[ARM] Clear the constant pool cache on explicit .ltorg directives

Multiple ldr pseudoinstructions with the same constant value will
reuse the same constant pool entry. However, if the constant pool
is explicitly flushed with a .ltorg directive, we should not try
to reference constants in the previous pool any longer, since they
may be out of range.

This fixes assembling hand-written assembler source which repeatedly
loads the same constant value, across a binary size larger than the
pc-relative fixup range for ldr instructions (4096 bytes). Such
assembler source already uses explicit .ltorg instructions to emit
constant pools with regular intervals. However if we try to reuse
constants emitted in earlier pools, they end up out of range.

This makes the output of the testcase match what binutils gas does
(prior to this patch, it would fail to assemble).

Differential Revision: https://reviews.llvm.org/D32847

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302416 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/MC/ConstantPools.h b/include/llvm/MC/ConstantPools.h
index c34211c..5d4e32a 100644 (file)
--- a/include/llvm/MC/ConstantPools.h
+++ b/include/llvm/MC/ConstantPools.h
@@ -63,6 +63,8 @@ public:
 
   // Return true if the constant pool is empty
   bool empty();
+
+  void clearCache();
 };
 
 class AssemblerConstantPools {
@@ -86,6 +88,7 @@ class AssemblerConstantPools {
 public:
   void emitAll(MCStreamer &Streamer);
   void emitForCurrentSection(MCStreamer &Streamer);
+  void clearCacheForCurrentSection(MCStreamer &Streamer);
   const MCExpr *addEntry(MCStreamer &Streamer, const MCExpr *Expr,
                          unsigned Size, SMLoc Loc);
 

diff --git a/lib/MC/ConstantPools.cpp b/lib/MC/ConstantPools.cpp
index 8c94e27..ca54402 100644 (file)
--- a/lib/MC/ConstantPools.cpp
+++ b/lib/MC/ConstantPools.cpp
@@ -57,6 +57,10 @@ const MCExpr *ConstantPool::addEntry(const MCExpr *Value, MCContext &Context,
 
 bool ConstantPool::empty() { return Entries.empty(); }
 
+void ConstantPool::clearCache() {
+  CachedEntries.clear();
+}
+
 //
 // AssemblerConstantPools implementation
 //
@@ -98,6 +102,13 @@ void AssemblerConstantPools::emitForCurrentSection(MCStreamer &Streamer) {
   }
 }
 
+void AssemblerConstantPools::clearCacheForCurrentSection(MCStreamer &Streamer) {
+  MCSection *Section = Streamer.getCurrentSectionOnly();
+  if (ConstantPool *CP = getConstantPool(Section)) {
+    CP->clearCache();
+  }
+}
+
 const MCExpr *AssemblerConstantPools::addEntry(MCStreamer &Streamer,
                                                const MCExpr *Expr,
                                                unsigned Size, SMLoc Loc) {

diff --git a/lib/Target/ARM/MCTargetDesc/ARMTargetStreamer.cpp b/lib/Target/ARM/MCTargetDesc/ARMTargetStreamer.cpp
index 2b0cd46..4a94318 100644 (file)
--- a/lib/Target/ARM/MCTargetDesc/ARMTargetStreamer.cpp
+++ b/lib/Target/ARM/MCTargetDesc/ARMTargetStreamer.cpp
@@ -38,6 +38,7 @@ const MCExpr *ARMTargetStreamer::addConstantPoolEntry(const MCExpr *Expr, SMLoc
 
 void ARMTargetStreamer::emitCurrentConstantPool() {
   ConstantPools->emitForCurrentSection(Streamer);
+  ConstantPools->clearCacheForCurrentSection(Streamer);
 }
 
 // finish() - write out any non-empty assembler constant pools.

diff --git a/test/MC/ARM/ltorg-range.s b/test/MC/ARM/ltorg-range.s
new file mode 100644 (file)
index 0000000..5c27d4c
--- /dev/null
+++ b/test/MC/ARM/ltorg-range.s
@@ -0,0 +1,27 @@
+@ RUN: llvm-mc -triple armv7-unknown-linux-gnueabi -filetype obj -o - %s \
+@ RUN:   | llvm-objdump -d - | FileCheck %s
+
+        ldr r0, =0x01020304
+@ CHECK: ldr
+        .ltorg
+@ CHECK: 0x01020304
+        ldr r0, =0x01020304
+        ldr r0, =0x01020304
+        ldr r0, =0x01020304
+@ CHECK: ldr
+@ CHECK: ldr
+@ CHECK: ldr
+        .ltorg
+@ CHECK: 0x01020304
+    .rep 1028
+        .word 0
+    .endr
+@ CHECK: 0x00000000
+
+        ldr r0, =0x01020304
+@ CHECK: ldr
+        .ltorg
+@ CHECK: 0x01020304
+    .rep 1028
+        .word 0
+    .endr