From 279c22e6da2612f024b70e5509ffb0cad32f38b2 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Tue, 21 Oct 2008 03:29:32 +0000
Subject: Optimized FCMP_OEQ and FCMP_UNE for x86.

Where previously LLVM might emit code like this:

        ucomisd %xmm1, %xmm0
        setne   %al
        setp    %cl
        orb     %al, %cl
        jne     .LBB4_2

it now emits this:

        ucomisd %xmm1, %xmm0
        jne     .LBB4_2
        jp      .LBB4_2

It has fewer instructions and uses fewer registers, but it does
have more branches. And in the case that this code is followed by
a non-fallthrough edge, it may be followed by a jmp instruction,
resulting in three branch instructions in sequence. Some effort
is made to avoid this situation.

To achieve this, X86ISelLowering.cpp now recognizes FCMP_OEQ and
FCMP_UNE in lowered form, and replace them with code that emits
two branches, except in the case where it would require converting
a fall-through edge to an explicit branch.

Also, X86InstrInfo.cpp's branch analysis and transform code now
knows now to handle blocks with multiple conditional branches. It
uses loops instead of having fixed checks for up to two
instructions. It can now analyze and transform code generated
from FCMP_OEQ and FCMP_UNE.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57873 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/IfConversion.cpp | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

(limited to 'lib/CodeGen/IfConversion.cpp')

diff --git a/lib/CodeGen/IfConversion.cpp b/lib/CodeGen/IfConversion.cpp
index 38fce9b..a83d7f1 100644
--- a/lib/CodeGen/IfConversion.cpp
+++ b/lib/CodeGen/IfConversion.cpp
@@ -849,7 +849,8 @@ bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
   }
 
   if (Kind == ICSimpleFalse)
-    TII->ReverseBranchCondition(Cond);
+    if (TII->ReverseBranchCondition(Cond))
+      assert(false && "Unable to reverse branch condition!");
 
   if (CvtBBI->BB->pred_size() > 1) {
     BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
@@ -914,21 +915,23 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
   }
 
   if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
-    TII->ReverseBranchCondition(Cond);
+    if (TII->ReverseBranchCondition(Cond))
+      assert(false && "Unable to reverse branch condition!");
 
   if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
-    ReverseBranchCondition(*CvtBBI);
-    // BB has been changed, modify its predecessors (except for this
-    // one) so they don't get ifcvt'ed based on bad intel.
-    for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
-           E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
-      MachineBasicBlock *PBB = *PI;
-      if (PBB == BBI.BB)
-        continue;
-      BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
-      if (PBBI.IsEnqueued) {
-        PBBI.IsAnalyzed = false;
-        PBBI.IsEnqueued = false;
+    if (ReverseBranchCondition(*CvtBBI)) {
+      // BB has been changed, modify its predecessors (except for this
+      // one) so they don't get ifcvt'ed based on bad intel.
+      for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
+             E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
+        MachineBasicBlock *PBB = *PI;
+        if (PBB == BBI.BB)
+          continue;
+        BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
+        if (PBBI.IsEnqueued) {
+          PBBI.IsAnalyzed = false;
+          PBBI.IsEnqueued = false;
+        }
       }
     }
   }
@@ -1028,7 +1031,8 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
   BBInfo *BBI1 = &TrueBBI;
   BBInfo *BBI2 = &FalseBBI;
   SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
-  TII->ReverseBranchCondition(RevCond);
+  if (TII->ReverseBranchCondition(RevCond))
+    assert(false && "Unable to reverse branch condition!");
   SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
   SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
 
-- 
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