[llvm-commits] [llvm] r129634 - /llvm/trunk/lib/Target/ARM/ARMFastISel.cpp

[Stuart Hastings]

Author: stuart
Date: Fri Apr 15 22:31:26 2011
New Revision: 129634

URL: http://llvm.org/viewvc/llvm-project?rev=129634&view=rev
Log:
Correct result when a branch condition is live across a block
boundary.  <rdar://problem/8933028>

Modified:
    llvm/trunk/lib/Target/ARM/ARMFastISel.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMFastISel.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMFastISel.cpp?rev=129634&r1=129633&r2=129634&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMFastISel.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMFastISel.cpp Fri Apr 15 22:31:26 2011
@@ -1121,10 +1121,16 @@
   unsigned CmpReg = getRegForValue(BI->getCondition());
   if (CmpReg == 0) return false;
 
-  // Re-set the flags just in case.
-  unsigned CmpOpc = isThumb ? ARM::t2CMPri : ARM::CMPri;
-  AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, TII.get(CmpOpc))
-                  .addReg(CmpReg).addImm(0));
+  // We've been divorced from our compare!  Our block was split, and
+  // now our compare lives in a predecessor block.  We musn't
+  // re-compare here, as the children of the compare aren't guaranteed
+  // live across the block boundary (we *could* check for this).
+  // Regardless, the compare has been done in the predecessor block,
+  // and it left a value for us in a virtual register.  Ergo, we test
+  // the one-bit value left in the virtual register.
+  unsigned TstOpc = isThumb ? ARM::t2TSTri : ARM::TSTri;
+  AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, TII.get(TstOpc))
+                  .addReg(CmpReg).addImm(1));
 
   unsigned BrOpc = isThumb ? ARM::t2Bcc : ARM::Bcc;
   BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, TII.get(BrOpc))