MC: Stop restarting layout on every relaxation.
- Still O(N^2), just a faster form, and now its the MCAsmLayout's fault.
On the .s I am tuning against (combine.s from 403.gcc):
--
ddunbar@lordcrumb:MC$ diff stats-before.txt stats-after.txt
5,10c5,10
< 1728 assembler - Number of assembler layout and relaxation steps
< 7707 assembler - Number of emitted assembler fragments
< 120588 assembler - Number of emitted object file bytes
< 2233448 assembler - Number of evaluated fixups
< 1727 assembler - Number of relaxed instructions
< 6723845 mcexpr - Number of MCExpr evaluations
---
> 3 assembler - Number of assembler layout and relaxation steps
> 7707 assembler - Number of emitted assembler fragments
> 120588 assembler - Number of emitted object file bytes
> 14796 assembler - Number of evaluated fixups
> 1727 assembler - Number of relaxed instructions
> 67889 mcexpr - Number of MCExpr evaluations
--
Feel free to LOL at the -before numbers, if you like.
I am a little surprised we make more than 2 relaxation passes. It's pretty
trivial for us to do relaxation out-of-order if that would give a speedup.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99543 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index c3e2ca8..79a8436 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -45,6 +45,39 @@
/* *** */
+void MCAsmLayout::UpdateForSlide(MCFragment *F, int SlideAmount) {
+ // We shouldn't have to do anything special to support negative slides, and it
+ // is a perfectly valid thing to do as long as other parts of the system are
+ // can guarantee convergence.
+ assert(SlideAmount >= 0 && "Negative slides not yet supported");
+
+ // Update the layout by simply recomputing the layout for the entire
+ // file. This is trivially correct, but very slow.
+ //
+ // FIXME-PERF: This is O(N^2), but will be eliminated once we get smarter.
+
+ // Layout the concrete sections and fragments.
+ MCAssembler &Asm = getAssembler();
+ uint64_t Address = 0;
+ for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
+ // Skip virtual sections.
+ if (Asm.getBackend().isVirtualSection(it->getSection()))
+ continue;
+
+ // Layout the section fragments and its size.
+ Address = Asm.LayoutSection(*it, *this, Address);
+ }
+
+ // Layout the virtual sections.
+ for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
+ if (!Asm.getBackend().isVirtualSection(it->getSection()))
+ continue;
+
+ // Layout the section fragments and its size.
+ Address = Asm.LayoutSection(*it, *this, Address);
+ }
+}
+
uint64_t MCAsmLayout::getFragmentAddress(const MCFragment *F) const {
assert(F->getParent() && "Missing section()!");
return getSectionAddress(F->getParent()) + getFragmentOffset(F);
@@ -716,6 +749,7 @@
}
// Scan for fragments that need relaxation.
+ bool WasRelaxed = false;
for (iterator it = begin(), ie = end(); it != ie; ++it) {
MCSectionData &SD = *it;
@@ -747,6 +781,7 @@
VecOS.flush();
// Update the instruction fragment.
+ int SlideAmount = Code.size() - IF->getInstSize();
IF->setInst(Relaxed);
IF->getCode() = Code;
IF->getFixups().clear();
@@ -756,15 +791,13 @@
F.getKind()));
}
- // Restart layout.
- //
- // FIXME-PERF: This is O(N^2), but will be eliminated once we have a
- // smart MCAsmLayout object.
- return true;
+ // Update the layout, and remember that we relaxed.
+ Layout.UpdateForSlide(IF, SlideAmount);
+ WasRelaxed = true;
}
}
- return false;
+ return WasRelaxed;
}
void MCAssembler::FinishLayout(MCAsmLayout &Layout) {