[llvm-commits] [llvm] r71609 - in /llvm/trunk: lib/CodeGen/CodePlacementOpt.cpp test/CodeGen/X86/avoid-loop-align-2.ll

[Evan Cheng]

Author: evancheng
Date: Tue May 12 18:58:14 2009
New Revision: 71609

URL: http://llvm.org/viewvc/llvm-project?rev=71609&view=rev
Log:
If header of inner loop is aligned, do not align the outer loop header. We don't want to add nops in the outer loop for the sake of aligning the inner loop.

Added:
    llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll
Modified:
    llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp

Modified: llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp?rev=71609&r1=71608&r2=71609&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp (original)
+++ llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp Tue May 12 18:58:14 2009
@@ -62,6 +62,8 @@
 
   private:
     bool OptimizeIntraLoopEdges();
+    bool HeaderShouldBeAligned(MachineBasicBlock *MBB, MachineLoop *L,
+                               SmallPtrSet<MachineBasicBlock*, 4> &DoNotAlign);
     bool AlignLoops(MachineFunction &MF);
   };
 
@@ -244,14 +246,37 @@
 /// should be aligned. For now, we will not align it if all the predcessors
 /// (i.e. loop back edges) are laid out above the header. FIXME: Do not
 /// align small loops.
-static bool HeaderShouldBeAligned(MachineBasicBlock *MBB) {
+bool
+CodePlacementOpt::HeaderShouldBeAligned(MachineBasicBlock *MBB, MachineLoop *L,
+                               SmallPtrSet<MachineBasicBlock*, 4> &DoNotAlign) {
+  if (DoNotAlign.count(MBB))
+    return false;
+
+  bool BackEdgeBelow = false;
   for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
          PE = MBB->pred_end(); PI != PE; ++PI) {
     MachineBasicBlock *PredMBB = *PI;
-    if (PredMBB == MBB || PredMBB->getNumber() > MBB->getNumber())
-      return true;
+    if (PredMBB == MBB || PredMBB->getNumber() > MBB->getNumber()) {
+      BackEdgeBelow = true;
+      break;
+    }
+  }
+
+  if (!BackEdgeBelow)
+    return false;
+
+  // Ok, we are going to align this loop header. If it's an inner loop,
+  // do not align its outer loop.
+  MachineBasicBlock *PreHeader = L->getLoopPreheader();
+  if (PreHeader) {
+    MachineLoop *L = MLI->getLoopFor(PreHeader);
+    if (L) {
+      MachineBasicBlock *HeaderBlock = L->getHeader();
+      HeaderBlock->setAlignment(0);
+      DoNotAlign.insert(HeaderBlock);
+    }
   }
-  return false;
+  return true;
 }
 
 /// AlignLoops - Align loop headers to target preferred alignments.
@@ -269,14 +294,16 @@
   MF.RenumberBlocks();
 
   bool Changed = false;
+  SmallPtrSet<MachineBasicBlock*, 4> DoNotAlign;
   for (unsigned i = 0, e = LoopHeaders.size(); i != e; ++i) {
     MachineBasicBlock *HeaderMBB = LoopHeaders[i];
     MachineBasicBlock *PredMBB = prior(MachineFunction::iterator(HeaderMBB));
-    if (MLI->getLoopFor(HeaderMBB) == MLI->getLoopFor(PredMBB))
+    MachineLoop *L = MLI->getLoopFor(HeaderMBB);
+    if (L == MLI->getLoopFor(PredMBB))
       // If previously BB is in the same loop, don't align this BB. We want
       // to prevent adding noop's inside a loop.
       continue;
-    if (HeaderShouldBeAligned(HeaderMBB)) {
+    if (HeaderShouldBeAligned(HeaderMBB, L, DoNotAlign)) {
       HeaderMBB->setAlignment(Align);
       Changed = true;
       ++NumHeaderAligned;

Added: llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll?rev=71609&view=auto

==============================================================================
--- llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll (added)
+++ llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll Tue May 12 18:58:14 2009
@@ -0,0 +1,45 @@
+; RUN: llvm-as < %s | llc -march=x86 | grep align | count 3
+
+ at x = external global i32*		; <i32**> [#uses=1]
+
+define i32 @t(i32 %a, i32 %b) nounwind readonly ssp {
+entry:
+	%0 = icmp eq i32 %a, 0		; <i1> [#uses=1]
+	br i1 %0, label %bb5, label %bb.nph12
+
+bb.nph12:		; preds = %entry
+	%1 = icmp eq i32 %b, 0		; <i1> [#uses=1]
+	%2 = load i32** @x, align 8		; <i32*> [#uses=1]
+	br i1 %1, label %bb2.preheader, label %bb2.preheader.us
+
+bb2.preheader.us:		; preds = %bb2.bb3_crit_edge.us, %bb.nph12
+	%indvar18 = phi i32 [ 0, %bb.nph12 ], [ %indvar.next19, %bb2.bb3_crit_edge.us ]		; <i32> [#uses=2]
+	%sum.111.us = phi i32 [ 0, %bb.nph12 ], [ %4, %bb2.bb3_crit_edge.us ]		; <i32> [#uses=0]
+	%tmp16 = mul i32 %indvar18, %a		; <i32> [#uses=1]
+	br label %bb1.us
+
+bb1.us:		; preds = %bb1.us, %bb2.preheader.us
+	%indvar = phi i32 [ 0, %bb2.preheader.us ], [ %indvar.next, %bb1.us ]		; <i32> [#uses=2]
+	%tmp17 = add i32 %indvar, %tmp16		; <i32> [#uses=1]
+	%tmp. = zext i32 %tmp17 to i64		; <i64> [#uses=1]
+	%3 = getelementptr i32* %2, i64 %tmp.		; <i32*> [#uses=1]
+	%4 = load i32* %3, align 4		; <i32> [#uses=2]
+	%indvar.next = add i32 %indvar, 1		; <i32> [#uses=2]
+	%exitcond = icmp eq i32 %indvar.next, %b		; <i1> [#uses=1]
+	br i1 %exitcond, label %bb2.bb3_crit_edge.us, label %bb1.us
+
+bb2.bb3_crit_edge.us:		; preds = %bb1.us
+	%indvar.next19 = add i32 %indvar18, 1		; <i32> [#uses=2]
+	%exitcond22 = icmp eq i32 %indvar.next19, %a		; <i1> [#uses=1]
+	br i1 %exitcond22, label %bb5, label %bb2.preheader.us
+
+bb2.preheader:		; preds = %bb2.preheader, %bb.nph12
+	%indvar24 = phi i32 [ %indvar.next25, %bb2.preheader ], [ 0, %bb.nph12 ]		; <i32> [#uses=1]
+	%indvar.next25 = add i32 %indvar24, 1		; <i32> [#uses=2]
+	%exitcond28 = icmp eq i32 %indvar.next25, %a		; <i1> [#uses=1]
+	br i1 %exitcond28, label %bb5, label %bb2.preheader
+
+bb5:		; preds = %bb2.preheader, %bb2.bb3_crit_edge.us, %entry
+	%sum.1.lcssa = phi i32 [ 0, %entry ], [ 0, %bb2.preheader ], [ %4, %bb2.bb3_crit_edge.us ]		; <i32> [#uses=1]
+	ret i32 %sum.1.lcssa
+}