI->getLoopFor(PredBB))
+        // If previously BB is in the same loop, don't align this BB. We want
+        // to prevent adding noop's inside a loop.
+        continue;
       MBB->setAlignment(Align);
+    }
   }
 
   return true;
diff --git a/test/CodeGen/X86/avoid-loop-align.ll b/test/CodeGen/X86/avoid-loop-align.ll
new file mode 100644
index 00000000000..dfc58181d90
--- /dev/null
+++ b/test/CodeGen/X86/avoid-loop-align.ll
@@ -0,0 +1,32 @@
+; RUN: llvm-as < %s | llc -mtriple=i386-apple-darwin | grep align | count 1
+
+@A = common global [100 x i32] zeroinitializer, align 32		; <[100 x i32]*> [#uses=1]
+
+define i8* @test(i8* %Q, i32* %L) nounwind {
+entry:
+	%tmp = tail call i32 (...)* @foo() nounwind		; <i32> [#uses=2]
+	%tmp1 = inttoptr i32 %tmp to i8*		; <i8*> [#uses=1]
+	br label %bb1
+
+bb:		; preds = %bb1, %bb1
+	%indvar.next = add i32 %P.0.rec, 1		; <i32> [#uses=1]
+	br label %bb1
+
+bb1:		; preds = %bb, %entry
+	%P.0.rec = phi i32 [ 0, %entry ], [ %indvar.next, %bb ]		; <i32> [#uses=2]
+	%P.0 = getelementptr i8* %tmp1, i32 %P.0.rec		; <i8*> [#uses=3]
+	%tmp2 = load i8* %P.0, align 1		; <i8> [#uses=1]
+	switch i8 %tmp2, label %bb4 [
+		i8 12, label %bb
+		i8 42, label %bb
+	]
+
+bb4:		; preds = %bb1
+	%tmp3 = ptrtoint i8* %P.0 to i32		; <i32> [#uses=1]
+	%tmp4 = sub i32 %tmp3, %tmp		; <i32> [#uses=1]
+	%tmp5 = getelementptr [100 x i32]* @A, i32 0, i32 %tmp4		; <i32*> [#uses=1]
+	store i32 4, i32* %tmp5, align 4
+	ret i8* %P.0
+}
+
+declare i32 @foo(...)