69 lines
2.7 KiB
Plaintext
69 lines
2.7 KiB
Plaintext
- Use int3 trap padding between functions instead of trapsleds with a leading jump.
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- Emit trap alignment between basic blocks that are unreachable via
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fallthrough. Avoids unnecessary jmp instructions in the middle
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of functions and makes disassembly nicer to read.
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Index: lib/CodeGen/AsmPrinter/AsmPrinter.cpp
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--- lib/CodeGen/AsmPrinter/AsmPrinter.cpp.orig
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+++ lib/CodeGen/AsmPrinter/AsmPrinter.cpp
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@@ -745,7 +745,7 @@ void AsmPrinter::emitFunctionHeader() {
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emitLinkage(&F, CurrentFnSym);
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if (MAI->hasFunctionAlignment())
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- emitAlignment(MF->getAlignment(), &F);
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+ emitTrapAlignment(MF->getAlignment(), &F);
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if (MAI->hasDotTypeDotSizeDirective())
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OutStreamer->emitSymbolAttribute(CurrentFnSym, MCSA_ELF_TypeFunction);
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@@ -2462,6 +2462,30 @@ void AsmPrinter::emitAlignment(Align Alignment, const
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}
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//===----------------------------------------------------------------------===//
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+/// emitTrapAlignment - Emit an alignment directive to the specified power of
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+/// two boundary, but call emitTrapToAlignment to fill with Trap instructions
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+/// if the Target implements emitTrapToAlignment.
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+void AsmPrinter::emitTrapAlignment(Align Alignment, const GlobalObject *GV) const {
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+ if (GV)
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+ Alignment = getGVAlignment(GV, GV->getParent()->getDataLayout(), Alignment);
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+
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+ if (Alignment == Align(1)) return; // 1-byte aligned: no need to emit alignment.
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+
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+ emitTrapToAlignment(Alignment);
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+}
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+
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+//===----------------------------------------------------------------------===//
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+/// emitTrapToAlignment - Emit an alignment directive to the specified power
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+/// of two boundary. This default implementation calls EmitCodeAlignment on
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+/// the OutStreamer, but can be overridden by Target implementations.
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+void AsmPrinter::emitTrapToAlignment(Align Alignment) const {
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+ if (Alignment == Align(1)) return;
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+ OutStreamer->emitCodeAlignment(Alignment.value());
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+}
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+
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+
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+
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+//===----------------------------------------------------------------------===//
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// Constant emission.
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//===----------------------------------------------------------------------===//
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@@ -3246,10 +3270,17 @@ void AsmPrinter::emitBasicBlockStart(const MachineBasi
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}
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}
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+ bool isReachableViaFallthrough =
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+ std::find(MBB.pred_begin(), MBB.pred_end(), MBB.getPrevNode()) !=
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+ MBB.pred_end();
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// Emit an alignment directive for this block, if needed.
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const Align Alignment = MBB.getAlignment();
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- if (Alignment != Align(1))
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- emitAlignment(Alignment);
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+ if (Alignment != Align(1)) {
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+ if (isReachableViaFallthrough)
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+ emitAlignment(Alignment);
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+ else
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+ emitTrapAlignment(Alignment);
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+ }
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// Switch to a new section if this basic block must begin a section. The
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// entry block is always placed in the function section and is handled
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