Fix PR5694. The CMN instructions set the flags differently from CMP, so they

cannot be directly interchanged for comparisons against negated values.
Disable the CMN instructions for the time being.

llvm-svn: 94119

5 files changed, 31 insertions, 15 deletions

diff --git a/llvm/lib/Target/ARM/ARMInstrInfo.td b/llvm/lib/Target/ARM/ARMInstrInfo.td
index b1efab1e2fd..af508ee131a 100644
--- a/llvm/lib/Target/ARM/ARMInstrInfo.td
+++ b/llvm/lib/Target/ARM/ARMInstrInfo.td
@@ -1539,8 +1539,10 @@ def : ARMV6Pat<(or (and GPR:$src1, 0xFFFF0000),
 
 defm CMP  : AI1_cmp_irs<0b1010, "cmp",
                         BinOpFrag<(ARMcmp node:$LHS, node:$RHS)>>;
-defm CMN  : AI1_cmp_irs<0b1011, "cmn",
-                        BinOpFrag<(ARMcmp node:$LHS,(ineg node:$RHS))>>;
+//FIXME: Disable CMN, as CCodes are backwards from compare expectations
+//       Compare-to-zero still works out, just not the relationals
+//defm CMN  : AI1_cmp_irs<0b1011, "cmn",
+//                        BinOpFrag<(ARMcmp node:$LHS,(ineg node:$RHS))>>;
 
 // Note that TST/TEQ don't set all the same flags that CMP does!
 defm TST  : AI1_cmp_irs<0b1000, "tst",
@@ -1553,11 +1555,11 @@ defm CMPz  : AI1_cmp_irs<0b1010, "cmp",
 defm CMNz  : AI1_cmp_irs<0b1011, "cmn",
                          BinOpFrag<(ARMcmpZ node:$LHS,(ineg node:$RHS))>>;
 
-def : ARMPat<(ARMcmp GPR:$src, so_imm_neg:$imm),
-             (CMNri  GPR:$src, so_imm_neg:$imm)>;
+//def : ARMPat<(ARMcmp GPR:$src, so_imm_neg:$imm),
+//             (CMNri  GPR:$src, so_imm_neg:$imm)>;
 
 def : ARMPat<(ARMcmpZ GPR:$src, so_imm_neg:$imm),
-             (CMNri  GPR:$src, so_imm_neg:$imm)>;
+             (CMNzri  GPR:$src, so_imm_neg:$imm)>;
 
 
 // Conditional moves
diff --git a/llvm/lib/Target/ARM/ARMInstrThumb.td b/llvm/lib/Target/ARM/ARMInstrThumb.td
index c304ff9caa7..746caffe22e 100644
--- a/llvm/lib/Target/ARM/ARMInstrThumb.td
+++ b/llvm/lib/Target/ARM/ARMInstrThumb.td
@@ -534,10 +534,12 @@ def tBIC : T1sIt<(outs tGPR:$dst), (ins tGPR:$lhs, tGPR:$rhs), IIC_iALUr,
 
 // CMN register
 let Defs = [CPSR] in {
-def tCMN : T1pI<(outs), (ins tGPR:$lhs, tGPR:$rhs), IIC_iCMPr,
-                "cmn", "\t$lhs, $rhs",
-                [(ARMcmp tGPR:$lhs, (ineg tGPR:$rhs))]>,
-           T1DataProcessing<0b1011>;
+//FIXME: Disable CMN, as CCodes are backwards from compare expectations
+//       Compare-to-zero still works out, just not the relationals
+//def tCMN : T1pI<(outs), (ins tGPR:$lhs, tGPR:$rhs), IIC_iCMPr,
+//                "cmn", "\t$lhs, $rhs",
+//                [(ARMcmp tGPR:$lhs, (ineg tGPR:$rhs))]>,
+//           T1DataProcessing<0b1011>;
 def tCMNz : T1pI<(outs), (ins tGPR:$lhs, tGPR:$rhs), IIC_iCMPr,
                  "cmn", "\t$lhs, $rhs",
                  [(ARMcmpZ tGPR:$lhs, (ineg tGPR:$rhs))]>,
diff --git a/llvm/lib/Target/ARM/ARMInstrThumb2.td b/llvm/lib/Target/ARM/ARMInstrThumb2.td
index 34a793cbbd2..c7591d21cd1 100644
--- a/llvm/lib/Target/ARM/ARMInstrThumb2.td
+++ b/llvm/lib/Target/ARM/ARMInstrThumb2.td
@@ -1609,16 +1609,18 @@ defm t2CMP  : T2I_cmp_irs<0b1101, "cmp",
 defm t2CMPz : T2I_cmp_irs<0b1101, "cmp",
                           BinOpFrag<(ARMcmpZ node:$LHS, node:$RHS)>>;
 
