AMDGPU: Undo sub x, c -> add x, -c canonicalization

This is worse if the original constant is an inline immediate.

This should also be done for 64-bit adds, but requires fixing
operand folding bugs first.

llvm-svn: 293540

3 files changed, 30 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.td b/llvm/lib/Target/AMDGPU/SIInstrInfo.td
index cfa17739829..6f4746b7559 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.td
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.td
@@ -295,6 +295,19 @@ class VGPRImm <dag frag> : PatLeaf<frag, [{
   return Limit < 10;
 }]>;
 
+def NegateImm : SDNodeXForm<imm, [{
+  return CurDAG->getConstant(-N->getSExtValue(), SDLoc(N), MVT::i32);
+}]>;
+
+// TODO: When FP inline imm values work?
+def NegSubInlineConst32 : ImmLeaf<i32, [{
+  return Imm < -16 && Imm >= -64;
+}], NegateImm>;
+
+def NegSubInlineConst16 : ImmLeaf<i16, [{
+  return Imm < -16 && Imm >= -64;
+}], NegateImm>;
+
 //===----------------------------------------------------------------------===//
 // Custom Operands
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Target/AMDGPU/SIInstructions.td b/llvm/lib/Target/AMDGPU/SIInstructions.td
index 813abc915d9..06516b24f32 100644
--- a/llvm/lib/Target/AMDGPU/SIInstructions.td
+++ b/llvm/lib/Target/AMDGPU/SIInstructions.td
@@ -1125,6 +1125,15 @@ def : SHA256MaPattern <V_BFI_B32, V_XOR_B32_e64>;
 def : IntMed3Pat<V_MED3_I32, smax, smax_oneuse, smin_oneuse>;
 def : IntMed3Pat<V_MED3_U32, umax, umax_oneuse, umin_oneuse>;
 
+
+// Undo sub x, c -> add x, -c canonicalization since c is more likely
+// an inline immediate than -c.
+// TODO: Also do for 64-bit.
+def : Pat<
+  (add i32:$src0, (i32 NegSubInlineConst32:$src1)),
+  (S_SUB_I32 $src0, NegSubInlineConst32:$src1)
+>;
+
 //============================================================================//
 // Assembler aliases
 //============================================================================//
diff --git a/llvm/lib/Target/AMDGPU/VOP2Instructions.td b/llvm/lib/Target/AMDGPU/VOP2Instructions.td
index 78b4e2ec49a..cd5f044ecd5 100644
--- a/llvm/lib/Target/AMDGPU/VOP2Instructions.td
+++ b/llvm/lib/Target/AMDGPU/VOP2Instructions.td
@@ -494,6 +494,14 @@ def : Pat <
   (V_CNDMASK_B32_e64 (i32 0), (i32 -1), $src)
 >;
 
+// Undo sub x, c -> add x, -c canonicalization since c is more likely
+// an inline immediate than -c.
+// TODO: Also do for 64-bit.
+def : Pat<
+  (add i16:$src0, (i16 NegSubInlineConst16:$src1)),
+  (V_SUB_U16_e64 $src0, NegSubInlineConst16:$src1)
+>;
+
 } // End Predicates = [isVI]
 
 //===----------------------------------------------------------------------===//