[llvm-commits] [llvm] r145971 - in /llvm/trunk/lib/Target/ARM: ARMBaseInstrInfo.cpp ARMConstantIslandPass.cpp

[Jakob Stoklund Olesen]

Author: stoklund
Date: Tue Dec  6 15:55:39 2011
New Revision: 145971

URL: http://llvm.org/viewvc/llvm-project?rev=145971&view=rev
Log:
Use conservative size estimate for tBR_JTr.

This pseudo-instruction contains a .align directive in its expansion, so
the total size may vary by 2 bytes.

It is too difficult to accurately keep track of this alignment
directive, just use the worst-case size instead.

Modified:
    llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
    llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp?rev=145971&r1=145970&r2=145971&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp Tue Dec  6 15:55:39 2011
@@ -601,12 +601,12 @@
       assert(JTI < JT.size());
       // Thumb instructions are 2 byte aligned, but JT entries are 4 byte
       // 4 aligned. The assembler / linker may add 2 byte padding just before
-      // the JT entries.  The size does not include this padding; the
-      // constant islands pass does separate bookkeeping for it.
+      // the JT entries. The size includes the worst case size of this padding.
       // FIXME: If we know the size of the function is less than (1 << 16) *2
       // bytes, we can use 16-bit entries instead. Then there won't be an
       // alignment issue.
-      unsigned InstSize = (Opc == ARM::tBR_JTr || Opc == ARM::t2BR_JT) ? 2 : 4;
+      // tBR_JT is 2 bytes + 2 bytes worst case padding for table alignment.
+      unsigned InstSize = (Opc == ARM::t2BR_JT) ? 2 : 4;
       unsigned NumEntries = getNumJTEntries(JT, JTI);
       if (Opc == ARM::t2TBB_JT && (NumEntries & 1))
         // Make sure the instruction that follows TBB is 2-byte aligned.

Modified: llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp?rev=145971&r1=145970&r2=145971&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMConstantIslandPass.cpp Tue Dec  6 15:55:39 2011
@@ -525,13 +525,8 @@
           // A Thumb1 table jump may involve padding; for the offsets to
           // be right, functions containing these must be 4-byte aligned.
           // tBR_JTr expands to a mov pc followed by .align 2 and then the jump
-          // table entries. So this code checks whether offset of tBR_JTr + 2
-          // is aligned.  That is held in Offset+MBBSize, which already has
-          // 2 added in for the size of the mov pc instruction.
+          // table entries. GetInstSizeInBytes returns the worst case size.
           MF.EnsureAlignment(2U);
-          if ((Offset+MBBSize)%4 != 0 || HasInlineAsm)
-            // FIXME: Add a pseudo ALIGN instruction instead.
-            MBBSize += 2;           // padding
           continue;   // Does not get an entry in ImmBranches
         case ARM::t2BR_JT:
           T2JumpTables.push_back(I);
@@ -809,23 +804,6 @@
   // Set the size of NewBB in BBSizes.  It does not include any padding now.
   BBSizes[NewBBI] = NewBBSize;
 
-  MachineInstr* ThumbJTMI = prior(NewBB->end());
-  if (ThumbJTMI->getOpcode() == ARM::tBR_JTr) {
-    // We've added another 2-byte instruction before this tablejump, which
-    // means we will always need padding if we didn't before, and vice versa.
-
-    // The original offset of the jump instruction was:
-    unsigned OrigOffset = BBOffsets[OrigBBI] + BBSizes[OrigBBI] - delta;
-    if (OrigOffset%4 == 0) {
-      // We had padding before and now we don't.  No net change in code size.
-      delta = 0;
-    } else {
-      // We didn't have padding before and now we do.
-      BBSizes[NewBBI] += 2;
-      delta = 4;
-    }
-  }
-
   // All BBOffsets following these blocks must be modified.
   if (delta)
     AdjustBBOffsetsAfter(NewBB, delta);