[PATCH, PR 49516] Avoid SRA mem-refing its scalar replacements

Martin Jambor mjambor@suse.cz
Thu Jun 23 20:41:00 GMT 2011


Hi,

When SRA tries to modify an assignment where on one side it should put
a new scalar replacement but the other is actually an aggregate with
a number of replacements for it, it will generate MEM-REFs into the
former replacement which can lead to miscompilations.

This is avoided by the simple patch below.  With it, we deal with
these situations like with other type-casts that SRA cannot handle: we
channel the data through the original variable and the original
statement.

The testcase is not miscompiled with 4.6 gcc but the bug is just
latent there.

I have verified the problem goes away on i686-linux.  I have
bootstrapped and tested the patch on x86_64-linux too.  I intend to do
a full i686 bootstrap and test but so far have not managed to do it.

OK for trunk and 4.6 after it is unfrozen?

Thanks,

Martin


2011-06-22  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimizations/49516
	* tree-sra.c (sra_modify_assign): Choose the safe path for
	aggregate copies if we also did scalar replacements.

	* testsuite/g++.dg/tree-ssa/pr49516.C: New test.

Index: src/gcc/tree-sra.c
===================================================================
--- src.orig/gcc/tree-sra.c
+++ src/gcc/tree-sra.c
@@ -2804,7 +2804,8 @@ sra_modify_assign (gimple *stmt, gimple_
      there to do the copying and then load the scalar replacements of the LHS.
      This is what the first branch does.  */
 
-  if (gimple_has_volatile_ops (*stmt)
+  if (modify_this_stmt
+      || gimple_has_volatile_ops (*stmt)
       || contains_vce_or_bfcref_p (rhs)
       || contains_vce_or_bfcref_p (lhs))
     {
Index: src/gcc/testsuite/g++.dg/tree-ssa/pr49516.C
===================================================================
--- /dev/null
+++ src/gcc/testsuite/g++.dg/tree-ssa/pr49516.C
@@ -0,0 +1,86 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+extern "C" void abort (void);
+
+typedef int int32;
+typedef unsigned int uint32;
+typedef unsigned long long uint64;
+typedef short int16;
+
+class Tp {
+ public:
+  Tp(int, const int segment, const int index) __attribute__((noinline));
+
+  inline bool operator==(const Tp& other) const;
+  inline bool operator!=(const Tp& other) const;
+  int GetType() const { return type_; }
+  int GetSegment() const { return segment_; }
+  int GetIndex() const { return index_; }
+ private:
+  inline static bool IsValidSegment(const int segment);
+  static const int kSegmentBits = 28;
+  static const int kTypeBits = 4;
+  static const int kMaxSegment = (1 << kSegmentBits) - 1;
+
+  union {
+
+    struct {
+      int32 index_;
+      uint32 segment_ : kSegmentBits;
+      uint32 type_ : kTypeBits;
+    };
+    struct {
+      int32 dummy_;
+      uint32 type_and_segment_;
+    };
+    uint64 value_;
+  };
+};
+
+Tp::Tp(int t, const int segment, const int index)
+ : index_(index), segment_(segment), type_(t) {}
+
+inline bool Tp::operator==(const Tp& other) const {
+  return value_ == other.value_;
+}
+inline bool Tp::operator!=(const Tp& other) const {
+  return value_ != other.value_;
+}
+
+class Range {
+ public:
+  inline Range(const Tp& position, const int count) __attribute__((always_inline));
+  inline Tp GetBeginTokenPosition() const;
+  inline Tp GetEndTokenPosition() const;
+ private:
+  Tp position_;
+  int count_;
+  int16 begin_index_;
+  int16 end_index_;
+};
+
+inline Range::Range(const Tp& position,
+                    const int count)
+    : position_(position), count_(count), begin_index_(0), end_index_(0)
+    { }
+
+inline Tp Range::GetBeginTokenPosition() const {
+  return position_;
+}
+inline Tp Range::GetEndTokenPosition() const {
+  return Tp(position_.GetType(), position_.GetSegment(),
+            position_.GetIndex() + count_);
+}
+
+int main ()
+{
+  Range range(Tp(0, 0, 3), 0);
+  if (!(range.GetBeginTokenPosition() == Tp(0, 0, 3)))
+    abort ();
+
+  if (!(range.GetEndTokenPosition() == Tp(0, 0, 3)))
+    abort();
+
+  return 0;
+}



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