-defm t2CMN  : T2I_cmp_irs<0b1000, "cmn",
-                          BinOpFrag<(ARMcmp node:$LHS,(ineg node:$RHS))>>;
+//FIXME: Disable CMN, as CCodes are backwards from compare expectations
+//       Compare-to-zero still works out, just not the relationals
+//defm t2CMN  : T2I_cmp_irs<0b1000, "cmn",
+//                          BinOpFrag<(ARMcmp node:$LHS,(ineg node:$RHS))>>;
 defm t2CMNz : T2I_cmp_irs<0b1000, "cmn",
                           BinOpFrag<(ARMcmpZ node:$LHS,(ineg node:$RHS))>>;
 
-def : T2Pat<(ARMcmp  GPR:$src, t2_so_imm_neg:$imm),
-            (t2CMNri GPR:$src, t2_so_imm_neg:$imm)>;
+//def : T2Pat<(ARMcmp  GPR:$src, t2_so_imm_neg:$imm),
+//            (t2CMNri GPR:$src, t2_so_imm_neg:$imm)>;
 
 def : T2Pat<(ARMcmpZ  GPR:$src, t2_so_imm_neg:$imm),
-            (t2CMNri   GPR:$src, t2_so_imm_neg:$imm)>;
+            (t2CMNzri GPR:$src, t2_so_imm_neg:$imm)>;
 
 defm t2TST  : T2I_cmp_irs<0b0000, "tst",
                           BinOpFrag<(ARMcmpZ (and node:$LHS, node:$RHS), 0)>>;
diff --git a/llvm/lib/Target/ARM/README.txt b/llvm/lib/Target/ARM/README.txt
index 11c48add21b..a6f26a5dfe1 100644
--- a/llvm/lib/Target/ARM/README.txt
+++ b/llvm/lib/Target/ARM/README.txt
@@ -596,3 +596,12 @@ Make use of the "rbit" instruction.
 
 Take a look at test/CodeGen/Thumb2/machine-licm.ll. ARM should be taught how
 to licm and cse the unnecessary load from cp#1.
+
+//===---------------------------------------------------------------------===//
+
+The CMN instruction sets the flags like an ADD instruction, while CMP sets
+them like a subtract. Therefore to be able to use CMN for comparisons other
+than the Z bit, we'll need additional logic to reverse the conditionals
+associated with the comparison. Perhaps a pseudo-instruction for the comparison,
+with a post-codegen pass to clean up and handle the condition codes?
+See PR5694 for testcase.
diff --git a/llvm/lib/Target/ARM/Thumb2SizeReduction.cpp b/llvm/lib/Target/ARM/Thumb2SizeReduction.cpp
index 35359aa549a..95288bfc261 100644
--- a/llvm/lib/Target/ARM/Thumb2SizeReduction.cpp
+++ b/llvm/lib/Target/ARM/Thumb2SizeReduction.cpp
@@ -65,7 +65,8 @@ namespace {
     { ARM::t2ASRri, ARM::tASRri,  0,             5,   0,    1,   0,  0,0, 0 },
     { ARM::t2ASRrr, 0,            ARM::tASRrr,   0,   0,    0,   1,  0,0, 0 },
     { ARM::t2BICrr, 0,            ARM::tBIC,     0,   0,    0,   1,  0,0, 0 },
-    { ARM::t2CMNrr, ARM::tCMN,    0,             0,   0,    1,   0,  2,0, 0 },
+    //FIXME: Disable CMN, as CCodes are backwards from compare expectations
+    //{ ARM::t2CMNrr, ARM::tCMN,    0,             0,   0,    1,   0,  2,0, 0 },
     { ARM::t2CMPri, ARM::tCMPi8,  0,             8,   0,    1,   0,  2,0, 0 },
     { ARM::t2CMPrr, ARM::tCMPhir, 0,             0,   0,    0,   0,  2,0, 0 },
     { ARM::t2CMPzri,ARM::tCMPzi8, 0,             8,   0,    1,   0,  2,0, 0 },