Allow X86::COND_NE_OR_P and X86::COND_NP_OR_E to be reversed.

Currently, AnalyzeBranch() fails non-equality comparison between floating points
on X86 (see https://llvm.org/bugs/show_bug.cgi?id=23875). This is because this
function can modify the branch by reversing the conditional jump and removing
unconditional jump if there is a proper fall-through. However, in the case of
non-equality comparison between floating points, this can turn the branch
"unanalyzable". Consider the following case:

jne.BB1
jp.BB1
jmp.BB2
.BB1:
...
.BB2:
...

AnalyzeBranch() will reverse "jp .BB1" to "jnp .BB2" and then "jmp .BB2" will be
removed:

jne.BB1
jnp.BB2
.BB1:
...
.BB2:
...

However, AnalyzeBranch() cannot analyze this branch anymore as there are two
conditional jumps with different targets. This may disable some optimizations
like block-placement: in this case the fall-through behavior is enforced even if
the fall-through block is very cold, which is suboptimal.

Actually this optimization is also done in block-placement pass, which means we
can remove this optimization from AnalyzeBranch(). However, currently
X86::COND_NE_OR_P and X86::COND_NP_OR_E are not reversible: there is no defined
negation conditions for them.

In order to reverse them, this patch defines two new CondCode X86::COND_E_AND_NP
and X86::COND_P_AND_NE. It also defines how to synthesize instructions for them.
Here only the second conditional jump is reversed. This is valid as we only need
them to do this "unconditional jump removal" optimization.


Differential Revision: http://reviews.llvm.org/D11393

llvm-svn: 264199

1 files changed, 48 insertions, 48 deletions

diff --git a/llvm/lib/Target/X86/X86InstrInfo.h b/llvm/lib/Target/X86/X86InstrInfo.h
index 3e3f2af7641..7439fa2f740 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.h
+++ b/llvm/lib/Target/X86/X86InstrInfo.h
@@ -29,54 +29,54 @@ namespace llvm {
 namespace X86 {
   // X86 specific condition code. These correspond to X86_*_COND in
   // X86InstrInfo.td. They must be kept in synch.
-  enum CondCode {
-    COND_A  = 0,
-    COND_AE = 1,
-    COND_B  = 2,
-    COND_BE = 3,
-    COND_E  = 4,
-    COND_G  = 5,
-    COND_GE = 6,
-    COND_L  = 7,
-    COND_LE = 8,
-    COND_NE = 9,
-    COND_NO = 10,
-    COND_NP = 11,
-    COND_NS = 12,
-    COND_O  = 13,
-    COND_P  = 14,
-    COND_S  = 15,
-    LAST_VALID_COND = COND_S,
-
-    // Artificial condition codes. These are used by AnalyzeBranch
-    // to indicate a block terminated with two conditional branches to
-    // the same location. This occurs in code using FCMP_OEQ or FCMP_UNE,
-    // which can't be represented on x86 with a single condition. These
-    // are never used in MachineInstrs.
-    COND_NE_OR_P,
-    COND_NP_OR_E,
-
-    COND_INVALID
-  };
-
-  // Turn condition code into conditional branch opcode.
-  unsigned GetCondBranchFromCond(CondCode CC);
-
-  /// \brief Return a set opcode for the given condition and whether it has
-  /// a memory operand.
-  unsigned getSETFromCond(CondCode CC, bool HasMemoryOperand = false);
-
-  /// \brief Return a cmov opcode for the given condition, register size in
-  /// bytes, and operand type.
-  unsigned getCMovFromCond(CondCode CC, unsigned RegBytes,
-                           bool HasMemoryOperand = false);
-
-  // Turn CMov opcode into condition code.
-  CondCode getCondFromCMovOpc(unsigned Opc);
-
-  /// GetOppositeBranchCondition - Return the inverse of the specified cond,
-  /// e.g. turning COND_E to COND_NE.
-  CondCode GetOppositeBranchCondition(CondCode CC);
+enum CondCode {
+  COND_A = 0,
+  COND_AE = 1,
+  COND_B = 2,
+  COND_BE = 3,
+  COND_E = 4,
+  COND_G = 5,
+  COND_GE = 6,
+  COND_L = 7,
+  COND_LE = 8,
+  COND_NE = 9,
+  COND_NO = 10,
+  COND_NP = 11,
+  COND_NS = 12,
+  COND_O = 13,
+  COND_P = 14,
+  COND_S = 15,
+  LAST_VALID_COND = COND_S,
+
+  // Artificial condition codes. These are used by AnalyzeBranch
+  // to indicate a block terminated with two conditional branches that together
+  // form a compound condition. They occur in code using FCMP_OEQ or FCMP_UNE,
+  // which can't be represented on x86 with a single condition. These
+  // are never used in MachineInstrs and are inverses of one another.
+  COND_NE_OR_P,
+  COND_E_AND_NP,
+
+  COND_INVALID
+};
+
+// Turn condition code into conditional branch opcode.
+unsigned GetCondBranchFromCond(CondCode CC);
+
+/// \brief Return a set opcode for the given condition and whether it has
+/// a memory operand.
+unsigned getSETFromCond(CondCode CC, bool HasMemoryOperand = false);
+
+/// \brief Return a cmov opcode for the given condition, register size in
+/// bytes, and operand type.
+unsigned getCMovFromCond(CondCode CC, unsigned RegBytes,
+                         bool HasMemoryOperand = false);
+
+// Turn CMov opcode into condition code.
+CondCode getCondFromCMovOpc(unsigned Opc);
+
+/// GetOppositeBranchCondition - Return the inverse of the specified cond,
+/// e.g. turning COND_E to COND_NE.
+CondCode GetOppositeBranchCondition(CondCode CC);
 }  // end namespace X86;