[llvm] 949abf7 - [llvm-readelf, propeller] Add fallthrough bit to basic block metadata in BB-Address-Map section.
Rahman Lavaee via llvm-commits
llvm-commits at lists.llvm.org
Mon Mar 22 21:39:22 PDT 2021
Author: Rahman Lavaee
Date: 2021-03-22T21:38:05-07:00
New Revision: 949abf7d6afb9abd8d35bfb3ca2a1fb2e47a2c79
URL: https://github.com/llvm/llvm-project/commit/949abf7d6afb9abd8d35bfb3ca2a1fb2e47a2c79
DIFF: https://github.com/llvm/llvm-project/commit/949abf7d6afb9abd8d35bfb3ca2a1fb2e47a2c79.diff
LOG: [llvm-readelf, propeller] Add fallthrough bit to basic block metadata in BB-Address-Map section.
This patch adds a fallthrough bit to basic block metadata, indicating whether the basic block can fallthrough without taking any branches. The bit will help us avoid an intel LBR bug which results in occasional duplicate entries at the beginning of the LBR stack.
This patch uses `MachineBasicBlock::canFallThrough()` to set the bit. This is not a const method because it eventually calls `TargetInstrInfo::analyzeBranch`, but it calls this function with the default `AllowModify=false`. So we can either make the argument to the `getBBAddrMapMetadata` non-const, or we can use `const_cast` when calling `canFallThrough`. I decide to go with the latter since this is purely due to legacy code, and in general we should not allow the BasicBlock to be mutable during `getBBAddrMapMetadata`.
Reviewed By: tmsriram
Differential Revision: https://reviews.llvm.org/D96918
Added:
Modified:
llvm/include/llvm/Object/ELFTypes.h
llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
llvm/test/tools/llvm-readobj/ELF/bb-addr-map.test
llvm/tools/llvm-readobj/ELFDumper.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/Object/ELFTypes.h b/llvm/include/llvm/Object/ELFTypes.h
index 32548f1435f7..534deaabed8d 100644
--- a/llvm/include/llvm/Object/ELFTypes.h
+++ b/llvm/include/llvm/Object/ELFTypes.h
@@ -802,13 +802,15 @@ template <class ELFT> struct Elf_BBAddrMap_Impl {
// The following fields are decoded from the Metadata field. The encoding
// happens in AsmPrinter.cpp:getBBAddrMapMetadata.
- bool HasReturn; // If this block ends with a return (or tail call).
- bool HasTailCall; // If this block ends with a tail call.
- bool IsEHPad; // If this is an exception handling block.
+ bool HasReturn; // If this block ends with a return (or tail call).
+ bool HasTailCall; // If this block ends with a tail call.
+ bool IsEHPad; // If this is an exception handling block.
+ bool CanFallThrough; // If this block can fall through to its next.
BBEntry(uint32_t Offset, uint32_t Size, uint32_t Metadata)
: Offset(Offset), Size(Size), HasReturn(Metadata & 1),
- HasTailCall(Metadata & (1 << 1)), IsEHPad(Metadata & (1 << 2)){};
+ HasTailCall(Metadata & (1 << 1)), IsEHPad(Metadata & (1 << 2)),
+ CanFallThrough(Metadata & (1 << 3)){};
};
std::vector<BBEntry> BBEntries; // Basic block entries for this function.
};
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index fc0b278325d9..160eaefeaf90 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1078,17 +1078,19 @@ void AsmPrinter::emitFrameAlloc(const MachineInstr &MI) {
/// Returns the BB metadata to be emitted in the .llvm_bb_addr_map section for a
/// given basic block. This can be used to capture more precise profile
-/// information. We use the last 3 bits (LSBs) to ecnode the following
+/// information. We use the last 4 bits (LSBs) to encode the following
/// information:
/// * (1): set if return block (ret or tail call).
/// * (2): set if ends with a tail call.
/// * (3): set if exception handling (EH) landing pad.
+/// * (4): set if the block can fall through to its next.
/// The remaining bits are zero.
static unsigned getBBAddrMapMetadata(const MachineBasicBlock &MBB) {
const TargetInstrInfo *TII = MBB.getParent()->getSubtarget().getInstrInfo();
return ((unsigned)MBB.isReturnBlock()) |
((!MBB.empty() && TII->isTailCall(MBB.back())) << 1) |
- (MBB.isEHPad() << 2);
+ (MBB.isEHPad() << 2) |
+ (const_cast<MachineBasicBlock &>(MBB).canFallThrough() << 3);
}
void AsmPrinter::emitBBAddrMapSection(const MachineFunction &MF) {
diff --git a/llvm/test/tools/llvm-readobj/ELF/bb-addr-map.test b/llvm/test/tools/llvm-readobj/ELF/bb-addr-map.test
index f9b9dc0980e5..0cebfee6872a 100644
--- a/llvm/test/tools/llvm-readobj/ELF/bb-addr-map.test
+++ b/llvm/test/tools/llvm-readobj/ELF/bb-addr-map.test
@@ -24,6 +24,7 @@
# LLVM-NEXT: HasReturn: No
# LLVM-NEXT: HasTailCall: Yes
# LLVM-NEXT: IsEHPad: No
+# LLVM-NEXT: CanFallThrough: No
# LLVM-NEXT: }
# LLVM-NEXT: {
# LLVM-NEXT: Offset: 0x3
@@ -31,6 +32,7 @@
# LLVM-NEXT: HasReturn: Yes
# LLVM-NEXT: HasTailCall: No
# LLVM-NEXT: IsEHPad: Yes
+# LLVM-NEXT: CanFallThrough: No
# LLVM-NEXT: }
# LLVM-NEXT: ]
# LLVM-NEXT: }
@@ -43,6 +45,7 @@
# LLVM-NEXT: HasReturn: No
# LLVM-NEXT: HasTailCall: No
# LLVM-NEXT: IsEHPad: No
+# LLVM-NEXT: CanFallThrough: Yes
# LLVM-NEXT: }
# LLVM-NEXT: ]
# LLVM-NEXT: }
@@ -57,6 +60,7 @@
# LLVM-NEXT: HasReturn: Yes
# LLVM-NEXT: HasTailCall: Yes
# LLVM-NEXT: IsEHPad: No
+# LLVM-NEXT: CanFallThrough: Yes
# LLVM-NEXT: }
# LLVM-NEXT: ]
# LLVM-NEXT: }
@@ -78,6 +82,7 @@
# TRUNCATED-NEXT: HasReturn: Yes
# TRUNCATED-NEXT: HasTailCall: Yes
# TRUNCATED-NEXT: IsEHPad: No
+# TRUNCATED-NEXT: CanFallThrough: Yes
# TRUNCATED-NEXT: }
# TRUNCATED-NEXT: ]
# TRUNCATED-NEXT: }
diff --git a/llvm/tools/llvm-readobj/ELFDumper.cpp b/llvm/tools/llvm-readobj/ELFDumper.cpp
index c4938ad7b5f1..20d4c42f1b18 100644
--- a/llvm/tools/llvm-readobj/ELFDumper.cpp
+++ b/llvm/tools/llvm-readobj/ELFDumper.cpp
@@ -6528,6 +6528,7 @@ template <class ELFT> void LLVMELFDumper<ELFT>::printBBAddrMaps() {
W.printBoolean("HasReturn", BBE.HasReturn);
W.printBoolean("HasTailCall", BBE.HasTailCall);
W.printBoolean("IsEHPad", BBE.IsEHPad);
+ W.printBoolean("CanFallThrough", BBE.CanFallThrough);
}
}
}
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