Add the align_to_end option to .bundle_lock in the MC implementation of aligned
bundling. The document describing this feature and the implementation has also
been updated:
https://sites.google.com/a/chromium.org/dev/nativeclient/pnacl/aligned-bundling-support-in-llvm
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171797 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index 20b64e2..d30dc7d 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -167,10 +167,34 @@
"computeBundlePadding should only be called if bundling is enabled");
uint64_t BundleMask = BundleSize - 1;
uint64_t OffsetInBundle = FOffset & BundleMask;
+ uint64_t EndOfFragment = OffsetInBundle + FSize;
- // If the fragment would cross a bundle boundary, add enough padding until
- // the end of the current bundle.
- if (OffsetInBundle + FSize > BundleSize)
+ // There are two kinds of bundling restrictions:
+ //
+ // 1) For alignToBundleEnd(), add padding to ensure that the fragment will
+ // *end* on a bundle boundary.
+ // 2) Otherwise, check if the fragment would cross a bundle boundary. If it
+ // would, add padding until the end of the bundle so that the fragment
+ // will start in a new one.
+ if (F->alignToBundleEnd()) {
+ // Three possibilities here:
+ //
+ // A) The fragment just happens to end at a bundle boundary, so we're good.
+ // B) The fragment ends before the current bundle boundary: pad it just
+ // enough to reach the boundary.
+ // C) The fragment ends after the current bundle boundary: pad it until it
+ // reaches the end of the next bundle boundary.
+ //
+ // Note: this code could be made shorter with some modulo trickery, but it's
+ // intentionally kept in its more explicit form for simplicity.
+ if (EndOfFragment == BundleSize)
+ return 0;
+ else if (EndOfFragment < BundleSize)
+ return BundleSize - EndOfFragment;
+ else { // EndOfFragment > BundleSize
+ return 2 * BundleSize - EndOfFragment;
+ }
+ } else if (EndOfFragment > BundleSize)
return BundleSize - OffsetInBundle;
else
return 0;
@@ -204,7 +228,7 @@
: Section(&_Section),
Ordinal(~UINT32_C(0)),
Alignment(1),
- BundleLocked(false), BundleGroupBeforeFirstInst(false),
+ BundleLockState(NotBundleLocked), BundleGroupBeforeFirstInst(false),
HasInstructions(false)
{
if (A)